{"id":1138,"date":"2018-05-03T18:57:29","date_gmt":"2018-05-03T18:57:29","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/chapter\/fungal-parasites-and-pathogens\/"},"modified":"2018-06-13T16:00:02","modified_gmt":"2018-06-13T16:00:02","slug":"fungal-parasites-and-pathogens","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-oneonta-osbiology2e-1\/chapter\/fungal-parasites-and-pathogens\/","title":{"raw":"Fungal Parasites and Pathogens","rendered":"Fungal Parasites and Pathogens"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Objectives<\/h3>\r\nBy the end of this section, you will be able to do the following:\r\n<ul>\r\n \t<li>Describe some fungal parasites and pathogens of plants<\/li>\r\n \t<li>Describe the different types of fungal infections in humans<\/li>\r\n \t<li>Explain why antifungal therapy is hampered by the similarity between fungal and animal cells<\/li>\r\n<\/ul>\r\n<\/div>\r\n<p id=\"fs-idm68922368\">Parasitism describes a symbiotic relationship in which one member of the association benefits at the expense of the other. Both parasites and pathogens harm the host; however, pathogens cause disease, damage to host tissues or physiology, whereas parasites usually do not, but can cause serious damage and death by competition for nutrients or other resources. Commensalism occurs when one member benefits without affecting the other.<\/p>\r\n\r\n<div id=\"fs-idm66740992\" class=\"bc-section section\">\r\n<h3>Plant Parasites and Pathogens<\/h3>\r\n<p id=\"fs-idm142150304\">The production of sufficient high-quality crops is essential to human existence. Unfortunately, plant diseases have ruined many crops throughout human agricultural history, sometimes creating widespread famine. Many plant pathogens are fungi that cause tissue decay and the eventual death of the host (<a class=\"autogenerated-content\" href=\"#fig-ch24_04_01abcd\">(Figure)<\/a>). In addition to destroying plant tissue directly, some plant pathogens spoil crops by producing potent toxins that can further damage and kill the host plant. Fungi are also responsible for food spoilage and the rotting of stored crops. For example, the fungus <em>Claviceps purpurea<\/em> causes ergot, a disease of cereal crops (especially of rye). Although the fungus reduces the yield of cereals, the effects of the ergot's alkaloid toxins on humans and animals are of much greater significance. In animals, the disease is referred to as <em>ergotism<\/em>. The most common signs and symptoms are convulsions, hallucination, gangrene, and loss of milk in cattle. The active ingredient of ergot is <em>lysergic acid<\/em>, which is a precursor of the drug LSD. Smuts, rusts, and powdery or downy mildew are other examples of common fungal pathogens that affect crops.<\/p>\r\n\r\n<div id=\"fig-ch24_04_01abcd\" class=\"wp-caption aligncenter\">\r\n\r\n<span id=\"eip-idm1663712\">\r\n<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03185725\/Figure_B24_04_01abcd.png\" alt=\"Image displays various plants and fruits infected with fungal pathogens. (a) green mold on grapefruit, (b) powdery mildew covering zinnia flower and leaves, (c) red-colored rust on barley, (d) grey rot on grapes, which appears as a fibrous, almost cotton-like substance.\" width=\"408\" \/><\/span>\r\n<div class=\"wp-caption-text\">Fungal pathogens. Some fungal pathogens include (a) green mold on grapefruit, (b) powdery mildew on a zinnia, (c) stem rust on a sheaf of barley, and (d) grey rot on grapes. In wet conditions <em>Botrytis cinerea,<\/em> the fungus that causes grey rot, can destroy a grape crop. However, controlled infection of grapes by <em>Botrytis<\/em> results in noble rot, a condition that produces strong and much-prized dessert wines. (credit a: modification of work by Scott Bauer, USDA-ARS; credit b: modification of work by Stephen Ausmus, USDA-ARS; credit c: modification of work by David Marshall, USDA-ARS; credit d: modification of work by Joseph Smilanick, USDA-ARS)<\/div>\r\n<\/div>\r\n<p id=\"fs-idm129360432\">Aflatoxins are toxic, carcinogenic compounds released by fungi of the genus <em>Aspergillus<\/em>. Periodically, harvests of nuts and grains are tainted by aflatoxins, leading to massive recall of produce. This sometimes ruins producers and causes food shortages in developing countries.<\/p>\r\n\r\n<\/div>\r\n<div id=\"fs-idm139283376\" class=\"bc-section section\">\r\n<h3>Animal and Human Parasites and Pathogens<\/h3>\r\n<p id=\"fs-idm113124880\">Fungi can affect animals, including humans, in several ways. A mycosis is 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. Mycotoxicosis is the poisoning of humans (and other animals) by foods contaminated by fungal toxins (mycotoxins). Mycetismus specifically 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 <em>superficial<\/em>; that is, they occur on the animal\u2019s skin. Termed <em>cutaneous<\/em> (\u201cskin\u201d) <em>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 <em>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 <em>Pseudogymnoascus destructans<\/em>, which disseminates its deadly spores in caves where bats hibernate. Mycologists are researching the transmission, mechanism, and control of <em>P. destructans<\/em> to 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 (<a class=\"autogenerated-content\" href=\"#fig-ch24_04_02abc\">(Figure)<\/a>). These fungi are often misnamed \u201cdermatophytes\u201d, from the Greek words <em>dermis<\/em> meaning skin and<em> phyte<\/em> meaning plant, although they are not plants. Dermatophytes are also called <em>\u201cringworms\u201d<\/em> because of the red ring they cause on skin. They secrete extracellular enzymes that break down <em>keratin<\/em> (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<div id=\"fig-ch24_04_02abc\" class=\"wp-caption aligncenter\">\r\n\r\n<span id=\"fs-idm99076240\">\r\n<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03185728\/Figure_24_04_02abc.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=\"630\" \/><\/span>\r\n<div class=\"wp-caption-text\">Fungal diseases of humans. (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)<\/div>\r\n<\/div>\r\n<p id=\"fs-idm77378176\"><em>Systemic mycoses<\/em> spread to internal organs, most commonly entering the body through the respiratory system. For example, <em>coccidioidomycosis<\/em> (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. <em>Histoplasmosis<\/em> is caused by the dimorphic fungus <em>Histoplasma capsulatum.<\/em> In its human host, <em>Histoplasma<\/em> grows 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 <em>Candida<\/em> sp., 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>Mycetismus<\/em> can 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 id=\"fs-idm112408528\" class=\"scientific textbox examples\">\r\n<h3>Scientific Method Connection<\/h3>\r\n<p id=\"eip-id1168478575397\"><strong>Dutch Elm Disease<\/strong><\/p>\r\n<p id=\"fs-idm170650992\"><strong>Question<\/strong>: Do trees resistant to Dutch elm disease secrete antifungal compounds?<\/p>\r\n<p id=\"fs-idm96939104\"><strong>Hypothesis<\/strong>: Construct a hypothesis that addresses this question.<\/p>\r\n<p id=\"fs-idm186901328\"><strong>Background<\/strong>: Dutch elm disease is a fungal infestation that affects many species of elm (<em>Ulmus<\/em>) in North America. The fungus infects the vascular system of the tree, which blocks water flow within the plant and mimics drought stress. Accidently introduced to the United States in the early 1930s, it decimated American elm shade trees across the continent. It is caused by the fungus<em> Ophiostoma ulmi<\/em>. The elm bark beetle acts as a vector and transmits the disease from tree to tree. Many European and Asiatic elms are less susceptible to the disease than are American elms.<\/p>\r\n<p id=\"fs-idm178135776\"><strong>Test the hypothesis<\/strong>: A researcher testing this hypothesis might do the following. Inoculate several Petri plates containing a medium that supports the growth of fungi with fragments of <em>Ophiostoma<\/em> mycelium. Cut (with a metal punch) several disks from the vascular tissue of susceptible varieties of American elms and resistant European and Asiatic elms. Include control Petri plates inoculated with mycelia without plant tissue to verify that the medium and incubation conditions do not interfere with fungal growth. As a positive control, add paper disks impregnated with a known fungicide to Petri plates inoculated with the mycelium.<\/p>\r\n<p id=\"fs-idm126922864\">Incubate the plates for a set number of days to allow fungal growth and spreading of the mycelium over the surface of the plate. Record the diameter of the zone of clearing, if any, around the tissue samples and the fungicide control disk.<\/p>\r\n<p id=\"fs-idm120346320\">Record your observations in the following table.<\/p>\r\n\r\n<table id=\"tab-ch24_04_01\" summary=\"\">\r\n<thead>\r\n<tr>\r\n<th colspan=\"2\">Results of Antifungal Testing of Vascular Tissue from Different Species of Elm<\/th>\r\n<\/tr>\r\n<tr>\r\n<th>Disk<\/th>\r\n<th>Zone of Inhibition (mm)<\/th>\r\n<\/tr>\r\n<\/thead>\r\n<tbody>\r\n<tr>\r\n<td>Distilled Water<\/td>\r\n<td><\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Fungicide<\/td>\r\n<td><\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Tissue from Susceptible Elm #1<\/td>\r\n<td><\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Tissue from Susceptible Elm #2<\/td>\r\n<td><\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Tissue from Resistant Elm #1<\/td>\r\n<td><\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Tissue from Resistant Elm #2<\/td>\r\n<td><\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<p id=\"fs-idp18563408\">Analyze the data and report the results. Compare the effect of distilled water to the fungicide. These are negative and positive controls that validate the experimental setup. The fungicide should be surrounded by a clear zone where the fungus growth was inhibited. Is there a difference among different species of elm?<\/p>\r\n<p id=\"fs-idm68922176\"><strong>Draw a conclusion<\/strong>: Was there antifungal activity as expected from the fungicide? Did the results support the hypothesis? If not, how can this be explained? There are several possible explanations.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idm133466416\" class=\"summary textbox key-takeaways\">\r\n<h3>Section Summary<\/h3>\r\n<p id=\"fs-idm63356416\">Fungi establish parasitic relationships with plants and animals. Fungal diseases can decimate crops and spoil food during storage. Compounds produced by fungi can be toxic to humans and other animals. Mycoses are infections caused by fungi. Superficial mycoses affect the skin, whereas systemic mycoses spread through the body. Fungal infections are difficult to cure, since fungi, like their hosts, are eukaryotic, and cladistically related closely to Kingdom Animalia.<\/p>\r\n\r\n<\/div>\r\n<div id=\"fs-idm167376928\" class=\"multiple-choice textbox exercises\">\r\n<h3>Review Questions<\/h3>\r\n<div id=\"fs-idm33048112\">\r\n<div id=\"fs-idm76368880\">\r\n<p id=\"fs-idm163649360\">A fungus that climbs up a tree reaching higher elevation to release its spores in the wind and does not receive any nutrients from the tree or contribute to the tree\u2019s welfare is described as a ________.<\/p>\r\n\r\n<ol id=\"fs-idm161698848\" type=\"a\">\r\n \t<li>commensal<\/li>\r\n \t<li>mutualist<\/li>\r\n \t<li>parasite<\/li>\r\n \t<li>pathogen<\/li>\r\n<\/ol>\r\n<\/div>\r\n[reveal-answer q=\"fs-idm181769472\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-idm181769472\"]\r\n<div id=\"fs-idm181769472\">\r\n<p id=\"fs-idm82760880\">A<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"fs-idp5013264\">\r\n<div id=\"fs-idm118332720\">\r\n<p id=\"fs-idm32192832\">A fungal infection that affects nails and skin is classified as ________.<\/p>\r\n\r\n<ol id=\"fs-idm190333760\" type=\"a\">\r\n \t<li>systemic mycosis<\/li>\r\n \t<li>mycetismus<\/li>\r\n \t<li>superficial mycosis<\/li>\r\n \t<li>mycotoxicosis<\/li>\r\n<\/ol>\r\n<\/div>\r\n[reveal-answer q=\"fs-idm191703728\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-idm191703728\"]\r\n<div id=\"fs-idm191703728\">\r\n<p id=\"fs-idm68621344\">C<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"eip-554\">\r\n<div id=\"eip-760\">\r\n<p id=\"eip-605\">The targets for anti-fungal drugs are much more limited than antibiotics or anti-viral medications. Why?<\/p>\r\n\r\n<ol id=\"list-idp009\" type=\"a\">\r\n \t<li>There are more bacteria and viruses than fungi.<\/li>\r\n \t<li>Fungi can only be targeted during sexual reproduction, while bacteria and viruses can be targeted at any point in their lifespan.<\/li>\r\n \t<li>Fungi cause topical infections, while viruses and bacteria cause systemic infections.<\/li>\r\n \t<li>Human cells are much more similar to fungi cells than bacteria or viruses.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<div id=\"eip-367\">\r\n<p id=\"eip-286\">\r\n[reveal-answer q=\"749974\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"749974\"]<\/p>\r\nD[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idm164988816\" class=\"free-response textbox exercises\">\r\n<h3>Free Response<\/h3>\r\n<div id=\"fs-idm148472896\">\r\n<div id=\"fs-idm186455360\">\r\n<p id=\"fs-idm176233552\">Why can superficial mycoses in humans lead to bacterial infections?<\/p>\r\n\r\n<\/div>\r\n[reveal-answer q=\"fs-idm98833760\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-idm98833760\"]\r\n<div id=\"fs-idm98833760\">\r\n<p id=\"fs-idm112177392\">Dermatophytes that colonize skin break down the keratinized layer of dead cells that protects tissues from bacterial invasion. Once the integrity of the skin is breached, bacteria can enter the deeper layers of tissues and cause infections.<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"eip-398\">\r\n<div id=\"eip-167\">\r\n<p id=\"eip-764\">Explain how the Red Queen Hypothesis describes the continuously evolving relationship between red grapes and <em>Botrytis cinerea<\/em>.<\/p>\r\n\r\n<\/div>\r\n<div id=\"eip-386\">\r\n<p id=\"eip-624\">\r\n[reveal-answer q=\"126939\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"126939\"]<\/p>\r\nThe Red Queen Hypothesis describes the biological stalemate between a predator and prey. The two populations are constantly applying evolutionary pressure on each other, forcing each population to adapt to counter an adaptation of the other population. In the case of the fungi B. cinerea and the red grape plant, the grapes are the prey and the fungi are the predator in the Red Queen Hypothesis. The grapes develop defenses to prevent infection by the fungi, ensuring that the B. cinerea that survive to colonize the red grapes have developed adaptations to overcome the plant defenses. The red grapes that then survive the infection are the plants that have additional adaptations that limit the pathogenicity of B. cinerea. This cycle continues to repeat unless one population evolves an adaptation that cannot be countered by the other population, which would wipe out the later population.[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"textbox shaded\">\r\n<h3>Glossary<\/h3>\r\n<dl id=\"fs-idm128042480\">\r\n \t<dt>commensalism<\/dt>\r\n \t<dd id=\"fs-idm164343840\">symbiotic relationship in which one member benefits while the other member is not affected<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idm186127504\">\r\n \t<dt>mycetismus<\/dt>\r\n \t<dd id=\"fs-idm122192016\">ingestion of toxins in poisonous mushrooms<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idm139193440\">\r\n \t<dt>mycosis<\/dt>\r\n \t<dd id=\"fs-idm127346304\">fungal infection<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idm186145456\">\r\n \t<dt>mycotoxicosis<\/dt>\r\n \t<dd id=\"fs-idm114974896\">poisoning by a fungal toxin released in food<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idm77715248\">\r\n \t<dt>parasitism<\/dt>\r\n \t<dd id=\"fs-idm201066800\">symbiotic relationship in which one member of the association benefits at the expense of the other<\/dd>\r\n<\/dl>\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Objectives<\/h3>\n<p>By the end of this section, you will be able to do the following:<\/p>\n<ul>\n<li>Describe some fungal parasites and pathogens of plants<\/li>\n<li>Describe the different types of fungal infections in humans<\/li>\n<li>Explain why antifungal therapy is hampered by the similarity between fungal and animal cells<\/li>\n<\/ul>\n<\/div>\n<p id=\"fs-idm68922368\">Parasitism describes a symbiotic relationship in which one member of the association benefits at the expense of the other. Both parasites and pathogens harm the host; however, pathogens cause disease, damage to host tissues or physiology, whereas parasites usually do not, but can cause serious damage and death by competition for nutrients or other resources. Commensalism occurs when one member benefits without affecting the other.<\/p>\n<div id=\"fs-idm66740992\" class=\"bc-section section\">\n<h3>Plant Parasites and Pathogens<\/h3>\n<p id=\"fs-idm142150304\">The production of sufficient high-quality crops is essential to human existence. Unfortunately, plant diseases have ruined many crops throughout human agricultural history, sometimes creating widespread famine. Many plant pathogens are fungi that cause tissue decay and the eventual death of the host (<a class=\"autogenerated-content\" href=\"#fig-ch24_04_01abcd\">(Figure)<\/a>). In addition to destroying plant tissue directly, some plant pathogens spoil crops by producing potent toxins that can further damage and kill the host plant. Fungi are also responsible for food spoilage and the rotting of stored crops. For example, the fungus <em>Claviceps purpurea<\/em> causes ergot, a disease of cereal crops (especially of rye). Although the fungus reduces the yield of cereals, the effects of the ergot&#8217;s alkaloid toxins on humans and animals are of much greater significance. In animals, the disease is referred to as <em>ergotism<\/em>. The most common signs and symptoms are convulsions, hallucination, gangrene, and loss of milk in cattle. The active ingredient of ergot is <em>lysergic acid<\/em>, which is a precursor of the drug LSD. Smuts, rusts, and powdery or downy mildew are other examples of common fungal pathogens that affect crops.<\/p>\n<div id=\"fig-ch24_04_01abcd\" class=\"wp-caption aligncenter\">\n<p><span id=\"eip-idm1663712\"><br \/>\n<img decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03185725\/Figure_B24_04_01abcd.png\" alt=\"Image displays various plants and fruits infected with fungal pathogens. (a) green mold on grapefruit, (b) powdery mildew covering zinnia flower and leaves, (c) red-colored rust on barley, (d) grey rot on grapes, which appears as a fibrous, almost cotton-like substance.\" width=\"408\" \/><\/span><\/p>\n<div class=\"wp-caption-text\">Fungal pathogens. Some fungal pathogens include (a) green mold on grapefruit, (b) powdery mildew on a zinnia, (c) stem rust on a sheaf of barley, and (d) grey rot on grapes. In wet conditions <em>Botrytis cinerea,<\/em> the fungus that causes grey rot, can destroy a grape crop. However, controlled infection of grapes by <em>Botrytis<\/em> results in noble rot, a condition that produces strong and much-prized dessert wines. (credit a: modification of work by Scott Bauer, USDA-ARS; credit b: modification of work by Stephen Ausmus, USDA-ARS; credit c: modification of work by David Marshall, USDA-ARS; credit d: modification of work by Joseph Smilanick, USDA-ARS)<\/div>\n<\/div>\n<p id=\"fs-idm129360432\">Aflatoxins are toxic, carcinogenic compounds released by fungi of the genus <em>Aspergillus<\/em>. Periodically, harvests of nuts and grains are tainted by aflatoxins, leading to massive recall of produce. This sometimes ruins producers and causes food shortages in developing countries.<\/p>\n<\/div>\n<div id=\"fs-idm139283376\" class=\"bc-section section\">\n<h3>Animal and Human Parasites and Pathogens<\/h3>\n<p id=\"fs-idm113124880\">Fungi can affect animals, including humans, in several ways. A mycosis is 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. Mycotoxicosis is the poisoning of humans (and other animals) by foods contaminated by fungal toxins (mycotoxins). Mycetismus specifically 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 <em>superficial<\/em>; that is, they occur on the animal\u2019s skin. Termed <em>cutaneous<\/em> (\u201cskin\u201d) <em>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 <em>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 <em>Pseudogymnoascus destructans<\/em>, which disseminates its deadly spores in caves where bats hibernate. Mycologists are researching the transmission, mechanism, and control of <em>P. destructans<\/em> to 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 (<a class=\"autogenerated-content\" href=\"#fig-ch24_04_02abc\">(Figure)<\/a>). These fungi are often misnamed \u201cdermatophytes\u201d, from the Greek words <em>dermis<\/em> meaning skin and<em> phyte<\/em> meaning plant, although they are not plants. Dermatophytes are also called <em>\u201cringworms\u201d<\/em> because of the red ring they cause on skin. They secrete extracellular enzymes that break down <em>keratin<\/em> (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=\"fig-ch24_04_02abc\" class=\"wp-caption aligncenter\">\n<p><span id=\"fs-idm99076240\"><br \/>\n<img decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03185728\/Figure_24_04_02abc.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=\"630\" \/><\/span><\/p>\n<div class=\"wp-caption-text\">Fungal diseases of humans. (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)<\/div>\n<\/div>\n<p id=\"fs-idm77378176\"><em>Systemic mycoses<\/em> spread to internal organs, most commonly entering the body through the respiratory system. For example, <em>coccidioidomycosis<\/em> (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. <em>Histoplasmosis<\/em> is caused by the dimorphic fungus <em>Histoplasma capsulatum.<\/em> In its human host, <em>Histoplasma<\/em> grows 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 <em>Candida<\/em> sp., 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>Mycetismus<\/em> can 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 id=\"fs-idm112408528\" class=\"scientific textbox examples\">\n<h3>Scientific Method Connection<\/h3>\n<p id=\"eip-id1168478575397\"><strong>Dutch Elm Disease<\/strong><\/p>\n<p id=\"fs-idm170650992\"><strong>Question<\/strong>: Do trees resistant to Dutch elm disease secrete antifungal compounds?<\/p>\n<p id=\"fs-idm96939104\"><strong>Hypothesis<\/strong>: Construct a hypothesis that addresses this question.<\/p>\n<p id=\"fs-idm186901328\"><strong>Background<\/strong>: Dutch elm disease is a fungal infestation that affects many species of elm (<em>Ulmus<\/em>) in North America. The fungus infects the vascular system of the tree, which blocks water flow within the plant and mimics drought stress. Accidently introduced to the United States in the early 1930s, it decimated American elm shade trees across the continent. It is caused by the fungus<em> Ophiostoma ulmi<\/em>. The elm bark beetle acts as a vector and transmits the disease from tree to tree. Many European and Asiatic elms are less susceptible to the disease than are American elms.<\/p>\n<p id=\"fs-idm178135776\"><strong>Test the hypothesis<\/strong>: A researcher testing this hypothesis might do the following. Inoculate several Petri plates containing a medium that supports the growth of fungi with fragments of <em>Ophiostoma<\/em> mycelium. Cut (with a metal punch) several disks from the vascular tissue of susceptible varieties of American elms and resistant European and Asiatic elms. Include control Petri plates inoculated with mycelia without plant tissue to verify that the medium and incubation conditions do not interfere with fungal growth. As a positive control, add paper disks impregnated with a known fungicide to Petri plates inoculated with the mycelium.<\/p>\n<p id=\"fs-idm126922864\">Incubate the plates for a set number of days to allow fungal growth and spreading of the mycelium over the surface of the plate. Record the diameter of the zone of clearing, if any, around the tissue samples and the fungicide control disk.<\/p>\n<p id=\"fs-idm120346320\">Record your observations in the following table.<\/p>\n<table id=\"tab-ch24_04_01\" summary=\"\">\n<thead>\n<tr>\n<th colspan=\"2\">Results of Antifungal Testing of Vascular Tissue from Different Species of Elm<\/th>\n<\/tr>\n<tr>\n<th>Disk<\/th>\n<th>Zone of Inhibition (mm)<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Distilled Water<\/td>\n<td><\/td>\n<\/tr>\n<tr>\n<td>Fungicide<\/td>\n<td><\/td>\n<\/tr>\n<tr>\n<td>Tissue from Susceptible Elm #1<\/td>\n<td><\/td>\n<\/tr>\n<tr>\n<td>Tissue from Susceptible Elm #2<\/td>\n<td><\/td>\n<\/tr>\n<tr>\n<td>Tissue from Resistant Elm #1<\/td>\n<td><\/td>\n<\/tr>\n<tr>\n<td>Tissue from Resistant Elm #2<\/td>\n<td><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p id=\"fs-idp18563408\">Analyze the data and report the results. Compare the effect of distilled water to the fungicide. These are negative and positive controls that validate the experimental setup. The fungicide should be surrounded by a clear zone where the fungus growth was inhibited. Is there a difference among different species of elm?<\/p>\n<p id=\"fs-idm68922176\"><strong>Draw a conclusion<\/strong>: Was there antifungal activity as expected from the fungicide? Did the results support the hypothesis? If not, how can this be explained? There are several possible explanations.<\/p>\n<\/div>\n<\/div>\n<div id=\"fs-idm133466416\" class=\"summary textbox key-takeaways\">\n<h3>Section Summary<\/h3>\n<p id=\"fs-idm63356416\">Fungi establish parasitic relationships with plants and animals. Fungal diseases can decimate crops and spoil food during storage. Compounds produced by fungi can be toxic to humans and other animals. Mycoses are infections caused by fungi. Superficial mycoses affect the skin, whereas systemic mycoses spread through the body. Fungal infections are difficult to cure, since fungi, like their hosts, are eukaryotic, and cladistically related closely to Kingdom Animalia.<\/p>\n<\/div>\n<div id=\"fs-idm167376928\" class=\"multiple-choice textbox exercises\">\n<h3>Review Questions<\/h3>\n<div id=\"fs-idm33048112\">\n<div id=\"fs-idm76368880\">\n<p id=\"fs-idm163649360\">A fungus that climbs up a tree reaching higher elevation to release its spores in the wind and does not receive any nutrients from the tree or contribute to the tree\u2019s welfare is described as a ________.<\/p>\n<ol id=\"fs-idm161698848\" type=\"a\">\n<li>commensal<\/li>\n<li>mutualist<\/li>\n<li>parasite<\/li>\n<li>pathogen<\/li>\n<\/ol>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-idm181769472\">Show Solution<\/span><\/p>\n<div id=\"qfs-idm181769472\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-idm181769472\">\n<p id=\"fs-idm82760880\">A<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idp5013264\">\n<div id=\"fs-idm118332720\">\n<p id=\"fs-idm32192832\">A fungal infection that affects nails and skin is classified as ________.<\/p>\n<ol id=\"fs-idm190333760\" type=\"a\">\n<li>systemic mycosis<\/li>\n<li>mycetismus<\/li>\n<li>superficial mycosis<\/li>\n<li>mycotoxicosis<\/li>\n<\/ol>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-idm191703728\">Show Solution<\/span><\/p>\n<div id=\"qfs-idm191703728\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-idm191703728\">\n<p id=\"fs-idm68621344\">C<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"eip-554\">\n<div id=\"eip-760\">\n<p id=\"eip-605\">The targets for anti-fungal drugs are much more limited than antibiotics or anti-viral medications. Why?<\/p>\n<ol id=\"list-idp009\" type=\"a\">\n<li>There are more bacteria and viruses than fungi.<\/li>\n<li>Fungi can only be targeted during sexual reproduction, while bacteria and viruses can be targeted at any point in their lifespan.<\/li>\n<li>Fungi cause topical infections, while viruses and bacteria cause systemic infections.<\/li>\n<li>Human cells are much more similar to fungi cells than bacteria or viruses.<\/li>\n<\/ol>\n<\/div>\n<div id=\"eip-367\">\n<p id=\"eip-286\">\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q749974\">Show Solution<\/span><\/p>\n<div id=\"q749974\" class=\"hidden-answer\" style=\"display: none\">\n<p>D<\/p><\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idm164988816\" class=\"free-response textbox exercises\">\n<h3>Free Response<\/h3>\n<div id=\"fs-idm148472896\">\n<div id=\"fs-idm186455360\">\n<p id=\"fs-idm176233552\">Why can superficial mycoses in humans lead to bacterial infections?<\/p>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-idm98833760\">Show Solution<\/span><\/p>\n<div id=\"qfs-idm98833760\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-idm98833760\">\n<p id=\"fs-idm112177392\">Dermatophytes that colonize skin break down the keratinized layer of dead cells that protects tissues from bacterial invasion. Once the integrity of the skin is breached, bacteria can enter the deeper layers of tissues and cause infections.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"eip-398\">\n<div id=\"eip-167\">\n<p id=\"eip-764\">Explain how the Red Queen Hypothesis describes the continuously evolving relationship between red grapes and <em>Botrytis cinerea<\/em>.<\/p>\n<\/div>\n<div id=\"eip-386\">\n<p id=\"eip-624\">\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q126939\">Show Solution<\/span><\/p>\n<div id=\"q126939\" class=\"hidden-answer\" style=\"display: none\">\n<p>The Red Queen Hypothesis describes the biological stalemate between a predator and prey. The two populations are constantly applying evolutionary pressure on each other, forcing each population to adapt to counter an adaptation of the other population. In the case of the fungi B. cinerea and the red grape plant, the grapes are the prey and the fungi are the predator in the Red Queen Hypothesis. The grapes develop defenses to prevent infection by the fungi, ensuring that the B. cinerea that survive to colonize the red grapes have developed adaptations to overcome the plant defenses. The red grapes that then survive the infection are the plants that have additional adaptations that limit the pathogenicity of B. cinerea. This cycle continues to repeat unless one population evolves an adaptation that cannot be countered by the other population, which would wipe out the later population.<\/p><\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox shaded\">\n<h3>Glossary<\/h3>\n<dl id=\"fs-idm128042480\">\n<dt>commensalism<\/dt>\n<dd id=\"fs-idm164343840\">symbiotic relationship in which one member benefits while the other member is not affected<\/dd>\n<\/dl>\n<dl id=\"fs-idm186127504\">\n<dt>mycetismus<\/dt>\n<dd id=\"fs-idm122192016\">ingestion of toxins in poisonous mushrooms<\/dd>\n<\/dl>\n<dl id=\"fs-idm139193440\">\n<dt>mycosis<\/dt>\n<dd id=\"fs-idm127346304\">fungal infection<\/dd>\n<\/dl>\n<dl id=\"fs-idm186145456\">\n<dt>mycotoxicosis<\/dt>\n<dd id=\"fs-idm114974896\">poisoning by a fungal toxin released in food<\/dd>\n<\/dl>\n<dl id=\"fs-idm77715248\">\n<dt>parasitism<\/dt>\n<dd id=\"fs-idm201066800\">symbiotic relationship in which one member of the association benefits at the expense of the other<\/dd>\n<\/dl>\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-1138\">\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=\"https:\/\/openstax.org\/details\/books\/biology-2e\">https:\/\/openstax.org\/details\/books\/biology-2e<\/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\/8d50a0af-948b-4204-a71d-4826cba765b8@8.19<\/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":311,"menu_order":5,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"Biology 2e\",\"author\":\"\",\"organization\":\"OpenStax\",\"url\":\"https:\/\/openstax.org\/details\/books\/biology-2e\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Download for free at http:\/\/cnx.org\/contents\/8d50a0af-948b-4204-a71d-4826cba765b8@8.19\"}]","CANDELA_OUTCOMES_GUID":"","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-1138","chapter","type-chapter","status-publish","hentry"],"part":1106,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/suny-oneonta-osbiology2e-1\/wp-json\/pressbooks\/v2\/chapters\/1138","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/suny-oneonta-osbiology2e-1\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/suny-oneonta-osbiology2e-1\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-oneonta-osbiology2e-1\/wp-json\/wp\/v2\/users\/311"}],"version-history":[{"count":1,"href":"https:\/\/courses.lumenlearning.com\/suny-oneonta-osbiology2e-1\/wp-json\/pressbooks\/v2\/chapters\/1138\/revisions"}],"predecessor-version":[{"id":2201,"href":"https:\/\/courses.lumenlearning.com\/suny-oneonta-osbiology2e-1\/wp-json\/pressbooks\/v2\/chapters\/1138\/revisions\/2201"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/suny-oneonta-osbiology2e-1\/wp-json\/pressbooks\/v2\/parts\/1106"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/suny-oneonta-osbiology2e-1\/wp-json\/pressbooks\/v2\/chapters\/1138\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/suny-oneonta-osbiology2e-1\/wp-json\/wp\/v2\/media?parent=1138"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-oneonta-osbiology2e-1\/wp-json\/pressbooks\/v2\/chapter-type?post=1138"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-oneonta-osbiology2e-1\/wp-json\/wp\/v2\/contributor?post=1138"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-oneonta-osbiology2e-1\/wp-json\/wp\/v2\/license?post=1138"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}