{"id":1479,"date":"2017-01-24T00:41:13","date_gmt":"2017-01-24T00:41:13","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/wm-biology2\/?post_type=chapter&#038;p=1479"},"modified":"2024-04-25T18:51:56","modified_gmt":"2024-04-25T18:51:56","slug":"infections-in-humans","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/wm-biology2\/chapter\/infections-in-humans\/","title":{"raw":"Infections in Humans","rendered":"Infections in Humans"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Outcomes<\/h3>\r\n<ul>\r\n \t<li>Describe the different types of fungal infections in humans<\/li>\r\n<\/ul>\r\n<\/div>\r\n<p id=\"fs-idm113124880\">Fungi can affect animals, including humans, in several ways. A\u00a0<strong><span id=\"term936\" data-type=\"term\">mycosis<\/span><\/strong>\u00a0is a fungal disease that results from infection and direct damage due to the growth and infiltration of the fungus. Fungi attack animals directly by colonizing and destroying tissues.\u00a0<strong><span id=\"term937\" data-type=\"term\">Mycotoxicosis<\/span><\/strong>\u00a0is the poisoning of humans (and other animals) by foods contaminated by fungal toxins (mycotoxins).\u00a0<strong><span id=\"term938\" data-type=\"term\">Mycetismus<\/span><\/strong>\u00a0specifically describes the ingestion of preformed toxins in poisonous mushrooms. In addition, individuals who display hypersensitivity to molds and spores may develop strong and dangerous allergic reactions. Fungal infections are generally very difficult to treat because, unlike bacteria, fungi are eukaryotes. Antibiotics only target prokaryotic cells, whereas compounds that kill fungi also harm the eukaryotic animal host.<\/p>\r\n<p id=\"fs-idm186471888\">Many fungal infections are\u00a0<em data-effect=\"italics\">superficial<\/em>; that is, they occur on the animal\u2019s skin. Termed\u00a0<em data-effect=\"italics\">cutaneous<\/em>\u00a0(\u201cskin\u201d)\u00a0<em data-effect=\"italics\">mycoses<\/em>, they can have devastating effects. For example, the decline of the world\u2019s frog population in recent years is caused (in part) by the chytrid fungus\u00a0<em data-effect=\"italics\">Batrachochytrium dendrobatidis<\/em>. This deadly fungus infects the skin of frogs and presumably interferes with cutaneous gaseous exchange, which is essential for amphibian survival. Similarly, more than a million bats in the United States have been killed by white-nose syndrome, which appears as a white ring around the mouth of the bat. It is caused by the cold-loving fungus\u00a0<em data-effect=\"italics\">Pseudogymnoascus destructans<\/em>, which disseminates its deadly spores in caves where bats hibernate. Mycologists are researching the transmission, mechanism, and control of\u00a0<em data-effect=\"italics\">P. destructans<\/em>\u00a0to stop its spread.<\/p>\r\n<p id=\"fs-idm175923184\">Fungi that cause the superficial mycoses of the epidermis, hair, and nails rarely spread to the underlying tissue (Figure 1). These fungi are often misnamed \u201cdermatophytes\u201d, from the Greek words\u00a0<em data-effect=\"italics\">dermis<\/em>\u00a0meaning skin and<em data-effect=\"italics\">\u00a0phyte<\/em>\u00a0meaning plant, although they are not plants. Dermatophytes are also called\u00a0<em data-effect=\"italics\">\u201cringworms\u201d<\/em>\u00a0because of the red ring they cause on skin. They secrete extracellular enzymes that break down\u00a0<em data-effect=\"italics\">keratin<\/em>\u00a0(a protein found in hair, skin, and nails), causing conditions such as athlete\u2019s foot and jock itch. These conditions are usually treated with over-the-counter topical creams and powders, and are easily cleared. More persistent superficial mycoses may require prescription oral medications.<\/p>\r\n\r\n\r\n[caption id=\"attachment_1485\" align=\"aligncenter\" width=\"1024\"]<img class=\"size-large wp-image-1485\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/01\/24003952\/Figure_24_04_02abc-1024x301.jpg\" alt=\"Part A is a photo of a red, ring-shaped skin lesion. Part B is a micrograph of long, thread-like mycelia and small, oval sporangia. Part C is a chest X-ray of a person with a fungal infection.\" width=\"1024\" height=\"301\" \/> Figure 1. (a) Ringworm presents as a red ring on skin; (b) <em>Trichophyton violaceum<\/em>, shown in this bright field light micrograph, causes superficial mycoses on the scalp; (c) <em>Histoplasma capsulatum<\/em> is an ascomycete that infects airways and causes symptoms similar to influenza. (credit a: modification of work by Dr. Lucille K. Georg, CDC; credit b: modification of work by Dr. Lucille K. Georg, CDC; credit c: modification of work by M. Renz, CDC; scale-bar data from Matt Russell)[\/caption]\r\n<p id=\"fs-idm77378176\"><em data-effect=\"italics\">Systemic mycoses<\/em>\u00a0spread to internal organs, most commonly entering the body through the respiratory system. For example,\u00a0<em data-effect=\"italics\">coccidioidomycosis<\/em>\u00a0(often called valley fever) is commonly found in the southwestern United States, but as far north as Washington, where the fungus resides in the dust. Once inhaled, the spores develop in the lungs and cause symptoms similar to those of tuberculosis.\u00a0<em data-effect=\"italics\">Histoplasmosis<\/em>\u00a0is caused by the dimorphic fungus\u00a0<em data-effect=\"italics\">Histoplasma capsulatum.<\/em>\u00a0In its human host,\u00a0<em data-effect=\"italics\">Histoplasma<\/em>\u00a0grows as a yeast, causing pulmonary infections, and in rarer cases, swelling of the membranes of the brain and spinal cord. Treatment of these and many other fungal diseases requires the use of antifungal medications that have serious side effects.<\/p>\r\n<p id=\"fs-idm55827760\">Opportunistic mycoses are fungal infections that are either common in all environments, or part of the normal biota. They mainly affect individuals who have a compromised immune system. Patients in the late stages of AIDS suffer from opportunistic mycoses that can be life threatening. The yeast\u00a0<em data-effect=\"italics\">Candida<\/em>\u00a0sp., a common member of the natural biota, can grow unchecked and infect the vagina or mouth (oral thrush) if the pH of the surrounding environment, the person\u2019s immune defenses, or the normal population of bacteria are altered.<\/p>\r\n<p id=\"fs-idm142192576\"><em data-effect=\"italics\">Mycetismus<\/em>\u00a0can occur when poisonous mushrooms are eaten. It causes a number of human fatalities during mushroom-picking season. Many edible fruiting bodies of fungi resemble highly poisonous relatives, and amateur mushroom hunters are cautioned to carefully inspect their harvest and avoid eating mushrooms of doubtful origin. The adage \u201cthere are bold mushroom pickers and old mushroom pickers, but are there no old, bold mushroom pickers\u201d is unfortunately true.<\/p>\r\n\r\n<div class=\"textbox tryit\">\r\n<h3>Try It<\/h3>\r\nhttps:\/\/assess.lumenlearning.com\/practice\/9a17002e-b395-4786-9ba9-76356036160c\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Outcomes<\/h3>\n<ul>\n<li>Describe the different types of fungal infections in humans<\/li>\n<\/ul>\n<\/div>\n<p id=\"fs-idm113124880\">Fungi can affect animals, including humans, in several ways. A\u00a0<strong><span id=\"term936\" data-type=\"term\">mycosis<\/span><\/strong>\u00a0is a fungal disease that results from infection and direct damage due to the growth and infiltration of the fungus. Fungi attack animals directly by colonizing and destroying tissues.\u00a0<strong><span id=\"term937\" data-type=\"term\">Mycotoxicosis<\/span><\/strong>\u00a0is the poisoning of humans (and other animals) by foods contaminated by fungal toxins (mycotoxins).\u00a0<strong><span id=\"term938\" data-type=\"term\">Mycetismus<\/span><\/strong>\u00a0specifically describes the ingestion of preformed toxins in poisonous mushrooms. In addition, individuals who display hypersensitivity to molds and spores may develop strong and dangerous allergic reactions. Fungal infections are generally very difficult to treat because, unlike bacteria, fungi are eukaryotes. Antibiotics only target prokaryotic cells, whereas compounds that kill fungi also harm the eukaryotic animal host.<\/p>\n<p id=\"fs-idm186471888\">Many fungal infections are\u00a0<em data-effect=\"italics\">superficial<\/em>; that is, they occur on the animal\u2019s skin. Termed\u00a0<em data-effect=\"italics\">cutaneous<\/em>\u00a0(\u201cskin\u201d)\u00a0<em data-effect=\"italics\">mycoses<\/em>, they can have devastating effects. For example, the decline of the world\u2019s frog population in recent years is caused (in part) by the chytrid fungus\u00a0<em data-effect=\"italics\">Batrachochytrium dendrobatidis<\/em>. This deadly fungus infects the skin of frogs and presumably interferes with cutaneous gaseous exchange, which is essential for amphibian survival. Similarly, more than a million bats in the United States have been killed by white-nose syndrome, which appears as a white ring around the mouth of the bat. It is caused by the cold-loving fungus\u00a0<em data-effect=\"italics\">Pseudogymnoascus destructans<\/em>, which disseminates its deadly spores in caves where bats hibernate. Mycologists are researching the transmission, mechanism, and control of\u00a0<em data-effect=\"italics\">P. destructans<\/em>\u00a0to stop its spread.<\/p>\n<p id=\"fs-idm175923184\">Fungi that cause the superficial mycoses of the epidermis, hair, and nails rarely spread to the underlying tissue (Figure 1). These fungi are often misnamed \u201cdermatophytes\u201d, from the Greek words\u00a0<em data-effect=\"italics\">dermis<\/em>\u00a0meaning skin and<em data-effect=\"italics\">\u00a0phyte<\/em>\u00a0meaning plant, although they are not plants. Dermatophytes are also called\u00a0<em data-effect=\"italics\">\u201cringworms\u201d<\/em>\u00a0because of the red ring they cause on skin. They secrete extracellular enzymes that break down\u00a0<em data-effect=\"italics\">keratin<\/em>\u00a0(a protein found in hair, skin, and nails), causing conditions such as athlete\u2019s foot and jock itch. These conditions are usually treated with over-the-counter topical creams and powders, and are easily cleared. More persistent superficial mycoses may require prescription oral medications.<\/p>\n<div id=\"attachment_1485\" style=\"width: 1034px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1485\" class=\"size-large wp-image-1485\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/01\/24003952\/Figure_24_04_02abc-1024x301.jpg\" alt=\"Part A is a photo of a red, ring-shaped skin lesion. Part B is a micrograph of long, thread-like mycelia and small, oval sporangia. Part C is a chest X-ray of a person with a fungal infection.\" width=\"1024\" height=\"301\" \/><\/p>\n<p id=\"caption-attachment-1485\" class=\"wp-caption-text\">Figure 1. (a) Ringworm presents as a red ring on skin; (b) <em>Trichophyton violaceum<\/em>, shown in this bright field light micrograph, causes superficial mycoses on the scalp; (c) <em>Histoplasma capsulatum<\/em> is an ascomycete that infects airways and causes symptoms similar to influenza. (credit a: modification of work by Dr. Lucille K. Georg, CDC; credit b: modification of work by Dr. Lucille K. Georg, CDC; credit c: modification of work by M. Renz, CDC; scale-bar data from Matt Russell)<\/p>\n<\/div>\n<p id=\"fs-idm77378176\"><em data-effect=\"italics\">Systemic mycoses<\/em>\u00a0spread to internal organs, most commonly entering the body through the respiratory system. For example,\u00a0<em data-effect=\"italics\">coccidioidomycosis<\/em>\u00a0(often called valley fever) is commonly found in the southwestern United States, but as far north as Washington, where the fungus resides in the dust. Once inhaled, the spores develop in the lungs and cause symptoms similar to those of tuberculosis.\u00a0<em data-effect=\"italics\">Histoplasmosis<\/em>\u00a0is caused by the dimorphic fungus\u00a0<em data-effect=\"italics\">Histoplasma capsulatum.<\/em>\u00a0In its human host,\u00a0<em data-effect=\"italics\">Histoplasma<\/em>\u00a0grows as a yeast, causing pulmonary infections, and in rarer cases, swelling of the membranes of the brain and spinal cord. Treatment of these and many other fungal diseases requires the use of antifungal medications that have serious side effects.<\/p>\n<p id=\"fs-idm55827760\">Opportunistic mycoses are fungal infections that are either common in all environments, or part of the normal biota. They mainly affect individuals who have a compromised immune system. Patients in the late stages of AIDS suffer from opportunistic mycoses that can be life threatening. The yeast\u00a0<em data-effect=\"italics\">Candida<\/em>\u00a0sp., a common member of the natural biota, can grow unchecked and infect the vagina or mouth (oral thrush) if the pH of the surrounding environment, the person\u2019s immune defenses, or the normal population of bacteria are altered.<\/p>\n<p id=\"fs-idm142192576\"><em data-effect=\"italics\">Mycetismus<\/em>\u00a0can occur when poisonous mushrooms are eaten. It causes a number of human fatalities during mushroom-picking season. Many edible fruiting bodies of fungi resemble highly poisonous relatives, and amateur mushroom hunters are cautioned to carefully inspect their harvest and avoid eating mushrooms of doubtful origin. The adage \u201cthere are bold mushroom pickers and old mushroom pickers, but are there no old, bold mushroom pickers\u201d is unfortunately true.<\/p>\n<div class=\"textbox tryit\">\n<h3>Try It<\/h3>\n<p>\t<iframe id=\"assessment_practice_9a17002e-b395-4786-9ba9-76356036160c\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/9a17002e-b395-4786-9ba9-76356036160c?iframe_resize_id=assessment_practice_id_9a17002e-b395-4786-9ba9-76356036160c\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:300px;\"><br \/>\n\t<\/iframe>\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-1479\">\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>Biology 2e. <strong>Provided by<\/strong>: OpenStax. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8\">http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8<\/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>: Access for free at https:\/\/openstax.org\/books\/biology-2e\/pages\/1-introduction<\/li><\/ul><\/div>\n\t\t\t\t\t\t <\/div>\n\t\t\t\t\t <\/div>\n\t\t\t <\/section>","protected":false},"author":17,"menu_order":18,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"Biology 2e\",\"author\":\"\",\"organization\":\"OpenStax\",\"url\":\"http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Access for free at https:\/\/openstax.org\/books\/biology-2e\/pages\/1-introduction\"}]","CANDELA_OUTCOMES_GUID":"67273ffd-384d-4c48-a8ba-d9eb3ddf93ae, 9d33454e-383c-4607-9f74-6f581c29d733","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-1479","chapter","type-chapter","status-publish","hentry"],"part":20,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/1479","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/users\/17"}],"version-history":[{"count":8,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/1479\/revisions"}],"predecessor-version":[{"id":8347,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/1479\/revisions\/8347"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/parts\/20"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/1479\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/media?parent=1479"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapter-type?post=1479"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/contributor?post=1479"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/license?post=1479"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}