{"id":1101,"date":"2016-11-04T03:36:16","date_gmt":"2016-11-04T03:36:16","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/microbiology\/?post_type=chapter&#038;p=1101"},"modified":"2018-07-12T11:34:02","modified_gmt":"2018-07-12T11:34:02","slug":"parasitic-infections-of-the-circulatory-and-lymphatic-systems","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/chapter\/parasitic-infections-of-the-circulatory-and-lymphatic-systems\/","title":{"raw":"Parasitic Infections of the Circulatory and Lymphatic Systems","rendered":"Parasitic Infections of the Circulatory and Lymphatic Systems"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Objectives<\/h3>\r\n<ul>\r\n \t<li>Identify common parasites that cause infections of the circulatory and lymphatic systems<\/li>\r\n \t<li>Compare the major characteristics of specific parasitic diseases affecting the circulatory and lymphatic systems<\/li>\r\n<\/ul>\r\n<\/div>\r\nSome protozoa and parasitic flukes are also capable of causing infections of the human circulatory system. Although these infections are rare in the US, they continue to cause widespread suffering in the developing world today. Fungal infections of the circulatory system are very rare. Therefore, they are not discussed in this chapter.\r\n<h2>Malaria<\/h2>\r\nDespite more than a century of intense research and clinical advancements, <strong>malaria<\/strong> remains one of the most important infectious diseases in the world today. Its widespread distribution places more than half of the world\u2019s population in jeopardy. In 2015, the WHO estimated there were about 214 million cases of malaria worldwide, resulting in about 438,000 deaths; about 88% of cases and 91% of deaths occurred in Africa.[footnote]World Health Organization. \"World Malaria Report 2015: Summary.\" 2015. http:\/\/www.who.int\/malaria\/publications\/world-malaria-report-2015\/report\/en\/. Accessed July 28, 2016.[\/footnote] Although malaria is not currently a major threat in the US, the possibility of its reintroduction is a concern. Malaria is caused by several protozoan parasites in the genus <strong><em>Plasmodium<\/em><\/strong>: <em>P. falciparum, P. knowlesi, P. malariae, P. ovale,<\/em> and <em>P. vivax. Plasmodium<\/em> primarily infect red blood cells and are transmitted through the bite of <strong><em>Anopheles<\/em> mosquitoes<\/strong>.\r\n\r\nCurrently, <em>P. falciparum<\/em> is the most common and most lethal cause of malaria, often called falciparum malaria. Falciparum malaria is widespread in highly populated regions of Africa and Asia, putting many people at risk for the most severe form of the disease.\r\n\r\nThe classic signs and symptoms of malaria are cycles of extreme fever and chills. The sudden, violent symptoms of malaria start with malaise, abrupt chills, and fever (39\u201341\u00b0 C [102.2\u2013105.8 \u00b0F]), rapid and faint pulse, polyuria, headache, myalgia, nausea, and vomiting. After 2 to 6 hours of these symptoms, the fever falls, and profuse sweating occurs for 2 to 3 hours, followed by extreme fatigue. These symptoms are a result of <em>Plasmodium<\/em> emerging from red blood cells synchronously, leading to simultaneous rupture of a large number of red blood cells, resulting in damage to the spleen, liver, lymph nodes, and bone marrow. The organ damage resulting from hemolysis causes patients to develop sludge blood (i.e., blood in which the red blood cells agglutinate into clumps) that can lead to lack of oxygen, necrosis of blood vessels, organ failure, and death.\r\n\r\nIn established infections, malarial cycles of fever and chills typically occur every 2 days in the disease described as <strong>tertian malaria<\/strong>, which is caused by <em>P. vivax<\/em> and <em>P. ovale<\/em>. The cycles occur every 3 days in the disease described as <strong>quartan malaria<\/strong>, which is caused by <em>P. malariae<\/em>. These intervals may vary among cases.\r\n\r\n<em>Plasmodium<\/em> has a complex life cycle that includes several developmental stages alternately produced in mosquitoes and humans (Figure\u00a01). When an infected mosquito takes a blood meal, sporozoites in the mosquito salivary gland are injected into the host\u2019s blood. These parasites circulate to the liver, where they develop into schizonts. The schizonts then undergo <strong>schizogony<\/strong>, resulting in the release of many merozoites at once. The merozoites move to the bloodstream and infect red blood cells. Inside red blood cells, merozoites develop into trophozoites that produce more merozoites. The synchronous release of merozoites from red blood cells in the evening leads to the symptoms of malaria.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"1300\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03175823\/OSC_Microbio_25_04_Malaria.jpg\" alt=\"Life cycle of Plasmodium. [Human Liver Stages] 1 \u2013 Mosquito take a blood meal and injects Plasmodium into a human. 2 \u2013 Plasmodium infects liver cell. 3 \u2013 Plasmodium multiplies in liver cell. [Human Blood Stages] 4 \u2013 Plasmodium enters blood. An immature ring stage looks like a signet ring in a red blood cell. This becomes a mature ring stage and undergoes mitosis to produce schizonts which are released by rupturing the red blood cells. 5 \u2013 Gametes (1n) produced by meiosis. [Mosquito Stages] 6 - Moquito takes a blood meal and ingests gametes. 7 \u2013 Microgametes fertilizes macrogamete. 8 \u2013 Zygote (2n) forms. 9 \u2013 Zygote undergoes mitosis. 10 \u2013 Parasite differentiates and enters the saliva of the mosquito.\" width=\"1300\" height=\"872\" \/> Figure\u00a01. The life cycle of <em>Plasmodium<\/em>. (credit: modification of work by Centers for Disease Control and Prevention)[\/caption]\r\n\r\n[caption id=\"\" align=\"alignright\" width=\"399\"]<img class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03175827\/OSC_Microbio_25_04_BloodSmear.jpg\" alt=\"A micrograph showing red blood cells. A dark ring in the center of one cell is labeled ring form. A larger dark region in another cell is labeled schizont.\" width=\"399\" height=\"254\" \/> Figure\u00a02. A blood smear (human blood stage) shows an early trophozoite in a delicate ring form (upper left) and an early stage schizont form (center) of Plasmodium falciparum from a patient with malaria. (credit: modification of work by Centers for Disease Control and Prevention)[\/caption]\r\n\r\nIn addition, some trophozoites alternatively develop into male and female gametocytes. The gametocytes are taken up when the mosquito takes a blood meal from an infected individual. Sexual sporogony occurs in the gut of the mosquito. The gametocytes fuse to form zygotes in the insect gut. The zygotes become motile and elongate into an ookinete. This form penetrates the midgut wall and develops into an oocyst. Finally, the oocyst releases new sporozoites that migrate to the mosquito salivary glands to complete the life cycle.\r\n\r\nDiagnosis of malaria is by microscopic observation of developmental forms of <em>Plasmodium<\/em> in blood smears and rapid EIA assays that detect <em>Plasmodium<\/em> antigens or enzymes (Figure\u00a02). Drugs such as <strong>chloroquine<\/strong>, <strong>atovaquone<\/strong> , <strong>artemether<\/strong>, and <strong>lumefantrine<\/strong> may be prescribed for both acute and prophylactic therapy, although some <em>Plasmodium<\/em> spp. have shown resistance to antimalarial drugs. Use of insecticides and insecticide-treated bed nets can limit the spread of malaria. Despite efforts to develop a vaccine for malaria, none is currently available.\r\n<div class=\"textbox\">Visit this site to <a href=\"https:\/\/www.animalplanet.com\/tv-shows\/monsters-inside-me\/videos\/malaria-parasite\/\" target=\"_blank\" rel=\"noopener\">learn how the parasite <em>Plasmodium<\/em> infects red blood cells<\/a>.<\/div>\r\n<div class=\"textbox\">The <a href=\"http:\/\/nothingbutnets.net\/\" target=\"_blank\" rel=\"noopener\">Nothing But Nets campaign<\/a>, an initiative of the United Nations Foundation, has partnered with the Bill and Melinda Gates Foundation to make mosquito bed nets available in developing countries in Africa.<\/div>\r\n<h2>Toxoplasmosis<\/h2>\r\nThe disease <strong>toxoplasmosis<\/strong> is caused by the protozoan <strong><em>Toxoplasma gondii<\/em><\/strong>. <em>T. gondii<\/em> is found in a wide variety of birds and mammals,[footnote]A.M. Tenter et al.. \"<em>Toxoplasma gondii<\/em>: From Animals to Humans.\" <em>International Journal for Parasitology<\/em> 30 no. 12-13 (2000):1217\u20131258.[\/footnote] and human infections are common. The Centers for Disease Control and Prevention (CDC) estimates that 22.5% of the population 12 years and older has been infected with <em>T. gondii<\/em>; but immunocompetent individuals are typically asymptomatic, however.[footnote]Centers for Disease Control and Prevention. \"Parasites - Toxoplasmosis (Toxoplasma Infection). Epidemiology &amp; Risk Factors.\" 2015 http:\/\/www.cdc.gov\/parasites\/toxoplasmosis\/epi.html. Accessed July 28, 2016.[\/footnote] Domestic cats are the only known definitive hosts for the sexual stages of <em>T. gondii<\/em> and, thus, are the main reservoirs of infection. Infected cats shed <em>T. gondii<\/em> oocysts in their feces, and these oocysts typically spread to humans through contact with fecal matter on cats\u2019 bodies, in litter boxes, or in garden beds where outdoor cats defecate.\r\n\r\n<em>T. gondii<\/em> has a complex <strong>life cycle<\/strong> that involves multiple hosts. The <em>T. gondii<\/em> life cycle begins when unsporulated oocysts are shed in the cat\u2019s feces. These oocysts take 1\u20135 days to sporulate in the environment and become infective. Intermediate hosts in nature include birds and rodents, which become infected after ingesting soil, water, or plant material contaminated with the infective oocysts. Once ingested<em>,<\/em> the oocysts transform into tachyzoites that localize in the bird or rodent neural and muscle tissue, where they develop into tissue cysts. Cats may become infected after consuming birds and rodents harboring tissue cysts. Cats and other animals may also become infected directly by ingestion of sporulated oocysts in the environment. Interestingly, <em>Toxoplasma<\/em> infection appears to be able to modify the host\u2019s behavior. Mice infected by <em>Toxoplasma<\/em> lose their fear of cat pheromones. As a result, they become easier prey for cats, facilitating the transmission of the parasite to the cat definitive host[footnote]J. Flegr. \"Effects of <em>Toxoplasma<\/em> on Human Behavior.\" <em>Schizophrenia Bulletin<\/em> 33, no. 3 (2007):757\u2013760.[\/footnote] (Figure\u00a03).\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"1300\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03175833\/OSC_Microbio_25_04_Toxoplasma.jpg\" alt=\"Life cycle of Toxoplasma gondii. 1 - Insporulated oocysts are shed in the cat\u2019s feces. 2 \u2013 Intermediate host in nature (including birds and rodents) become infected after ingesting soil, water or plant material contaminated with oocysts. 3 \u2013 Oocysts transform into tachyzoites shortly after ingestion. These tachyzoites localize in neural and muscle tissue and develop into tissue cyst bradyzoites. 4 - Cats eat infected animals (such as rodents or birsds) and shed unsporulated oocysts. 5 \u2013 Intermediate hosts (such as pigs and cows) ingeset oocysts from contaminated water, soil, or plant material. 6 \u2013 Humans can become infected when they eat undercooked meat of infected animals harboring tissue cysts. 7 \u2013 Humans can also become infected when they consume food or water contaminate with cat feces or by handling fecal-contaminated soil or cat\u2019s litter box. 8 \u2013 Humans can also become infected via the placenta from fetus to mother. 10 \u2013 Tissue cysts can form in skeletal muscle, myocardium, brain, and eyes. 11 \u2013 Diagnosis of congenital infection can be achieved by detecting T. gondii DNA in amniotic fluid using molecular methods such as PCR.\" width=\"1300\" height=\"1310\" \/> Figure\u00a03. The infectious cycle of <em>Toxoplasma gondii<\/em>. (credit: \"diagram\": modification of work by Centers for Disease Control and Prevention; credit \"cat\": modification of work by \"KaCey97078\"\/Flickr)[\/caption]\r\n\r\n<em>Toxoplasma<\/em> infections in humans are extremely common, but most infected people are asymptomatic or have subclinical symptoms. Some studies suggest that the parasite may be able to influence the personality and psychomotor performance of infected humans, similar to the way it modifies behavior in other mammals.[footnote]Ibid.[\/footnote] When symptoms do occur, they tend to be mild and similar to those of mononucleosis. However, asymptomatic toxoplasmosis can become problematic in certain situations. Cysts can lodge in a variety of human tissues and lie dormant for years. Reactivation of these quiescent infections can occur in immunocompromised patients following transplantation, cancer therapy, or the development of an immune disorder such as <strong>AIDS<\/strong>. In patients with AIDS who have toxoplasmosis, the immune system cannot combat the growth of <em>T. gondii<\/em> in body tissues; as a result, these cysts can cause encephalitis, retinitis, pneumonitis, cognitive disorders, and seizures that can eventually be fatal.\r\n\r\nToxoplasmosis can also pose a risk during <strong>pregnancy<\/strong> because tachyzoites can cross the placenta and cause serious infections in the developing fetus. The extent of fetal damage resulting from toxoplasmosis depends on the severity of maternal disease, the damage to the placenta, the gestational age of the fetus when infected, and the virulence of the organism. Congenital toxoplasmosis often leads to fetal loss or premature birth and can result in damage to the central nervous system, manifesting as mental retardation, deafness, or blindness. Consequently, pregnant women are advised by the CDC to take particular care in preparing meat, gardening, and caring for pet cats.[footnote]Centers for Disease Control and Prevention. \"Parasites - Toxoplasmosis (Toxoplasma infection). Toxoplasmosis Frequently Asked Questions (FAQs).\" 2013. http:\/\/www.cdc.gov\/parasites\/toxoplasmosis\/gen_info\/faqs.html. Accessed July 28, 2016.[\/footnote] Diagnosis of toxoplasmosis infection during pregnancy is usually achieved by serology including <strong>TORCH<\/strong> testing (the \"T\" in TORCH stands for toxoplasmosis). Diagnosis of congenital infections can also be achieved by detecting <em>T. gondii<\/em> DNA in amniotic fluid, using molecular methods such as PCR.\r\n\r\nIn adults, diagnosis of toxoplasmosis can include observation of tissue cysts in tissue specimens. Tissue cysts may be observed in Giemsa- or Wright-stained biopsy specimens, and CT, magnetic resonance imaging, and lumbar puncture can also be used to confirm infection (Figure\u00a04).\r\n\r\nPreventing infection is the best first-line defense against toxoplasmosis. Preventive measures include washing hands thoroughly after handling raw meat, soil, or cat litter, and avoiding consumption of vegetables possibly contaminated with cat feces. All meat should be cooked to an internal temperature of 73.9\u201376.7 \u00b0C (165\u2013170 \u00b0F).\r\n\r\nMost immunocompetent patients do not require clinical intervention for <em>Toxoplasma<\/em> infections. However, neonates, pregnant women, and immunocompromised patients can be treated with <strong>pyrimethamine<\/strong> and <strong>sulfadiazine<\/strong>\u2014except during the first trimester of pregnancy, because these drugs can cause birth defects. <strong>Spiramycin<\/strong> has been used safely to reduce transmission in pregnant women with primary infection during the first trimester because it does not cross the placenta.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"900\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03175836\/OSC_Microbio_25_04_SabinFeld.jpg\" alt=\"A) A micrograph of curved cells with a nucleus. B) micrograph of a sphere with many smaller spheres inside.\" width=\"900\" height=\"383\" \/> Figure\u00a04. (a) Giemsa-stained <em>Toxoplasma gondii<\/em> tachyzoites from a smear of peritoneal fluid obtained from a mouse inoculated with <em>T. gondii<\/em>. Tachyzoites are typically crescent shaped with a prominent, centrally placed nucleus. (b) Microscopic cyst containing <em>T. gondii<\/em> from mouse brain tissue. Thousands of resting parasites (stained red) are contained in a thin parasite cyst wall. (credit a: modification of work by Centers for Disease Control and Prevention; credit b: modification of work by USDA)[\/caption]\r\n<h2>Babesiosis<\/h2>\r\nBabesiosis is a rare zoonotic infectious disease caused by <strong><em>Babesia<\/em> spp<\/strong>. These parasitic protozoans infect various wild and domestic animals and can be transmitted to humans by black-legged <em>Ixodes<\/em> ticks. In humans, <em>Babesia<\/em> infect red blood cells and replicate inside the cell until it ruptures. The <em>Babesia<\/em> released from the ruptured red blood cell continue the growth cycle by invading other red blood cells. Patients may be asymptomatic, but those who do have symptoms often initially experience malaise, fatigue, chills, fever, headache, myalgia, and arthralgia. In rare cases, particularly in asplenic (absence of the spleen) patients, the elderly, and patients with <strong>AIDS<\/strong>, <strong>babesiosis<\/strong> may resemble falciparum malaria, with high fever, hemolytic anemia, hemoglobinuria (hemoglobin or blood in urine), jaundice, and renal failure, and the infection can be fatal. Previously acquired asymptomatic Babesia infection may become symptomatic if a splenectomy is performed.\r\n\r\n[caption id=\"\" align=\"alignright\" width=\"450\"]<img class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03175838\/OSC_Microbio_25_04_babesia.jpg\" alt=\"Micrograph of red blood cells with dark circles inside.\" width=\"450\" height=\"270\" \/> Figure\u00a05. In this blood smear from a patient with babesiosis, <em>Babesia<\/em> parasites can be observed in the red blood cells. (credit: modification of work by Centers for Disease Control and Prevention)[\/caption]\r\n\r\nDiagnosis is based mainly on the microscopic observation of parasites in blood smears (Figure\u00a05). Serologic and antibody detection by IFA can also be performed and PCR-based tests are available. Many people do not require clinical intervention for Babesia infections, however, serious infections can be cleared with a combination of <strong>atovaquone<\/strong> and <strong>azithromycin<\/strong> or a combination of <strong>clindamycin<\/strong> and <strong>quinine<\/strong>.\r\n<h2>Chagas Disease<\/h2>\r\nAlso called <strong>American trypanosomiasis<\/strong>, Chagas disease is a zoonosis classified as a <strong>neglected tropical disease<\/strong> (NTD). It is caused by the flagellated protozoan <strong><em>Trypanosoma cruzi<\/em><\/strong> and is most commonly transmitted to animals and people through the feces of triatomine bugs. The <strong>triatomine bug<\/strong> is nicknamed the kissing bug because it frequently bites humans on the face or around the eyes; the insect often defecates near the bite and the infected fecal matter may be rubbed into the bite wound by the bitten individual (Figure\u00a06). The bite itself is painless and, initially, many people show no signs of the disease. Alternative modes of transmission include contaminated blood transfusions, organ transplants from infected donors, and congenital transmission from mother to fetus.\r\n\r\nChagas disease is endemic throughout much of Mexico, Central America, and South America, where, according to WHO, an estimated 6 million to 7 million people are infected.[footnote]World Health Organization. \"Chagas disease (American trypanosomiasis). Fact Sheet.\" 2016. http:\/\/www.who.int\/mediacentre\/factsheets\/fs340\/en\/. Accessed July 29, 2016.[\/footnote] Currently, Chagas disease is not endemic in the US, even though triatomine bugs are found in the southern half of the country.\r\n\r\nTriatomine bugs typically are active at night, when they take blood meals by biting the faces and lips of people or animals as they sleep and often defecate near the site of the bite. Infection occurs when the host rubs the feces into their eyes, mouth, the bite wound, or another break in the skin. The protozoan then enters the blood and invades tissues of the heart and central nervous system, as well as macrophages and monocytes. Nonhuman reservoirs of <em>T. cruzi<\/em> parasites include wild animals and domesticated animals such as dogs and cats, which also act as reservoirs of the pathogen.[footnote]C.E. Reisenman et al. \"Infection of Kissing Bugs With <em>Trypanosoma cruzi<\/em>, Tucson, Arizona, USA.\" <em>Emerging Infectious Diseases<\/em> 16 no. 3 (2010):400\u2013405.[\/footnote]\r\n\r\nThere are three phases of Chagas disease: acute, intermediate, and chronic. These phases can be either asymptomatic or life-threatening depending on the immunocompetence status of the patient.\r\n\r\nIn acute phase disease, symptoms include fever, headache, myalgia, rash, vomiting, diarrhea, and enlarged spleen, liver, and lymph nodes. In addition, a localized nodule called a chagoma may form at the portal of entry, and swelling of the eyelids or the side of the face, called Roma\u00f1a's sign, may occur near the bite wound. Symptoms of the acute phase may resolve spontaneously, but if untreated, the infection can persist in tissues, causing irreversible damage to the heart or brain. In rare cases, young children may die of <strong>myocarditis<\/strong> or <strong>meningoencephalitis<\/strong> during the acute phase of Chagas disease.\r\n\r\nFollowing the acute phase is a prolonged intermediate phase during which few or no parasites are found in the blood and most people are asymptomatic. Many patients will remain asymptomatic for life; however, decades after exposure, an estimated 20%\u201330% of infected people will develop chronic disease that can be debilitating and sometimes life threatening. In the chronic phase, patients may develop painful swelling of the colon, leading to severe twisting, constipation, and bowel obstruction; painful swelling of the esophagus, leading to dysphagia and malnutrition; and <strong>flaccid cardiomegaly<\/strong> (enlargement of the heart), which can lead to heart failure and sudden death.\r\n\r\nDiagnosis can be confirmed through several different tests, including direct microscopic observation of trypanosomes in the blood, IFA, EIAs, PCR, and culturing in artificial media. In endemic regions, xenodiagnoses may be used; this method involves allowing uninfected kissing bugs to feed on the patient and then examining their feces for the presence of <em>T. cruzi<\/em>.\r\n\r\nThe medications <strong>nifurtimox<\/strong> and <strong>benznidazole<\/strong> are effective treatments during the acute phase of Chagas disease. The efficacy of these drugs is much lower when the disease is in the chronic phase. Avoiding exposure to the pathogen through vector control is the most effective method of limiting this disease.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"1200\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03175842\/OSC_Microbio_25_04_Trypanosom.jpg\" alt=\"a) Micrograph of red blood cells with crescent-shaped cells outside. These parasitic cells are about the length of 2 red blood cells. B) photo of a triatomine bug.\" width=\"1200\" height=\"547\" \/> Figure\u00a06. (a) <em>Trypanosoma cruzi<\/em> protozoan in a blood smear from a patient with Chagas disease. (b) The triatomine bug (also known as the kissing bug or assassin bug) is the vector of Chagas disease. (credit a: modification of work by Centers for Disease Control and Prevention; credit b: modification of work by Erwin Huebner)[\/caption]\r\n<h2>Leishmaniasis<\/h2>\r\nAlthough it is classified as an NTD, <strong>leishmaniasis<\/strong> is relatively widespread in tropical and subtropical regions, affecting people in more than 90 countries. It is caused by approximately 20 different species of <strong><em>Leishmania<\/em><\/strong>, protozoan parasites that are transmitted by <strong>sand fly<\/strong> vectors such as <em>Phlebotomus<\/em> spp. and <em>Lutzomyia<\/em> spp. Dogs, cats, sheep, horses, cattle rodents, and humans can all serve as reservoirs.\r\n\r\nThe <em>Leishmania<\/em> protozoan is phagocytosed by macrophages but uses virulence factors to avoid destruction within the phagolysosome. The virulence factors inhibit the phagolysosome enzymes that would otherwise destroy the parasite. The parasite reproduces within the macrophage, lyses it, and the progeny infect new macrophages (see <a href=\".\/chapter\/pathogen-recognition-and-phagocytosis\/\" target=\"_blank\" rel=\"noopener\">\"When Phagocytosis Fails\" in\u00a0Pathogen Recognition and Phagocytosis<\/a>).\r\n\r\nThe three major clinical forms of leishmaniasis are cutaneous (oriental sore, Delhi boil, Aleppo boil), visceral (kala-azar, Dumdum fever), and mucosal (espundia). The most common form of disease is <strong>cutaneous leishmaniasis<\/strong>, which is characterized by the formation of sores at the site of the insect bite that may start out as papules or nodules before becoming large ulcers (Figure\u00a07).\r\n\r\nIt may take <strong>visceral leishmaniasis<\/strong> months and sometimes years to develop, leading to enlargement of the lymph nodes, liver, spleen, and bone marrow. The damage to these body sites triggers fever, weight loss, and swelling of the spleen and liver. It also causes a decrease in the number of red blood cells (anemia), white blood cells (leukopenia), and platelets (thrombocytopenia), causing the patient to become immunocompromised and more susceptible to fatal infections of the lungs and gastrointestinal tract.\r\n\r\nThe mucosal form of leishmaniasis is one of the less common forms of the disease. It causes a lesion similar to the cutaneous form but <strong>mucosal leishmaniasis<\/strong> is associated with mucous membranes of the mouth, nares, or pharynx, and can be destructive and disfiguring. Mucosal leishmaniasis occurs less frequently when the original cutaneous (skin) infection is promptly treated.\r\n\r\nDefinitive diagnosis of leishmaniasis is made by visualizing organisms in Giemsa-stained smears, by isolating <em>Leishmania<\/em> protozoans in cultures, or by PCR-based assays of aspirates from infected tissues. Specific DNA probes or analysis of cultured parasites can help to distinguish <em>Leishmania<\/em> species that are causing simple cutaneous leishmaniasis from those capable of causing mucosal leishmaniasis.\r\n\r\nCutaneous leishmaniasis is usually not treated. The lesions will resolve after weeks (or several months), but may result in scarring. Recurrence rates are low for this disease. More serious infections can be treated with <strong>stibogluconate<\/strong> (antimony gluconate), <strong>amphotericin B<\/strong>, and <strong>miltefosine<\/strong>.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"1300\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03175846\/OSC_Microbio_25_04_Leishmania.jpg\" alt=\"a) Micrograph of a tissue sample. A black arrow points to leishmania mexicana. B) a large, open wound on skin.\" width=\"1300\" height=\"680\" \/> Figure\u00a07. (a) A micrograph of a tissue sample from a patient with localized cutaneous leishmaniasis. Parasitic <em>Leishmania mexicana<\/em> (black arrow) are visible in and around the host cells. (b) Large skin ulcers are associated with cutaneous leishmaniasis. (credit a: modification of work by Fern\u00e1ndez-Figueroa EA, Rangel-Escare\u00f1o C, Espinosa-Mateos V, Carrillo-S\u00e1nchez K, Salaiza-Suazo N, Carrada-Figueroa G, March-Mifsut S, and Becker I; credit b: modification of work by Jean Fortunet)[\/caption]\r\n<h2>Schistosomiasis<\/h2>\r\nSchistosomiasis (bilharzia) is an NTD caused by blood flukes in the genus <strong><em>Schistosoma<\/em><\/strong> that are native to the Caribbean, South America, Middle East, Asia, and Africa. Most human <strong>schistosomiasis<\/strong> cases are caused by <em>Schistosoma mansoni, S. haematobium<\/em>, or <em>S. japonicum<\/em>. <em>Schistosoma<\/em> are the only <strong>trematodes<\/strong> that invade through the skin; all other trematodes infect by ingestion. WHO estimates that at least 258 million people required preventive treatment for schistosomiasis in 2014.[footnote]World Health Organization. \"Schistosomiasis. Fact Sheet.\" 2016. http:\/\/www.who.int\/mediacentre\/factsheets\/fs115\/en\/. Accessed July 29, 2016.[\/footnote]\r\n\r\nInfected human hosts shed <em>Schistosoma<\/em> eggs in urine and feces, which can contaminate freshwater habitats of snails that serve as intermediate hosts. The eggs hatch in the water, releasing miracidia, an intermediate growth stage of the <em>Schistosoma<\/em> that infect the snails. The miracidia mature and multiply inside the snails, transforming into cercariae that leave the snail and enter the water, where they can penetrate the skin of swimmers and bathers. The cercariae migrate through human tissue and enter the bloodstream, where they mature into adult male and female worms that mate and release fertilized eggs. The eggs travel through the bloodstream and penetrate various body sites, including the bladder or intestine, from which they are excreted in urine or stool to start the life cycle over again (<a href=\".\/chapter\/parasitic-helminths\/\" target=\"_blank\" rel=\"noopener\">Figure\u00a04 in\u00a0Parasitic Helminths<\/a>).\r\n\r\nA few days after infection, patients may develop a rash or itchy skin associated with the site of cercariae penetration. Within 1\u20132 months of infection, symptoms may develop, including fever, chills, cough, and myalgia, as eggs that are not excreted circulate through the body. After years of infection, the eggs become lodged in tissues and trigger inflammation and scarring that can damage the liver, central nervous system, intestine, spleen, lungs, and bladder. This may cause abdominal pain, enlargement of the liver, blood in the urine or stool, and problems passing urine. Increased risk for bladder cancer is also associated with chronic <em>Schistosoma<\/em> infection. In addition, children who are repeatedly infected can develop malnutrition, anemia, and learning difficulties.\r\n\r\nDiagnosis of schistosomiasis is made by the microscopic observation of eggs in feces or urine, intestine or bladder tissue specimens, or serologic tests. The drug <strong>praziquantel<\/strong> is effective for the treatment of all schistosome infections. Improving wastewater management and educating at-risk populations to limit exposure to contaminated water can help control the spread of the disease.\r\n<h3>Cercarial Dermatitis<\/h3>\r\nThe cercaria of some species of <em>Schistosoma<\/em> can only transform into adult worms and complete their life cycle in animal hosts such as migratory birds and mammals. The cercaria of these worms are still capable of penetrating human skin, but they are unable to establish a productive infection in human tissue. Still, the presence of the cercaria in small blood vessels triggers an immune response, resulting in itchy raised bumps called <strong>cercarial dermatitis<\/strong> (also known as swimmer\u2019s itch or clam digger's itch). Although it is uncomfortable, cercarial dermatitis is typically self-limiting and rarely serious. Antihistamines and antipruritics can be used to limit inflammation and itching, respectively.\r\n<div class=\"textbox shaded\">\r\n<h3>Common Eukaryotic Pathogens of the Human Circulatory System<\/h3>\r\nProtozoan and helminthic infections are prevalent in the developing world. A few of the more important parasitic infections are summarized in Table 1.\r\n<table>\r\n<thead>\r\n<tr>\r\n<th colspan=\"6\">Table 1.\u00a0Parasitic Diseases of the Circulatory and Lymphatic Systems<\/th>\r\n<\/tr>\r\n<tr>\r\n<th>Disease<\/th>\r\n<th>Pathogen<\/th>\r\n<th>Signs and Symptoms<\/th>\r\n<th>Transmission<\/th>\r\n<th>Diagnostic Tests<\/th>\r\n<th>Antimicrobial Drugs<\/th>\r\n<\/tr>\r\n<\/thead>\r\n<tbody>\r\n<tr>\r\n<th colspan=\"6\">Protozoa<\/th>\r\n<\/tr>\r\n<tr>\r\n<td>Babesiosis<\/td>\r\n<td><em>Babesia<\/em> spp.<\/td>\r\n<td>Malaise, chills, fever, headache, myalgia, arthralgia<\/td>\r\n<td>From animals to humans via <em>Ixodes<\/em> tick vectors<\/td>\r\n<td>Blood smear, serology, IFA, and PCR<\/td>\r\n<td>Atovaquone and azithromycin or clindamycin and quinine<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Chagas disease<\/td>\r\n<td><em>Trypanosoma cruzi<\/em><\/td>\r\n<td>Fever, headache, body aches, swollen lymph nodes; potentially fatal<\/td>\r\n<td>Between humans or from animal reservoirs via triatomine (kissing bug) vector<\/td>\r\n<td>Blood smear, IFA, EIA, PCR, xenodiagnoses<\/td>\r\n<td>Nifurtimox, benznidazole<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Leishmaniasis<\/td>\r\n<td><em>Leishmania<\/em> spp.<\/td>\r\n<td>Ulcer; enlargement of the lymph nodes, liver, spleen, and other organs<\/td>\r\n<td>Between humans or from animal reservoirs via sand fly (<em>Phlebotomus<\/em>\u00a0spp., <em>Lutzomyia<\/em>\u00a0spp.) vectors<\/td>\r\n<td>Blood smear, culture, PCR, DNA probe, biopsy<\/td>\r\n<td>Stibogluconate, amphotericin\u00a0B, miltefosine<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Malaria<\/td>\r\n<td><em>Plasmodium vivax, P.\u00a0malariae, P.\u00a0falciparum, P.\u00a0ovale, P.\u00a0knowlesi<\/em><\/td>\r\n<td>Extreme fever, chills, myalgia, nausea, and vomiting, possibly leading to organ failure and death<\/td>\r\n<td>Between humans via Anopheles mosquito vectors<\/td>\r\n<td>Blood smear, EIA<\/td>\r\n<td>Chloroquine, atovaquone, artemether, and lumefantrine<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Toxoplasmosis<\/td>\r\n<td><em>Toxoplasma gondii<\/em><\/td>\r\n<td>Tissue cysts; in pregnant women, birth defects or miscarriage<\/td>\r\n<td>Contact with feces of infected cat; eating contaminated vegetables or undercooked meat of infected animal<\/td>\r\n<td>Serological tests, direct detection of pathogen in tissue sections<\/td>\r\n<td>Sulfadiazine, pyrimethamine, spiramycin<\/td>\r\n<\/tr>\r\n<tr>\r\n<th colspan=\"6\">Helminths<\/th>\r\n<\/tr>\r\n<tr>\r\n<td>Schistosomiasis<\/td>\r\n<td><em>Schistosoma<\/em> spp.<\/td>\r\n<td>Rash, fever, chills, myalgia; chronic inflammation and scarring of liver, spleen, and other organs where cysts develop<\/td>\r\n<td>Snail hosts release cercaria into freshwater; cercaria burrow into skin of swimmers and bathers<\/td>\r\n<td>Eggs in stool or urine, tissue biopsy, serological testing<\/td>\r\n<td>Praziquantel<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<\/div>\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Key Concepts and Summary<\/h3>\r\n<ul>\r\n \t<li><strong>Malaria<\/strong> is a protozoan parasite that remains an important cause of death primarily in the tropics. Several species in the genus <em>Plasmodium<\/em> are responsible for malaria and all are transmitted by <em>Anopheles<\/em> mosquitoes. <em>Plasmodium<\/em> infects and destroys human red blood cells, leading to organ damage, anemia, blood vessel necrosis, and death. Malaria can be treated with various antimalarial drugs and prevented through vector control.<\/li>\r\n \t<li><strong>Toxoplasmosis<\/strong> is a widespread protozoal infection that can cause serious infections in the immunocompromised and in developing fetuses. Domestic cats are the definitive host.<\/li>\r\n \t<li>Babesiosis is a generally asymptomatic infection of red blood cells that can causes malaria-like symptoms in elderly, immunocompromised, or asplenic patients.<\/li>\r\n \t<li><strong>Chagas disease<\/strong> is a tropical disease transmitted by triatomine bugs. The trypanosome infects heart, neural tissues, monocytes, and phagocytes, often remaining latent for many years before causing serious and sometimes fatal damage to the digestive system and heart.<\/li>\r\n \t<li><strong>Leishmaniasis<\/strong> is caused by the protozoan <em>Leishmania<\/em> and is transmitted by sand flies. Symptoms are generally mild, but serious cases may cause organ damage, anemia, and loss of immune competence.<\/li>\r\n \t<li><strong>Schistosomiasis<\/strong> is caused by a fluke transmitted by snails. The fluke moves throughout the body in the blood stream and chronically infects various tissues, leading to organ damage.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<div class=\"textbox exercises\">\r\n<h3>Multiple Choice<\/h3>\r\nWhich of the following diseases is caused by a helminth?\r\n<ol style=\"list-style-type: lower-alpha\">\r\n \t<li>leishmaniasis<\/li>\r\n \t<li>malaria<\/li>\r\n \t<li>Chagas disease<\/li>\r\n \t<li>schistosomiasis<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"170951\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"170951\"]Answer d. Schistosomiasis is caused by a helminth.[\/hidden-answer]\r\n\r\nWhich of these is the most common form of leishmaniasis?\r\n<ol style=\"list-style-type: lower-alpha\">\r\n \t<li>cutaneous<\/li>\r\n \t<li>mucosal<\/li>\r\n \t<li>visceral<\/li>\r\n \t<li>intestinal<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"827041\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"827041\"]Answer a. The most common form of leishmaniasis is\u00a0cutaneous.[\/hidden-answer]\r\n\r\nWhich of the following is a causative agent of malaria?\r\n<ol style=\"list-style-type: lower-alpha\">\r\n \t<li><em>Trypanosoma cruzi<\/em><\/li>\r\n \t<li><em>Toxoplasma gondii<\/em><\/li>\r\n \t<li><em>Plasmodium falciparum<\/em><\/li>\r\n \t<li><em>Schistosoma mansoni<\/em><\/li>\r\n<\/ol>\r\n[reveal-answer q=\"106665\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"106665\"]Answer c.\u00a0<em>Plasmodium falciparum<\/em>\u00a0is a causative agent of malaria.[\/hidden-answer]\r\n\r\nWhich of the following diseases does not involve an arthropod vector?\r\n<ol style=\"list-style-type: lower-alpha\">\r\n \t<li>schistosomiasis<\/li>\r\n \t<li>malaria<\/li>\r\n \t<li>Chagas disease<\/li>\r\n \t<li>babesiosis<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"829049\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"829049\"]Answer a. Schistosomiasis\u00a0does not involve an arthropod vector.[\/hidden-answer]\r\n\r\n<\/div>\r\n<div class=\"textbox exercises\">\r\n<h3>Fill in the Blank<\/h3>\r\nThe ________ mosquito is the biological vector for malaria.\r\n\r\n[reveal-answer q=\"893814\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"893814\"]The <strong><em>Anopheles<\/em><\/strong> mosquito is the biological vector for malaria.[\/hidden-answer]\r\n\r\nThe kissing bug is the biological vector for ________.\r\n\r\n[reveal-answer q=\"230395\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"230395\"]The kissing bug is the biological vector for <strong>Chagas disease<\/strong>.[\/hidden-answer]\r\n\r\nCercarial dermatitis is also known as ________.\r\n\r\n[reveal-answer q=\"941192\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"941192\"]Cercarial dermatitis is also known as <strong>swimmer\u2019s itch<\/strong>.[\/hidden-answer]\r\n\r\n<\/div>\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Think about It<\/h3>\r\n<ol>\r\n \t<li>Describe main cause of <em>Plasmodium falciparum<\/em> infection symptoms.<\/li>\r\n \t<li>Why should pregnant women avoid cleaning their cat\u2019s litter box or do so with protective gloves?<\/li>\r\n \t<li>What measures can be taken to reduce the likelihood of malaria reemerging in the US?<\/li>\r\n<\/ol>\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Objectives<\/h3>\n<ul>\n<li>Identify common parasites that cause infections of the circulatory and lymphatic systems<\/li>\n<li>Compare the major characteristics of specific parasitic diseases affecting the circulatory and lymphatic systems<\/li>\n<\/ul>\n<\/div>\n<p>Some protozoa and parasitic flukes are also capable of causing infections of the human circulatory system. Although these infections are rare in the US, they continue to cause widespread suffering in the developing world today. Fungal infections of the circulatory system are very rare. Therefore, they are not discussed in this chapter.<\/p>\n<h2>Malaria<\/h2>\n<p>Despite more than a century of intense research and clinical advancements, <strong>malaria<\/strong> remains one of the most important infectious diseases in the world today. Its widespread distribution places more than half of the world\u2019s population in jeopardy. In 2015, the WHO estimated there were about 214 million cases of malaria worldwide, resulting in about 438,000 deaths; about 88% of cases and 91% of deaths occurred in Africa.<a class=\"footnote\" title=\"World Health Organization. &quot;World Malaria Report 2015: Summary.&quot; 2015. http:\/\/www.who.int\/malaria\/publications\/world-malaria-report-2015\/report\/en\/. Accessed July 28, 2016.\" id=\"return-footnote-1101-1\" href=\"#footnote-1101-1\" aria-label=\"Footnote 1\"><sup class=\"footnote\">[1]<\/sup><\/a> Although malaria is not currently a major threat in the US, the possibility of its reintroduction is a concern. Malaria is caused by several protozoan parasites in the genus <strong><em>Plasmodium<\/em><\/strong>: <em>P. falciparum, P. knowlesi, P. malariae, P. ovale,<\/em> and <em>P. vivax. Plasmodium<\/em> primarily infect red blood cells and are transmitted through the bite of <strong><em>Anopheles<\/em> mosquitoes<\/strong>.<\/p>\n<p>Currently, <em>P. falciparum<\/em> is the most common and most lethal cause of malaria, often called falciparum malaria. Falciparum malaria is widespread in highly populated regions of Africa and Asia, putting many people at risk for the most severe form of the disease.<\/p>\n<p>The classic signs and symptoms of malaria are cycles of extreme fever and chills. The sudden, violent symptoms of malaria start with malaise, abrupt chills, and fever (39\u201341\u00b0 C [102.2\u2013105.8 \u00b0F]), rapid and faint pulse, polyuria, headache, myalgia, nausea, and vomiting. After 2 to 6 hours of these symptoms, the fever falls, and profuse sweating occurs for 2 to 3 hours, followed by extreme fatigue. These symptoms are a result of <em>Plasmodium<\/em> emerging from red blood cells synchronously, leading to simultaneous rupture of a large number of red blood cells, resulting in damage to the spleen, liver, lymph nodes, and bone marrow. The organ damage resulting from hemolysis causes patients to develop sludge blood (i.e., blood in which the red blood cells agglutinate into clumps) that can lead to lack of oxygen, necrosis of blood vessels, organ failure, and death.<\/p>\n<p>In established infections, malarial cycles of fever and chills typically occur every 2 days in the disease described as <strong>tertian malaria<\/strong>, which is caused by <em>P. vivax<\/em> and <em>P. ovale<\/em>. The cycles occur every 3 days in the disease described as <strong>quartan malaria<\/strong>, which is caused by <em>P. malariae<\/em>. These intervals may vary among cases.<\/p>\n<p><em>Plasmodium<\/em> has a complex life cycle that includes several developmental stages alternately produced in mosquitoes and humans (Figure\u00a01). When an infected mosquito takes a blood meal, sporozoites in the mosquito salivary gland are injected into the host\u2019s blood. These parasites circulate to the liver, where they develop into schizonts. The schizonts then undergo <strong>schizogony<\/strong>, resulting in the release of many merozoites at once. The merozoites move to the bloodstream and infect red blood cells. Inside red blood cells, merozoites develop into trophozoites that produce more merozoites. The synchronous release of merozoites from red blood cells in the evening leads to the symptoms of malaria.<\/p>\n<div style=\"width: 1310px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03175823\/OSC_Microbio_25_04_Malaria.jpg\" alt=\"Life cycle of Plasmodium. [Human Liver Stages] 1 \u2013 Mosquito take a blood meal and injects Plasmodium into a human. 2 \u2013 Plasmodium infects liver cell. 3 \u2013 Plasmodium multiplies in liver cell. [Human Blood Stages] 4 \u2013 Plasmodium enters blood. An immature ring stage looks like a signet ring in a red blood cell. This becomes a mature ring stage and undergoes mitosis to produce schizonts which are released by rupturing the red blood cells. 5 \u2013 Gametes (1n) produced by meiosis. [Mosquito Stages] 6 - Moquito takes a blood meal and ingests gametes. 7 \u2013 Microgametes fertilizes macrogamete. 8 \u2013 Zygote (2n) forms. 9 \u2013 Zygote undergoes mitosis. 10 \u2013 Parasite differentiates and enters the saliva of the mosquito.\" width=\"1300\" height=\"872\" \/><\/p>\n<p class=\"wp-caption-text\">Figure\u00a01. The life cycle of <em>Plasmodium<\/em>. (credit: modification of work by Centers for Disease Control and Prevention)<\/p>\n<\/div>\n<div style=\"width: 409px\" class=\"wp-caption alignright\"><img loading=\"lazy\" decoding=\"async\" class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03175827\/OSC_Microbio_25_04_BloodSmear.jpg\" alt=\"A micrograph showing red blood cells. A dark ring in the center of one cell is labeled ring form. A larger dark region in another cell is labeled schizont.\" width=\"399\" height=\"254\" \/><\/p>\n<p class=\"wp-caption-text\">Figure\u00a02. A blood smear (human blood stage) shows an early trophozoite in a delicate ring form (upper left) and an early stage schizont form (center) of Plasmodium falciparum from a patient with malaria. (credit: modification of work by Centers for Disease Control and Prevention)<\/p>\n<\/div>\n<p>In addition, some trophozoites alternatively develop into male and female gametocytes. The gametocytes are taken up when the mosquito takes a blood meal from an infected individual. Sexual sporogony occurs in the gut of the mosquito. The gametocytes fuse to form zygotes in the insect gut. The zygotes become motile and elongate into an ookinete. This form penetrates the midgut wall and develops into an oocyst. Finally, the oocyst releases new sporozoites that migrate to the mosquito salivary glands to complete the life cycle.<\/p>\n<p>Diagnosis of malaria is by microscopic observation of developmental forms of <em>Plasmodium<\/em> in blood smears and rapid EIA assays that detect <em>Plasmodium<\/em> antigens or enzymes (Figure\u00a02). Drugs such as <strong>chloroquine<\/strong>, <strong>atovaquone<\/strong> , <strong>artemether<\/strong>, and <strong>lumefantrine<\/strong> may be prescribed for both acute and prophylactic therapy, although some <em>Plasmodium<\/em> spp. have shown resistance to antimalarial drugs. Use of insecticides and insecticide-treated bed nets can limit the spread of malaria. Despite efforts to develop a vaccine for malaria, none is currently available.<\/p>\n<div class=\"textbox\">Visit this site to <a href=\"https:\/\/www.animalplanet.com\/tv-shows\/monsters-inside-me\/videos\/malaria-parasite\/\" target=\"_blank\" rel=\"noopener\">learn how the parasite <em>Plasmodium<\/em> infects red blood cells<\/a>.<\/div>\n<div class=\"textbox\">The <a href=\"http:\/\/nothingbutnets.net\/\" target=\"_blank\" rel=\"noopener\">Nothing But Nets campaign<\/a>, an initiative of the United Nations Foundation, has partnered with the Bill and Melinda Gates Foundation to make mosquito bed nets available in developing countries in Africa.<\/div>\n<h2>Toxoplasmosis<\/h2>\n<p>The disease <strong>toxoplasmosis<\/strong> is caused by the protozoan <strong><em>Toxoplasma gondii<\/em><\/strong>. <em>T. gondii<\/em> is found in a wide variety of birds and mammals,<a class=\"footnote\" title=\"A.M. Tenter et al.. &quot;Toxoplasma gondii: From Animals to Humans.&quot; International Journal for Parasitology 30 no. 12-13 (2000):1217\u20131258.\" id=\"return-footnote-1101-2\" href=\"#footnote-1101-2\" aria-label=\"Footnote 2\"><sup class=\"footnote\">[2]<\/sup><\/a> and human infections are common. The Centers for Disease Control and Prevention (CDC) estimates that 22.5% of the population 12 years and older has been infected with <em>T. gondii<\/em>; but immunocompetent individuals are typically asymptomatic, however.<a class=\"footnote\" title=\"Centers for Disease Control and Prevention. &quot;Parasites - Toxoplasmosis (Toxoplasma Infection). Epidemiology &amp; Risk Factors.&quot; 2015 http:\/\/www.cdc.gov\/parasites\/toxoplasmosis\/epi.html. Accessed July 28, 2016.\" id=\"return-footnote-1101-3\" href=\"#footnote-1101-3\" aria-label=\"Footnote 3\"><sup class=\"footnote\">[3]<\/sup><\/a> Domestic cats are the only known definitive hosts for the sexual stages of <em>T. gondii<\/em> and, thus, are the main reservoirs of infection. Infected cats shed <em>T. gondii<\/em> oocysts in their feces, and these oocysts typically spread to humans through contact with fecal matter on cats\u2019 bodies, in litter boxes, or in garden beds where outdoor cats defecate.<\/p>\n<p><em>T. gondii<\/em> has a complex <strong>life cycle<\/strong> that involves multiple hosts. The <em>T. gondii<\/em> life cycle begins when unsporulated oocysts are shed in the cat\u2019s feces. These oocysts take 1\u20135 days to sporulate in the environment and become infective. Intermediate hosts in nature include birds and rodents, which become infected after ingesting soil, water, or plant material contaminated with the infective oocysts. Once ingested<em>,<\/em> the oocysts transform into tachyzoites that localize in the bird or rodent neural and muscle tissue, where they develop into tissue cysts. Cats may become infected after consuming birds and rodents harboring tissue cysts. Cats and other animals may also become infected directly by ingestion of sporulated oocysts in the environment. Interestingly, <em>Toxoplasma<\/em> infection appears to be able to modify the host\u2019s behavior. Mice infected by <em>Toxoplasma<\/em> lose their fear of cat pheromones. As a result, they become easier prey for cats, facilitating the transmission of the parasite to the cat definitive host<a class=\"footnote\" title=\"J. Flegr. &quot;Effects of Toxoplasma on Human Behavior.&quot; Schizophrenia Bulletin 33, no. 3 (2007):757\u2013760.\" id=\"return-footnote-1101-4\" href=\"#footnote-1101-4\" aria-label=\"Footnote 4\"><sup class=\"footnote\">[4]<\/sup><\/a> (Figure\u00a03).<\/p>\n<div style=\"width: 1310px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03175833\/OSC_Microbio_25_04_Toxoplasma.jpg\" alt=\"Life cycle of Toxoplasma gondii. 1 - Insporulated oocysts are shed in the cat\u2019s feces. 2 \u2013 Intermediate host in nature (including birds and rodents) become infected after ingesting soil, water or plant material contaminated with oocysts. 3 \u2013 Oocysts transform into tachyzoites shortly after ingestion. These tachyzoites localize in neural and muscle tissue and develop into tissue cyst bradyzoites. 4 - Cats eat infected animals (such as rodents or birsds) and shed unsporulated oocysts. 5 \u2013 Intermediate hosts (such as pigs and cows) ingeset oocysts from contaminated water, soil, or plant material. 6 \u2013 Humans can become infected when they eat undercooked meat of infected animals harboring tissue cysts. 7 \u2013 Humans can also become infected when they consume food or water contaminate with cat feces or by handling fecal-contaminated soil or cat\u2019s litter box. 8 \u2013 Humans can also become infected via the placenta from fetus to mother. 10 \u2013 Tissue cysts can form in skeletal muscle, myocardium, brain, and eyes. 11 \u2013 Diagnosis of congenital infection can be achieved by detecting T. gondii DNA in amniotic fluid using molecular methods such as PCR.\" width=\"1300\" height=\"1310\" \/><\/p>\n<p class=\"wp-caption-text\">Figure\u00a03. The infectious cycle of <em>Toxoplasma gondii<\/em>. (credit: &#8220;diagram&#8221;: modification of work by Centers for Disease Control and Prevention; credit &#8220;cat&#8221;: modification of work by &#8220;KaCey97078&#8243;\/Flickr)<\/p>\n<\/div>\n<p><em>Toxoplasma<\/em> infections in humans are extremely common, but most infected people are asymptomatic or have subclinical symptoms. Some studies suggest that the parasite may be able to influence the personality and psychomotor performance of infected humans, similar to the way it modifies behavior in other mammals.<a class=\"footnote\" title=\"Ibid.\" id=\"return-footnote-1101-5\" href=\"#footnote-1101-5\" aria-label=\"Footnote 5\"><sup class=\"footnote\">[5]<\/sup><\/a> When symptoms do occur, they tend to be mild and similar to those of mononucleosis. However, asymptomatic toxoplasmosis can become problematic in certain situations. Cysts can lodge in a variety of human tissues and lie dormant for years. Reactivation of these quiescent infections can occur in immunocompromised patients following transplantation, cancer therapy, or the development of an immune disorder such as <strong>AIDS<\/strong>. In patients with AIDS who have toxoplasmosis, the immune system cannot combat the growth of <em>T. gondii<\/em> in body tissues; as a result, these cysts can cause encephalitis, retinitis, pneumonitis, cognitive disorders, and seizures that can eventually be fatal.<\/p>\n<p>Toxoplasmosis can also pose a risk during <strong>pregnancy<\/strong> because tachyzoites can cross the placenta and cause serious infections in the developing fetus. The extent of fetal damage resulting from toxoplasmosis depends on the severity of maternal disease, the damage to the placenta, the gestational age of the fetus when infected, and the virulence of the organism. Congenital toxoplasmosis often leads to fetal loss or premature birth and can result in damage to the central nervous system, manifesting as mental retardation, deafness, or blindness. Consequently, pregnant women are advised by the CDC to take particular care in preparing meat, gardening, and caring for pet cats.<a class=\"footnote\" title=\"Centers for Disease Control and Prevention. &quot;Parasites - Toxoplasmosis (Toxoplasma infection). Toxoplasmosis Frequently Asked Questions (FAQs).&quot; 2013. http:\/\/www.cdc.gov\/parasites\/toxoplasmosis\/gen_info\/faqs.html. Accessed July 28, 2016.\" id=\"return-footnote-1101-6\" href=\"#footnote-1101-6\" aria-label=\"Footnote 6\"><sup class=\"footnote\">[6]<\/sup><\/a> Diagnosis of toxoplasmosis infection during pregnancy is usually achieved by serology including <strong>TORCH<\/strong> testing (the &#8220;T&#8221; in TORCH stands for toxoplasmosis). Diagnosis of congenital infections can also be achieved by detecting <em>T. gondii<\/em> DNA in amniotic fluid, using molecular methods such as PCR.<\/p>\n<p>In adults, diagnosis of toxoplasmosis can include observation of tissue cysts in tissue specimens. Tissue cysts may be observed in Giemsa- or Wright-stained biopsy specimens, and CT, magnetic resonance imaging, and lumbar puncture can also be used to confirm infection (Figure\u00a04).<\/p>\n<p>Preventing infection is the best first-line defense against toxoplasmosis. Preventive measures include washing hands thoroughly after handling raw meat, soil, or cat litter, and avoiding consumption of vegetables possibly contaminated with cat feces. All meat should be cooked to an internal temperature of 73.9\u201376.7 \u00b0C (165\u2013170 \u00b0F).<\/p>\n<p>Most immunocompetent patients do not require clinical intervention for <em>Toxoplasma<\/em> infections. However, neonates, pregnant women, and immunocompromised patients can be treated with <strong>pyrimethamine<\/strong> and <strong>sulfadiazine<\/strong>\u2014except during the first trimester of pregnancy, because these drugs can cause birth defects. <strong>Spiramycin<\/strong> has been used safely to reduce transmission in pregnant women with primary infection during the first trimester because it does not cross the placenta.<\/p>\n<div style=\"width: 910px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03175836\/OSC_Microbio_25_04_SabinFeld.jpg\" alt=\"A) A micrograph of curved cells with a nucleus. B) micrograph of a sphere with many smaller spheres inside.\" width=\"900\" height=\"383\" \/><\/p>\n<p class=\"wp-caption-text\">Figure\u00a04. (a) Giemsa-stained <em>Toxoplasma gondii<\/em> tachyzoites from a smear of peritoneal fluid obtained from a mouse inoculated with <em>T. gondii<\/em>. Tachyzoites are typically crescent shaped with a prominent, centrally placed nucleus. (b) Microscopic cyst containing <em>T. gondii<\/em> from mouse brain tissue. Thousands of resting parasites (stained red) are contained in a thin parasite cyst wall. (credit a: modification of work by Centers for Disease Control and Prevention; credit b: modification of work by USDA)<\/p>\n<\/div>\n<h2>Babesiosis<\/h2>\n<p>Babesiosis is a rare zoonotic infectious disease caused by <strong><em>Babesia<\/em> spp<\/strong>. These parasitic protozoans infect various wild and domestic animals and can be transmitted to humans by black-legged <em>Ixodes<\/em> ticks. In humans, <em>Babesia<\/em> infect red blood cells and replicate inside the cell until it ruptures. The <em>Babesia<\/em> released from the ruptured red blood cell continue the growth cycle by invading other red blood cells. Patients may be asymptomatic, but those who do have symptoms often initially experience malaise, fatigue, chills, fever, headache, myalgia, and arthralgia. In rare cases, particularly in asplenic (absence of the spleen) patients, the elderly, and patients with <strong>AIDS<\/strong>, <strong>babesiosis<\/strong> may resemble falciparum malaria, with high fever, hemolytic anemia, hemoglobinuria (hemoglobin or blood in urine), jaundice, and renal failure, and the infection can be fatal. Previously acquired asymptomatic Babesia infection may become symptomatic if a splenectomy is performed.<\/p>\n<div style=\"width: 460px\" class=\"wp-caption alignright\"><img loading=\"lazy\" decoding=\"async\" class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03175838\/OSC_Microbio_25_04_babesia.jpg\" alt=\"Micrograph of red blood cells with dark circles inside.\" width=\"450\" height=\"270\" \/><\/p>\n<p class=\"wp-caption-text\">Figure\u00a05. In this blood smear from a patient with babesiosis, <em>Babesia<\/em> parasites can be observed in the red blood cells. (credit: modification of work by Centers for Disease Control and Prevention)<\/p>\n<\/div>\n<p>Diagnosis is based mainly on the microscopic observation of parasites in blood smears (Figure\u00a05). Serologic and antibody detection by IFA can also be performed and PCR-based tests are available. Many people do not require clinical intervention for Babesia infections, however, serious infections can be cleared with a combination of <strong>atovaquone<\/strong> and <strong>azithromycin<\/strong> or a combination of <strong>clindamycin<\/strong> and <strong>quinine<\/strong>.<\/p>\n<h2>Chagas Disease<\/h2>\n<p>Also called <strong>American trypanosomiasis<\/strong>, Chagas disease is a zoonosis classified as a <strong>neglected tropical disease<\/strong> (NTD). It is caused by the flagellated protozoan <strong><em>Trypanosoma cruzi<\/em><\/strong> and is most commonly transmitted to animals and people through the feces of triatomine bugs. The <strong>triatomine bug<\/strong> is nicknamed the kissing bug because it frequently bites humans on the face or around the eyes; the insect often defecates near the bite and the infected fecal matter may be rubbed into the bite wound by the bitten individual (Figure\u00a06). The bite itself is painless and, initially, many people show no signs of the disease. Alternative modes of transmission include contaminated blood transfusions, organ transplants from infected donors, and congenital transmission from mother to fetus.<\/p>\n<p>Chagas disease is endemic throughout much of Mexico, Central America, and South America, where, according to WHO, an estimated 6 million to 7 million people are infected.<a class=\"footnote\" title=\"World Health Organization. &quot;Chagas disease (American trypanosomiasis). Fact Sheet.&quot; 2016. http:\/\/www.who.int\/mediacentre\/factsheets\/fs340\/en\/. Accessed July 29, 2016.\" id=\"return-footnote-1101-7\" href=\"#footnote-1101-7\" aria-label=\"Footnote 7\"><sup class=\"footnote\">[7]<\/sup><\/a> Currently, Chagas disease is not endemic in the US, even though triatomine bugs are found in the southern half of the country.<\/p>\n<p>Triatomine bugs typically are active at night, when they take blood meals by biting the faces and lips of people or animals as they sleep and often defecate near the site of the bite. Infection occurs when the host rubs the feces into their eyes, mouth, the bite wound, or another break in the skin. The protozoan then enters the blood and invades tissues of the heart and central nervous system, as well as macrophages and monocytes. Nonhuman reservoirs of <em>T. cruzi<\/em> parasites include wild animals and domesticated animals such as dogs and cats, which also act as reservoirs of the pathogen.<a class=\"footnote\" title=\"C.E. Reisenman et al. &quot;Infection of Kissing Bugs With Trypanosoma cruzi, Tucson, Arizona, USA.&quot; Emerging Infectious Diseases 16 no. 3 (2010):400\u2013405.\" id=\"return-footnote-1101-8\" href=\"#footnote-1101-8\" aria-label=\"Footnote 8\"><sup class=\"footnote\">[8]<\/sup><\/a><\/p>\n<p>There are three phases of Chagas disease: acute, intermediate, and chronic. These phases can be either asymptomatic or life-threatening depending on the immunocompetence status of the patient.<\/p>\n<p>In acute phase disease, symptoms include fever, headache, myalgia, rash, vomiting, diarrhea, and enlarged spleen, liver, and lymph nodes. In addition, a localized nodule called a chagoma may form at the portal of entry, and swelling of the eyelids or the side of the face, called Roma\u00f1a&#8217;s sign, may occur near the bite wound. Symptoms of the acute phase may resolve spontaneously, but if untreated, the infection can persist in tissues, causing irreversible damage to the heart or brain. In rare cases, young children may die of <strong>myocarditis<\/strong> or <strong>meningoencephalitis<\/strong> during the acute phase of Chagas disease.<\/p>\n<p>Following the acute phase is a prolonged intermediate phase during which few or no parasites are found in the blood and most people are asymptomatic. Many patients will remain asymptomatic for life; however, decades after exposure, an estimated 20%\u201330% of infected people will develop chronic disease that can be debilitating and sometimes life threatening. In the chronic phase, patients may develop painful swelling of the colon, leading to severe twisting, constipation, and bowel obstruction; painful swelling of the esophagus, leading to dysphagia and malnutrition; and <strong>flaccid cardiomegaly<\/strong> (enlargement of the heart), which can lead to heart failure and sudden death.<\/p>\n<p>Diagnosis can be confirmed through several different tests, including direct microscopic observation of trypanosomes in the blood, IFA, EIAs, PCR, and culturing in artificial media. In endemic regions, xenodiagnoses may be used; this method involves allowing uninfected kissing bugs to feed on the patient and then examining their feces for the presence of <em>T. cruzi<\/em>.<\/p>\n<p>The medications <strong>nifurtimox<\/strong> and <strong>benznidazole<\/strong> are effective treatments during the acute phase of Chagas disease. The efficacy of these drugs is much lower when the disease is in the chronic phase. Avoiding exposure to the pathogen through vector control is the most effective method of limiting this disease.<\/p>\n<div style=\"width: 1210px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03175842\/OSC_Microbio_25_04_Trypanosom.jpg\" alt=\"a) Micrograph of red blood cells with crescent-shaped cells outside. These parasitic cells are about the length of 2 red blood cells. B) photo of a triatomine bug.\" width=\"1200\" height=\"547\" \/><\/p>\n<p class=\"wp-caption-text\">Figure\u00a06. (a) <em>Trypanosoma cruzi<\/em> protozoan in a blood smear from a patient with Chagas disease. (b) The triatomine bug (also known as the kissing bug or assassin bug) is the vector of Chagas disease. (credit a: modification of work by Centers for Disease Control and Prevention; credit b: modification of work by Erwin Huebner)<\/p>\n<\/div>\n<h2>Leishmaniasis<\/h2>\n<p>Although it is classified as an NTD, <strong>leishmaniasis<\/strong> is relatively widespread in tropical and subtropical regions, affecting people in more than 90 countries. It is caused by approximately 20 different species of <strong><em>Leishmania<\/em><\/strong>, protozoan parasites that are transmitted by <strong>sand fly<\/strong> vectors such as <em>Phlebotomus<\/em> spp. and <em>Lutzomyia<\/em> spp. Dogs, cats, sheep, horses, cattle rodents, and humans can all serve as reservoirs.<\/p>\n<p>The <em>Leishmania<\/em> protozoan is phagocytosed by macrophages but uses virulence factors to avoid destruction within the phagolysosome. The virulence factors inhibit the phagolysosome enzymes that would otherwise destroy the parasite. The parasite reproduces within the macrophage, lyses it, and the progeny infect new macrophages (see <a href=\".\/chapter\/pathogen-recognition-and-phagocytosis\/\" target=\"_blank\" rel=\"noopener\">&#8220;When Phagocytosis Fails&#8221; in\u00a0Pathogen Recognition and Phagocytosis<\/a>).<\/p>\n<p>The three major clinical forms of leishmaniasis are cutaneous (oriental sore, Delhi boil, Aleppo boil), visceral (kala-azar, Dumdum fever), and mucosal (espundia). The most common form of disease is <strong>cutaneous leishmaniasis<\/strong>, which is characterized by the formation of sores at the site of the insect bite that may start out as papules or nodules before becoming large ulcers (Figure\u00a07).<\/p>\n<p>It may take <strong>visceral leishmaniasis<\/strong> months and sometimes years to develop, leading to enlargement of the lymph nodes, liver, spleen, and bone marrow. The damage to these body sites triggers fever, weight loss, and swelling of the spleen and liver. It also causes a decrease in the number of red blood cells (anemia), white blood cells (leukopenia), and platelets (thrombocytopenia), causing the patient to become immunocompromised and more susceptible to fatal infections of the lungs and gastrointestinal tract.<\/p>\n<p>The mucosal form of leishmaniasis is one of the less common forms of the disease. It causes a lesion similar to the cutaneous form but <strong>mucosal leishmaniasis<\/strong> is associated with mucous membranes of the mouth, nares, or pharynx, and can be destructive and disfiguring. Mucosal leishmaniasis occurs less frequently when the original cutaneous (skin) infection is promptly treated.<\/p>\n<p>Definitive diagnosis of leishmaniasis is made by visualizing organisms in Giemsa-stained smears, by isolating <em>Leishmania<\/em> protozoans in cultures, or by PCR-based assays of aspirates from infected tissues. Specific DNA probes or analysis of cultured parasites can help to distinguish <em>Leishmania<\/em> species that are causing simple cutaneous leishmaniasis from those capable of causing mucosal leishmaniasis.<\/p>\n<p>Cutaneous leishmaniasis is usually not treated. The lesions will resolve after weeks (or several months), but may result in scarring. Recurrence rates are low for this disease. More serious infections can be treated with <strong>stibogluconate<\/strong> (antimony gluconate), <strong>amphotericin B<\/strong>, and <strong>miltefosine<\/strong>.<\/p>\n<div style=\"width: 1310px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03175846\/OSC_Microbio_25_04_Leishmania.jpg\" alt=\"a) Micrograph of a tissue sample. A black arrow points to leishmania mexicana. B) a large, open wound on skin.\" width=\"1300\" height=\"680\" \/><\/p>\n<p class=\"wp-caption-text\">Figure\u00a07. (a) A micrograph of a tissue sample from a patient with localized cutaneous leishmaniasis. Parasitic <em>Leishmania mexicana<\/em> (black arrow) are visible in and around the host cells. (b) Large skin ulcers are associated with cutaneous leishmaniasis. (credit a: modification of work by Fern\u00e1ndez-Figueroa EA, Rangel-Escare\u00f1o C, Espinosa-Mateos V, Carrillo-S\u00e1nchez K, Salaiza-Suazo N, Carrada-Figueroa G, March-Mifsut S, and Becker I; credit b: modification of work by Jean Fortunet)<\/p>\n<\/div>\n<h2>Schistosomiasis<\/h2>\n<p>Schistosomiasis (bilharzia) is an NTD caused by blood flukes in the genus <strong><em>Schistosoma<\/em><\/strong> that are native to the Caribbean, South America, Middle East, Asia, and Africa. Most human <strong>schistosomiasis<\/strong> cases are caused by <em>Schistosoma mansoni, S. haematobium<\/em>, or <em>S. japonicum<\/em>. <em>Schistosoma<\/em> are the only <strong>trematodes<\/strong> that invade through the skin; all other trematodes infect by ingestion. WHO estimates that at least 258 million people required preventive treatment for schistosomiasis in 2014.<a class=\"footnote\" title=\"World Health Organization. &quot;Schistosomiasis. Fact Sheet.&quot; 2016. http:\/\/www.who.int\/mediacentre\/factsheets\/fs115\/en\/. Accessed July 29, 2016.\" id=\"return-footnote-1101-9\" href=\"#footnote-1101-9\" aria-label=\"Footnote 9\"><sup class=\"footnote\">[9]<\/sup><\/a><\/p>\n<p>Infected human hosts shed <em>Schistosoma<\/em> eggs in urine and feces, which can contaminate freshwater habitats of snails that serve as intermediate hosts. The eggs hatch in the water, releasing miracidia, an intermediate growth stage of the <em>Schistosoma<\/em> that infect the snails. The miracidia mature and multiply inside the snails, transforming into cercariae that leave the snail and enter the water, where they can penetrate the skin of swimmers and bathers. The cercariae migrate through human tissue and enter the bloodstream, where they mature into adult male and female worms that mate and release fertilized eggs. The eggs travel through the bloodstream and penetrate various body sites, including the bladder or intestine, from which they are excreted in urine or stool to start the life cycle over again (<a href=\".\/chapter\/parasitic-helminths\/\" target=\"_blank\" rel=\"noopener\">Figure\u00a04 in\u00a0Parasitic Helminths<\/a>).<\/p>\n<p>A few days after infection, patients may develop a rash or itchy skin associated with the site of cercariae penetration. Within 1\u20132 months of infection, symptoms may develop, including fever, chills, cough, and myalgia, as eggs that are not excreted circulate through the body. After years of infection, the eggs become lodged in tissues and trigger inflammation and scarring that can damage the liver, central nervous system, intestine, spleen, lungs, and bladder. This may cause abdominal pain, enlargement of the liver, blood in the urine or stool, and problems passing urine. Increased risk for bladder cancer is also associated with chronic <em>Schistosoma<\/em> infection. In addition, children who are repeatedly infected can develop malnutrition, anemia, and learning difficulties.<\/p>\n<p>Diagnosis of schistosomiasis is made by the microscopic observation of eggs in feces or urine, intestine or bladder tissue specimens, or serologic tests. The drug <strong>praziquantel<\/strong> is effective for the treatment of all schistosome infections. Improving wastewater management and educating at-risk populations to limit exposure to contaminated water can help control the spread of the disease.<\/p>\n<h3>Cercarial Dermatitis<\/h3>\n<p>The cercaria of some species of <em>Schistosoma<\/em> can only transform into adult worms and complete their life cycle in animal hosts such as migratory birds and mammals. The cercaria of these worms are still capable of penetrating human skin, but they are unable to establish a productive infection in human tissue. Still, the presence of the cercaria in small blood vessels triggers an immune response, resulting in itchy raised bumps called <strong>cercarial dermatitis<\/strong> (also known as swimmer\u2019s itch or clam digger&#8217;s itch). Although it is uncomfortable, cercarial dermatitis is typically self-limiting and rarely serious. Antihistamines and antipruritics can be used to limit inflammation and itching, respectively.<\/p>\n<div class=\"textbox shaded\">\n<h3>Common Eukaryotic Pathogens of the Human Circulatory System<\/h3>\n<p>Protozoan and helminthic infections are prevalent in the developing world. A few of the more important parasitic infections are summarized in Table 1.<\/p>\n<table>\n<thead>\n<tr>\n<th colspan=\"6\">Table 1.\u00a0Parasitic Diseases of the Circulatory and Lymphatic Systems<\/th>\n<\/tr>\n<tr>\n<th>Disease<\/th>\n<th>Pathogen<\/th>\n<th>Signs and Symptoms<\/th>\n<th>Transmission<\/th>\n<th>Diagnostic Tests<\/th>\n<th>Antimicrobial Drugs<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<th colspan=\"6\">Protozoa<\/th>\n<\/tr>\n<tr>\n<td>Babesiosis<\/td>\n<td><em>Babesia<\/em> spp.<\/td>\n<td>Malaise, chills, fever, headache, myalgia, arthralgia<\/td>\n<td>From animals to humans via <em>Ixodes<\/em> tick vectors<\/td>\n<td>Blood smear, serology, IFA, and PCR<\/td>\n<td>Atovaquone and azithromycin or clindamycin and quinine<\/td>\n<\/tr>\n<tr>\n<td>Chagas disease<\/td>\n<td><em>Trypanosoma cruzi<\/em><\/td>\n<td>Fever, headache, body aches, swollen lymph nodes; potentially fatal<\/td>\n<td>Between humans or from animal reservoirs via triatomine (kissing bug) vector<\/td>\n<td>Blood smear, IFA, EIA, PCR, xenodiagnoses<\/td>\n<td>Nifurtimox, benznidazole<\/td>\n<\/tr>\n<tr>\n<td>Leishmaniasis<\/td>\n<td><em>Leishmania<\/em> spp.<\/td>\n<td>Ulcer; enlargement of the lymph nodes, liver, spleen, and other organs<\/td>\n<td>Between humans or from animal reservoirs via sand fly (<em>Phlebotomus<\/em>\u00a0spp., <em>Lutzomyia<\/em>\u00a0spp.) vectors<\/td>\n<td>Blood smear, culture, PCR, DNA probe, biopsy<\/td>\n<td>Stibogluconate, amphotericin\u00a0B, miltefosine<\/td>\n<\/tr>\n<tr>\n<td>Malaria<\/td>\n<td><em>Plasmodium vivax, P.\u00a0malariae, P.\u00a0falciparum, P.\u00a0ovale, P.\u00a0knowlesi<\/em><\/td>\n<td>Extreme fever, chills, myalgia, nausea, and vomiting, possibly leading to organ failure and death<\/td>\n<td>Between humans via Anopheles mosquito vectors<\/td>\n<td>Blood smear, EIA<\/td>\n<td>Chloroquine, atovaquone, artemether, and lumefantrine<\/td>\n<\/tr>\n<tr>\n<td>Toxoplasmosis<\/td>\n<td><em>Toxoplasma gondii<\/em><\/td>\n<td>Tissue cysts; in pregnant women, birth defects or miscarriage<\/td>\n<td>Contact with feces of infected cat; eating contaminated vegetables or undercooked meat of infected animal<\/td>\n<td>Serological tests, direct detection of pathogen in tissue sections<\/td>\n<td>Sulfadiazine, pyrimethamine, spiramycin<\/td>\n<\/tr>\n<tr>\n<th colspan=\"6\">Helminths<\/th>\n<\/tr>\n<tr>\n<td>Schistosomiasis<\/td>\n<td><em>Schistosoma<\/em> spp.<\/td>\n<td>Rash, fever, chills, myalgia; chronic inflammation and scarring of liver, spleen, and other organs where cysts develop<\/td>\n<td>Snail hosts release cercaria into freshwater; cercaria burrow into skin of swimmers and bathers<\/td>\n<td>Eggs in stool or urine, tissue biopsy, serological testing<\/td>\n<td>Praziquantel<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<div class=\"textbox key-takeaways\">\n<h3>Key Concepts and Summary<\/h3>\n<ul>\n<li><strong>Malaria<\/strong> is a protozoan parasite that remains an important cause of death primarily in the tropics. Several species in the genus <em>Plasmodium<\/em> are responsible for malaria and all are transmitted by <em>Anopheles<\/em> mosquitoes. <em>Plasmodium<\/em> infects and destroys human red blood cells, leading to organ damage, anemia, blood vessel necrosis, and death. Malaria can be treated with various antimalarial drugs and prevented through vector control.<\/li>\n<li><strong>Toxoplasmosis<\/strong> is a widespread protozoal infection that can cause serious infections in the immunocompromised and in developing fetuses. Domestic cats are the definitive host.<\/li>\n<li>Babesiosis is a generally asymptomatic infection of red blood cells that can causes malaria-like symptoms in elderly, immunocompromised, or asplenic patients.<\/li>\n<li><strong>Chagas disease<\/strong> is a tropical disease transmitted by triatomine bugs. The trypanosome infects heart, neural tissues, monocytes, and phagocytes, often remaining latent for many years before causing serious and sometimes fatal damage to the digestive system and heart.<\/li>\n<li><strong>Leishmaniasis<\/strong> is caused by the protozoan <em>Leishmania<\/em> and is transmitted by sand flies. Symptoms are generally mild, but serious cases may cause organ damage, anemia, and loss of immune competence.<\/li>\n<li><strong>Schistosomiasis<\/strong> is caused by a fluke transmitted by snails. The fluke moves throughout the body in the blood stream and chronically infects various tissues, leading to organ damage.<\/li>\n<\/ul>\n<\/div>\n<div class=\"textbox exercises\">\n<h3>Multiple Choice<\/h3>\n<p>Which of the following diseases is caused by a helminth?<\/p>\n<ol style=\"list-style-type: lower-alpha\">\n<li>leishmaniasis<\/li>\n<li>malaria<\/li>\n<li>Chagas disease<\/li>\n<li>schistosomiasis<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q170951\">Show Answer<\/span><\/p>\n<div id=\"q170951\" class=\"hidden-answer\" style=\"display: none\">Answer d. Schistosomiasis is caused by a helminth.<\/div>\n<\/div>\n<p>Which of these is the most common form of leishmaniasis?<\/p>\n<ol style=\"list-style-type: lower-alpha\">\n<li>cutaneous<\/li>\n<li>mucosal<\/li>\n<li>visceral<\/li>\n<li>intestinal<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q827041\">Show Answer<\/span><\/p>\n<div id=\"q827041\" class=\"hidden-answer\" style=\"display: none\">Answer a. The most common form of leishmaniasis is\u00a0cutaneous.<\/div>\n<\/div>\n<p>Which of the following is a causative agent of malaria?<\/p>\n<ol style=\"list-style-type: lower-alpha\">\n<li><em>Trypanosoma cruzi<\/em><\/li>\n<li><em>Toxoplasma gondii<\/em><\/li>\n<li><em>Plasmodium falciparum<\/em><\/li>\n<li><em>Schistosoma mansoni<\/em><\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q106665\">Show Answer<\/span><\/p>\n<div id=\"q106665\" class=\"hidden-answer\" style=\"display: none\">Answer c.\u00a0<em>Plasmodium falciparum<\/em>\u00a0is a causative agent of malaria.<\/div>\n<\/div>\n<p>Which of the following diseases does not involve an arthropod vector?<\/p>\n<ol style=\"list-style-type: lower-alpha\">\n<li>schistosomiasis<\/li>\n<li>malaria<\/li>\n<li>Chagas disease<\/li>\n<li>babesiosis<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q829049\">Show Answer<\/span><\/p>\n<div id=\"q829049\" class=\"hidden-answer\" style=\"display: none\">Answer a. Schistosomiasis\u00a0does not involve an arthropod vector.<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox exercises\">\n<h3>Fill in the Blank<\/h3>\n<p>The ________ mosquito is the biological vector for malaria.<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q893814\">Show Answer<\/span><\/p>\n<div id=\"q893814\" class=\"hidden-answer\" style=\"display: none\">The <strong><em>Anopheles<\/em><\/strong> mosquito is the biological vector for malaria.<\/div>\n<\/div>\n<p>The kissing bug is the biological vector for ________.<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q230395\">Show Answer<\/span><\/p>\n<div id=\"q230395\" class=\"hidden-answer\" style=\"display: none\">The kissing bug is the biological vector for <strong>Chagas disease<\/strong>.<\/div>\n<\/div>\n<p>Cercarial dermatitis is also known as ________.<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q941192\">Show Answer<\/span><\/p>\n<div id=\"q941192\" class=\"hidden-answer\" style=\"display: none\">Cercarial dermatitis is also known as <strong>swimmer\u2019s itch<\/strong>.<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox key-takeaways\">\n<h3>Think about It<\/h3>\n<ol>\n<li>Describe main cause of <em>Plasmodium falciparum<\/em> infection symptoms.<\/li>\n<li>Why should pregnant women avoid cleaning their cat\u2019s litter box or do so with protective gloves?<\/li>\n<li>What measures can be taken to reduce the likelihood of malaria reemerging in the US?<\/li>\n<\/ol>\n<\/div>\n\n\t\t\t <section class=\"citations-section\" role=\"contentinfo\">\n\t\t\t <h3>Candela Citations<\/h3>\n\t\t\t\t\t <div>\n\t\t\t\t\t\t <div id=\"citation-list-1101\">\n\t\t\t\t\t\t\t <div class=\"licensing\"><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Shared previously<\/div><ul class=\"citation-list\"><li>OpenStax Microbiology. <strong>Provided by<\/strong>: OpenStax CNX. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"http:\/\/cnx.org\/contents\/e42bd376-624b-4c0f-972f-e0c57998e765@4.2\">http:\/\/cnx.org\/contents\/e42bd376-624b-4c0f-972f-e0c57998e765@4.2<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY: Attribution<\/a><\/em>. <strong>License Terms<\/strong>: Download for free at http:\/\/cnx.org\/contents\/e42bd376-624b-4c0f-972f-e0c57998e765@4.2<\/li><\/ul><\/div>\n\t\t\t\t\t\t <\/div>\n\t\t\t\t\t <\/div>\n\t\t\t <\/section><hr class=\"before-footnotes clear\" \/><div class=\"footnotes\"><ol><li id=\"footnote-1101-1\">World Health Organization. \"World Malaria Report 2015: Summary.\" 2015. http:\/\/www.who.int\/malaria\/publications\/world-malaria-report-2015\/report\/en\/. Accessed July 28, 2016. <a href=\"#return-footnote-1101-1\" class=\"return-footnote\" aria-label=\"Return to footnote 1\">&crarr;<\/a><\/li><li id=\"footnote-1101-2\">A.M. Tenter et al.. \"<em>Toxoplasma gondii<\/em>: From Animals to Humans.\" <em>International Journal for Parasitology<\/em> 30 no. 12-13 (2000):1217\u20131258. <a href=\"#return-footnote-1101-2\" class=\"return-footnote\" aria-label=\"Return to footnote 2\">&crarr;<\/a><\/li><li id=\"footnote-1101-3\">Centers for Disease Control and Prevention. \"Parasites - Toxoplasmosis (Toxoplasma Infection). Epidemiology &amp; Risk Factors.\" 2015 http:\/\/www.cdc.gov\/parasites\/toxoplasmosis\/epi.html. Accessed July 28, 2016. <a href=\"#return-footnote-1101-3\" class=\"return-footnote\" aria-label=\"Return to footnote 3\">&crarr;<\/a><\/li><li id=\"footnote-1101-4\">J. Flegr. \"Effects of <em>Toxoplasma<\/em> on Human Behavior.\" <em>Schizophrenia Bulletin<\/em> 33, no. 3 (2007):757\u2013760. <a href=\"#return-footnote-1101-4\" class=\"return-footnote\" aria-label=\"Return to footnote 4\">&crarr;<\/a><\/li><li id=\"footnote-1101-5\">Ibid. <a href=\"#return-footnote-1101-5\" class=\"return-footnote\" aria-label=\"Return to footnote 5\">&crarr;<\/a><\/li><li id=\"footnote-1101-6\">Centers for Disease Control and Prevention. \"Parasites - Toxoplasmosis (Toxoplasma infection). Toxoplasmosis Frequently Asked Questions (FAQs).\" 2013. http:\/\/www.cdc.gov\/parasites\/toxoplasmosis\/gen_info\/faqs.html. Accessed July 28, 2016. <a href=\"#return-footnote-1101-6\" class=\"return-footnote\" aria-label=\"Return to footnote 6\">&crarr;<\/a><\/li><li id=\"footnote-1101-7\">World Health Organization. \"Chagas disease (American trypanosomiasis). Fact Sheet.\" 2016. http:\/\/www.who.int\/mediacentre\/factsheets\/fs340\/en\/. Accessed July 29, 2016. <a href=\"#return-footnote-1101-7\" class=\"return-footnote\" aria-label=\"Return to footnote 7\">&crarr;<\/a><\/li><li id=\"footnote-1101-8\">C.E. Reisenman et al. \"Infection of Kissing Bugs With <em>Trypanosoma cruzi<\/em>, Tucson, Arizona, USA.\" <em>Emerging Infectious Diseases<\/em> 16 no. 3 (2010):400\u2013405. <a href=\"#return-footnote-1101-8\" class=\"return-footnote\" aria-label=\"Return to footnote 8\">&crarr;<\/a><\/li><li id=\"footnote-1101-9\">World Health Organization. \"Schistosomiasis. Fact Sheet.\" 2016. http:\/\/www.who.int\/mediacentre\/factsheets\/fs115\/en\/. Accessed July 29, 2016. <a href=\"#return-footnote-1101-9\" class=\"return-footnote\" aria-label=\"Return to footnote 9\">&crarr;<\/a><\/li><\/ol><\/div>","protected":false},"author":17,"menu_order":5,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"OpenStax Microbiology\",\"author\":\"\",\"organization\":\"OpenStax CNX\",\"url\":\"http:\/\/cnx.org\/contents\/e42bd376-624b-4c0f-972f-e0c57998e765@4.2\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Download for free at http:\/\/cnx.org\/contents\/e42bd376-624b-4c0f-972f-e0c57998e765@4.2\"}]","CANDELA_OUTCOMES_GUID":"","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-1101","chapter","type-chapter","status-publish","hentry"],"part":1066,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/pressbooks\/v2\/chapters\/1101","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/wp\/v2\/users\/17"}],"version-history":[{"count":5,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/pressbooks\/v2\/chapters\/1101\/revisions"}],"predecessor-version":[{"id":2231,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/pressbooks\/v2\/chapters\/1101\/revisions\/2231"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/pressbooks\/v2\/parts\/1066"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/pressbooks\/v2\/chapters\/1101\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/wp\/v2\/media?parent=1101"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/pressbooks\/v2\/chapter-type?post=1101"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/wp\/v2\/contributor?post=1101"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/wp\/v2\/license?post=1101"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}