Animal diseases caused by microscopic fungi. Diseases caused by fungi Diseases associated with fungi
Some species of fungi can be pathogenic for warm-blooded animals and humans and cause them suffering. Mycoses that affect the internal organs of humans and animals are often infectious. The following mycoses are known: pulmonary pseudotuberculosis, intestinal mycoses, otomycosis (purulent inflammation of the ear), mycoses that cause inflammation of the nasal cavity and eyes. The most common are mycoses of the external integument of humans and animals (dermatomycosis). Among them, diseases such as scab, ringworm (trichophytia), epidermophytosis, microsporia, etc. are known. Sometimes diseases of animals and humans cause mycotoxicosis: plants infected by fungi produce toxins that enter the body of animals or humans in various ways and lead to to poisoning and even death. Mycotoxicosis is caused by ergot of bread and fodder cereals, as well as “drunk” bread made from grain contaminated with fungi of the genus Fusarium. The toxic effect is caused by corn smut.
Mycoses
Mycoses of animals and humans are distributed almost throughout the globe. The manifestation of mycotic diseases in humans and animals is facilitated by a number of factors, such as, for example, contact with sick animals and humans, trauma, poor skin and hair care. Human infection is possible through the respiratory tract and by ingesting food. Some actinomycetes, yeasts and yeast-like fungi cause damage to the gastrointestinal tract, and Aspergillus species cause pseudotuberculosis in animals and humans. Once embedded in the tissue, they can develop there for decades. Dermatophytes remain viable in hairs and skin scales for a very long time (6-7 years). Mushrooms die at high temperatures (at 80°C after 5-7 minutes). Sublimate, salicylic and benzoic acids, formalin are characterized by fungidid properties. Ultraviolet rays and rays of a mercury-quartz lamp kill mushrooms. Dermatomycosis is widespread.
Ringworm, or trichophytosis
This common disease is caused by fungi of the genus Trichophyton. Trichophytosis affects the skin, hair, and less often internal organs. The disease is active in children; in adults it takes a chronic, atypical form. Typically, patches of baldness with flaky skin appear on the scalp. Whitish-grayish hair stumps 2-4 mm high protrude above the surface of the skin. The affected hair is filled with fungal spores. In the purulent form of the disease, pustules are formed that are squeezed out through the hair follicles. During the illness, which lasts 2-3 months, the body is in a depressed state. The infected person has severe headaches, the temperature rises to 38-39°. During recovery, scars form, preventing further hair growth. In addition to hair, smooth skin and nails are affected. The skin becomes covered with blisters, which dry out and form a yellowish crust. This form of the disease is more common in women. Affected fingernails and toenails change color, shape, consistency and become uneven, loose and crumbling.
Microsporia
The disease is caused by fungi of the genus Microsporium and is observed in children under 13-15 years of age. There are species that live only on humans, others live only on animals, and the species Microsporium lanosum affects humans and animals. Microsporia is transmitted to humans by cats and dogs. Microsporia affects hairy and smooth skin, less often nails. This disease resembles trichophytosis, only the hair stumps are longer. In areas of baldness and in nails, the fungus is found in the form of hyphae. In adults, predominantly smooth skin is affected. In this case, bubbles are formed, located in concentric circles on the reddened spot. The bubbles then dry out and crusts appear in their place.
Scab
The disease is caused by mushrooms of the genus Achorion. Hair, nails, smooth skin, and less commonly internal organs are affected. The disease lasts for years and is often fatal. Achorion species are specialized in relation to humans and animals. With this disease, saucer-shaped yellow, rather dense scutes (scutules) appear on the head, smooth skin and nails. The scutulae are difficult to separate from the lesions, exposing the ulcerative surface. The hair becomes sparse, whitish, dry and falls out entirely. The baldness observed with the disease is very persistent. The cervical lymph nodes enlarge, and sometimes contain the causative agent of the disease inside them. Blisters form on smooth skin. Nails are affected in the same way as with trichophytosis. When internal organs, bones and the central nervous system are damaged, the patient experiences exhaustion, fever, intoxication - all this often leads to death.
Thrush
The disease occurs in humans, domestic animals and birds. A person becomes susceptible to disease when immunity decreases. Infants are most often affected. The causative agent of the disease is the fungus oidium albicans (candida). The fungus's habitat is the oral cavity, where it forms white plaques resembling milk curds. Plaques grow to the mucous membrane, and ulcers with small hemorrhages appear under them. Adults who are weakened by diabetes, cancer or tuberculosis are especially susceptible to thrush. In severe cases, the fungus spreads to the esophagus, stomach and respiratory tract, making swallowing and breathing difficult. The spread of this disease can cause inflammation of the lungs, middle ear and even skin.
Pseudotuberculosis
The causative agent of the disease is the fungus Aspergillus fumigatus. The disease is common mainly among chickens and turkeys. Warm-blooded animals and humans also get sick. Pseudotuberculosis in humans is very similar in the course of the disease to pulmonary tuberculosis: cough with sputum, bleeding and fever. The disease lasts for years and is difficult to treat. Aspergillus fumigatus also causes inflammation in the ears (otomycosis), accompanied by noise, itching and pain, and sometimes dizziness and cough. Mycelial plugs sometimes form in the ears. As a result of the disease, partial or complete hearing loss is observed.
Mycotoxicoses
Ergot in grain, fodder and wild cereals is toxic to animals and humans. Ergot sclerotia are used as a medicine to treat hypertension, mental and other diseases. Small mature ergot sclerotia (horns) are especially poisonous and lose toxicity after 9-12 months. Ergot poisoning causes prolonged cramps in the legs and arms - “evil writhing.” Patients feel general malaise and weakness. Saliva is released from the mouth, vomiting, diarrhea and stomach pain appear. The temperature often rises. There are cases of epilepsy and mental neurosis. Sometimes a gangrenous form of the disease (death of the limbs) is observed. Ergot gets into the grain, and when grinding, into the flour. The more cones that get into the flour, the more toxic it is. Ergot contains various alkaloids that are toxic to humans. It is toxic to cattle, horses, sheep, pigs, dogs, cats, and birds. When poisoned, animals experience general depression, weak pulse and breathing, decreased sensitivity, then general muscle paralysis occurs - the animal lies down and slowly dies. In the Leningrad region, currently, as a rule, measures to combat ergot are observed, so toxicosis has not been registered.
Animal stachybotriotoxicosis
The development of a large number of molds on straw causes disease in animals, but straw infected with the fungus Stachybotrys alternans is especially toxic. This fungus, developing saprotrophically on stubble, straw, dried stems of many plants, manure, paper, shavings, wood, decomposes fiber and releases toxic substances into the substrate. When horses eat poisonous feed, they experience irritation of the mucous membranes of the mouth and intestines, and then ulceration of the stomach. The toxin persists in affected straw for 12 years. Cows are almost insensitive to this toxin; cats, on the contrary, show all the symptoms of this disease. The mushroom tolerates low temperatures well; It develops strongly in the presence of moisture, but quickly dies from elevated temperatures. Currently, this disease almost never occurs.
The causative agents of superficial mycoses include several pathogenic fungi.
Epidermophyton , calling epi dermophytosis nails, feet, groin area. The disease is clinically manifested by the formation of various inflammatory rashes on the corresponding areas of the skin - vesicles, blisters and erosions, as well as deformation and subsequent destruction of the nails.
Pathogenic molds of the genusMicrosporum , causing various microsporia , - diseases affecting the stratum corneum of the skin and hair; clinically manifested by the appearance of irregularly shaped lesions on the scalp; the hair in the lesions is broken off at a height of 6 - 8 mm above the skin level and is covered with a pale gray sheath consisting of fungal spores. On smooth skin, multiple lesions form in the form of regular rings, limited by an inflammatory ridge.
Pathogenic molds of the genusTrichophyton , calling tricho fitia (syn.: ringworm), which, depending on the type of pathogen, clinically manifests itself as both a superficial and an infiltration-suppurative form of the disease. Superficial dermatomycosis caused by these fungi includes favus(from lat. favus - cellular cell; synonym: scab) is a skin and hair disease caused by Trichophyton schoenleinii and characterized by the formation of scutulae and cicatricial atrophy of the skin. The scutula, or scutum, is a yellow-gray crust with raised edges, resembling a saucer. A peculiar “mouse” (barn) smell emanates from the scutuli. After the scutulae fall off, foci of skin atrophy form in their place. Besides Trichophyton schoenleinii superficial trichophytosis is caused by lamellar fungi Trichophyton violaceum And Trichophyton tonsurans, which affect the stratum corneum of the epidermis and hair. A characteristic clinical manifestation of superficial trichophytosis is dark skin flakes - “black dots”, localized at the site of hair follicles affected by the fungus.
Infiltrative-suppurative trichophytosis caused by molds Trichophyton verrucosum And Trichophyton mentagrophytes. This dermatomycosis characterized by inflammatory skin lesions and subsequent formation of deep follicular abscesses.
Pathogenic yeast fungus of the genusCandida causes surface candidiasis skin and mucous membranes. The clinical picture of the disease is varied - the appearance of cracks on the skin, weeping red-white erosions, red wet erosion in the corners of the mouth - candidomycotic infection, yeast stomatitis, yeast vulvovaginitis, etc.
To pathogens of deep or systemic mycoses include pathogenic fungi that cause the following diseases.
Histoplasmosis (syn.: Darling disease), cause pathogenic dimoRussian mushroomsHistoplasma capsulatum (fungi that combine the morphological characteristics of mold and yeast-like fungi) . The disease is characterized by hyperplasia (increase in mass) of lung tissue, the development of cardiopulmonary failure, hepatic-splenic-lymphatic syndrome and/or skin-mucosal-ulcerative syndrome.
Disseminated candidiasis caused by yeastsCandida albicans . The disease is characterized by the formation of small necrotic foci in the internal organs (lungs, heart, brain, kidneys).
Sporotrichosis (syn.: Schenk-Berman disease) cause pathogenic dimorphic fungiSporothrix schenckii . The clinical picture of the disease is characterized by the formation of ulcerated nodes along the lymphatic vessels, less often by damage to muscles, bones, and internal organs.
Chromomycosis (syn.: chromoblastomycosis, Pedroso disease) cause pathogenic molds of the genusPhialophora . The clinical picture of the disease is characterized mainly by damage to the skin, subcutaneous tissue, bones, as well as the formation of nodules in internal organs, including brain tissue, in which ulcerated nodules and microabscesses form.
Besides to systemic mycoses relate blastomycosis (causative agent - pathogenic dimorphic fungi of the genus Blastomyces dermatitidis), coccidioidomycosis(pathogen pathogenic dimorphic fungi Coccidioides immitis), cryptococcosis(causative agent - pathogenic yeast-like fungi Cryptococcus neoformans) and other diseases characterized by damage to various parenchymal organs and tissues.
Diseases caused by fungi are divided, depending on their cause, into two large groups:
* mycoses, or fungal diseases that develop as a result of direct parasitism of fungi in the human or animal body - on the skin (dermatomycosis) or in internal organs (so-called deep mycoses);
* mycotoxicosis, or mushroom poisoning associated with the formation of poisons (toxins) by mushrooms; Such poisoning is caused by eating food or feed on which toxic fungi have developed. Among the diseases that can be caused by fungi or their metabolic products, various allergic reactions should be mentioned. They are caused in some people by inhaling airborne fungal spores or by eating completely edible mushrooms, such as autumn mushrooms. Some pathogenic and numerous saprotrophic fungi, whose spores are constantly in the air and dust, have allergenic properties. More than 300 species of fungi are known to cause allergic reactions. Among them are such widespread inhabitants of the soil and various plant debris as penicillium, aspergillus, alternaria, cladosporium, etc. Inhalation of spores of such fungi causes bronchial asthma, allergic rhinitis, and hay fever in a person with hypersensitivity to them. There are known cases where allergic reactions were caused by spores of some macromycetes formed in mass quantities, for example house fungus, large discomycetes, etc. Doctors often encounter in their practice allergic reactions to various metabolic products of fungi, such as antibiotics and toxins. Some patients are hypersensitive to penicillins, and they cause various forms of allergies - from itchy skin and rashes to deadly anaphylactic shock. People vary greatly both in their tendency to sensitize (increase sensitivity) to allergens and in the types of allergic reactions, so they are not observed in everyone who encounters allergens.
Mycoses. Of the huge number of fungal species, only relatively few (about 2000) are capable of parasitizing animal organisms and the human body. However, among them there are causative agents of quite common and sometimes life-threatening diseases.
One of the most common groups of such fungi is dermatophytes, which live on the skin and cause diseases (dermatomycosis) in humans and many animals. Such fungi form enzymes that destroy keratin, a very strong protein that is part of hair and other skin formations, and are resistant to skin secretions. Many dermatomycoses, such as scab, have been known since ancient times.
Dermatophyte fungi are adapted to parasitism to varying degrees and have different host ranges. The most specialized of them cause diseases only in humans and do not infect animals. When they get into the soil, such mushrooms quickly die. Very common and dangerous are less specialized species that can infect both humans and animals, and the infection is often transmitted from domestic animals to humans. An example of this is the causative agent of microsporia in dogs and cats. Fungi of this group parasitize not only domestic animals, but also some wild animals - voles, mice, shrews, etc., which can also be a source of infection with dermatomycosis. Some less specialized dermatophytes can live or persist in the soil for a long time, which also increases the risk of infection by them.
In addition to dermatomycosis, fungi can affect various internal organs, causing a number of diseases - histoplasmosis, cryptococcosis, candidiasis, etc. The causative agent of histoplasmosis - histoplasma capsularis is found in the cells of the bone marrow, spleen, liver, lungs and other organs. This disease is known in many countries, but develops in separate local foci in certain areas of the globe, mainly with a mild climate - in these areas histoplasma is isolated from soil and water. Histoplasma is especially common in the excrement of bats and birds, which are carriers of this dangerous disease. The literature describes cases of histoplasmosis among groups of speleologists who visited caves inhabited by bats.
The causative agents of diseases in humans and warm-blooded animals can also be some widespread saprotrophic fungi that usually live in the soil and on various organic substrates, for example Aspergillus fume. It often causes damage to the respiratory tract in birds, and in humans - otomycosis, aspergillosis and emphysema. The spores of this fungus and the toxin it produces can cause allergic reactions with symptoms of sore throat.
Mycotoxicoses. In recent years, toxicologists have been paying more and more attention to microscopic fungi that, developing on plants, food or feed, produce toxins that cause poisoning when such products or feed are consumed.
One of the most common and long-known toxic fungi is ergot. It is a parasite of numerous cultivated and wild cereals, forming sclerotia in the inflorescences of affected plants that look like black-violet horns. Sclerotia overwinter in the soil, and in the spring they germinate into stromas with perithecia, where ascospores are formed that infect cereals during their flowering period. Ergot sclerotia contain toxic alkaloids, and if they get into the grain during harvesting, and then into flour and flour products, poisoning, called ergotism, can occur. Ergotism manifests itself in two forms - gangrenous ("Antonov's fire") and convulsive ("evil writhing") and is due to the ability of ergot alkaloids to cause contractions of smooth muscles and their effect on the nervous system.
The first reports of this toxicosis are found on Assyrian cuneiform tablets dating back to 600 BC. It says that grains of bread may contain some kind of poison. In the past, ergotism was widespread in Europe and, during severe outbreaks, claimed a large number of victims. In the French chronicle of the late 10th century, for example, one of these outbreaks is described, during which about 40 thousand people died. In Russia, ergotism appeared much later than in Western Europe, and was first mentioned in the Trinity Chronicle in 1408. Nowadays, ergotism is observed in people extremely rarely. With the improvement of farming culture and the improvement of methods for purifying grain from impurities, this disease has become a thing of the past. However, interest in ergot continues unabated in our time. This is due to the widespread use of ergot alkaloids in modern medicine for the treatment of cardiovascular, nervous and some other diseases. Numerous alkaloids - derivatives of lysergic acid (ergotamine, ergotoxin, etc.) have been obtained from ergot sclerotia. The first chemically pure alkaloid was isolated in 1918, and in 1943 the chemical synthesis of lysergic acid diethylamide, an LSD drug that has a strong effect on the central nervous system and causes hallucinations, was carried out. To obtain ergot alkaloids, an ergot culture is used on rye in specially designated fields or a saprotrophic fungal culture on nutrient media.
Progress of medicine and mycology in the 20th century. made it possible to clarify the role of other fungal metabolic products that can cause dangerous toxicoses in humans and animals. Now the attention of specialists in the field of toxicology, veterinary medicine and mycology is drawn to poisoning caused by fungi growing on food and feed. Food products of plant and animal origin provide an excellent environment for the development of numerous fungi - we often encounter molding of products when they are stored improperly. Plant feed already becomes infected with fungi in natural conditions, as well as during storage, especially in unfavorable conditions. Developing on food and feed, microscopic fungi not only use the nutrients they contain, but also release mycotoxins, which can cause poisoning when such products are used as food.
Of the toxins of microscopic fungi, the most studied are aflatoxins, produced by some aspergillus - yellow, parasitic, etc. Numerous cases of human poisoning with aflatoxins are described in the literature. In 1968, 60 people died in Java after eating moldy peanut products. Even small doses of aflatoxins that do not cause acute poisoning are extremely dangerous, since these toxins have a carcinogenic effect - they can cause the development of malignant tumors of the liver and other organs.
Aspergillus yellows can cause dangerous toxicoses in humans and animals.
A large number of microscopic fungi are now known, primarily numerous species of penicillium and aspergillus, which produce dangerous toxins (ochra-toxins, rubratoxins, patulin, etc.). A large group of trichothecene toxins, formed by species of the genera Fusarium, Trichothecium, Myrothecium, etc., has been well studied. All these toxins are extremely diverse both in chemical structure and in their effect on the human and animal body. In recent years, many mycotoxins have been found to have carcinogenic and teratogenic effects - they can cause the formation of malignant tumors and, by disrupting the development of embryos, the appearance of various deformities in newborns (in animal experiments). The particular danger of toxins is that they are not only contained in the mycelium, but are also released into the environment, into those parts of the product where mycelium is absent. Therefore, moldy foods are extremely dangerous to eat even after the mold has been removed. Many mycotoxins can persist for a long time and are not destroyed by various food treatments.
Mushroom toxins
The poisonous properties of mushrooms were known to people already in ancient times. Even Greek and Roman writers reported on fatal mushroom poisonings, and history has brought down to this day the names of many famous personalities who became their victims. Among them are the Roman Emperor Claudius, the French King Charles VI, Pope Clement VII, etc. Already in ancient times, scientists tried to explain the nature of the poisonous effect of mushrooms. Greek physician Dioscorides in the middle of the 1st century. BC suggested that mushrooms get their poisonous properties from their environment, growing near rusty iron, decaying garbage, snake holes, or even plants with poisonous fruits. This hypothesis lasted for many years. It was supported by Pliny and many scientists and writers of the Middle Ages - Albert the Great, John Gerard and others. And only the high level of development of chemistry in the 20th century. allowed us to obtain the toxic substances contained in these mushrooms in their pure form, study their properties and establish their chemical structure.
Toxins of poisonous mushrooms are divided into three main groups based on the nature of the poisoning they cause. The first of them consists of substances with a local irritant effect, which usually cause disruption of the functions of the digestive system. Their effect manifests itself quickly, sometimes within 15 minutes, at the latest after 30-60 minutes. Many mushrooms that produce toxins of this group (some russula and lacticaria with a pungent taste, undercooked autumn honey mushrooms, satanic mushroom, variegated and yellow-skinned champignons, false puffballs, etc.) cause fairly mild, non-life-threatening poisoning that resolves within 2-4 days. However, among these mushrooms there are certain species that can cause life-threatening poisoning, for example, tiger row. There is a known case when a row of mushrooms (a single mushroom) that got into a mushroom dish caused severe poisoning in 5 people. There are also cases of mass poisoning with these mushrooms sold as champignons. Very toxic mushrooms are entoloma notched and some other types of entoloma. Symptoms of poisoning by tiger rower and poisonous entolomas are similar and resemble the symptoms of cholera: nausea, vomiting, severe loss of water from the body as a result of persistent diarrhea and, as a result of this, severe thirst, sharp abdominal pain, weakness and often loss of consciousness. Symptoms appear very quickly, within 30 minutes and no later than 1-2 hours after eating mushrooms. The disease lasts from 2 days to a week and in healthy adults usually ends with complete recovery. However, in children and people weakened by previous illnesses, the toxins of these fungi can cause death. The structure of toxins in this group has not yet been established. The second group includes toxins with a neurotropic effect, i.e., those that primarily cause disturbances in the activity of the central nervous system. Symptoms of poisoning also appear after 30 minutes - 1-2 hours: attacks of laughter or crying, hallucinations, loss of consciousness, indigestion. In contrast to the toxins of the first group, toxins with neurotropic effects have been studied quite well. They are found mainly in fly agarics - red, panther, cone-shaped, toadstool, as well as in some fibres, talkers, rowers, in very small quantities in bruises, russula emetic, some hebelomas and entolomas.
Research on the toxins of the red fly agaric began in the middle of the last century, and in 1869, German researchers Schmiedeberg and Koppe isolated an alkaloid from it, similar in its action to acetylcholine and called muscarine. Researchers assumed that they had discovered the main toxin of the red fly agaric, but it turned out that it is contained in this mushroom in very small quantities - only about 0.0002% of the mass of fresh mushrooms. Later, significantly higher contents of this substance were found in other mushrooms (in Patuillard fiber - up to 0.037%).
Under the influence of muscarine, a strong constriction of the pupils is observed, the pulse and breathing slow down, blood pressure decreases, and the secretory activity of the sweat glands and mucous membranes of the nose and mouth increases. A lethal dose of this toxin for humans, 300-500 mg, is contained in 40-80 g of Patouillard fiber and 3-4 kg of red fly agaric. In case of muscarine poisoning, atropine is very effective, quickly restoring normal heart function; With timely use of this drug, recovery occurs within 1-2 days.
The action of pure muscarine reproduces only the symptoms of peripheral phenomena observed during red fly agaric poisoning, but not its psychotropic effect. Therefore, the search for the toxin of this mushroom continued and led to the discovery of three active substances with psychotropic effects - ibotenic acid, muscimol and muscazone. These compounds are close to each other: muscimol, the main toxin of the red fly agaric, contained in it in the amount of 0.03-0.1% of the mass of fresh mushrooms, is a derivative of ibotenic acid. Subsequently, these toxins were discovered in other poisonous mushrooms - in the pineal and panther fly agarics (ibotenic acid) and in one of the rows (tricholomic acid - a derivative of ibotenic acid). It turned out that it is this group of toxins that causes the characteristic symptoms of red fly agaric poisoning - excitement, accompanied by hallucinations and, after some time, giving way to an anesthesia-like paralytic stage with prolonged deep sleep, severe fatigue and loss of consciousness. Ibotenic acid and its derivatives are similar in their effect on the body to atropine, therefore this remedy, used for muscarine poisoning, cannot be used for poisoning with red or panther fly agaric. In case of such poisoning, the stomach and intestines are cleansed and medications are given to relieve agitation and normalize cardiac activity and breathing. As with muscarine poisoning, the patient must be put to bed and a doctor must be urgently called. In the absence of qualified medical care, these toxins can cause the death of the patient.
The effect of these toxins is to a certain extent reminiscent of intoxication under the influence of alcoholic beverages. American researchers R. J. and V. P. Wasson, in the book “Mushrooms, Russia and History,” published in 1957, provide information about the use of this mushroom by the peoples of Siberia as a ritual remedy back in ancient times: under its influence a person came into a state of ecstasy and hallucinations. There are reports that in ancient Scandinavia there were special detachments of berserker warriors who, before battle, ate pieces of fly agaric or drank a drink from it
etc.................
Fruiting of ergot. Color micrograph of the fruiting bodies of ergot (Claviceps purpurea). This fungus attacks grain and wild cereals, reducing yield. Infection causes the affected plant tissue to grow and turn into a black mass called sclerotium. In this form, the mushroom survives the winter. In the spring, the sclerotium sprouts with capitate stroma, in which bags with spores are formed. Consumption of sclerotia in animals and humans causes severe poisoning, which can result in death. Symptoms of poisoning include vomiting, gangrene and hallucinations. Some medications, as well as LSD, are obtained from ergot.
The main causative agents of plant diseases are rust and smut fungi, which most scientists classify as basidiomycetes.
Rust mushrooms
A typical representative of this group is the linear rust of cereals (Puccinia graminis). It overwinters on stubble or unharvested straw in the form of special spores called telytospores, which germinate with the arrival of spring. On the resulting mycelium, normal basidiospores develop, which infect the leaves of the intermediate host - barberry. Here, the following type of spores (aecidiospores) are formed in huge quantities, with the help of which various cereals are infected, including wheat: characteristic symptoms appear on its leaves and stems - rusty or dark brown lines.
At this stage of the disease, spores of the third type (uredospores) develop, which are easily carried by the wind and infect new wheat plants, but are not able to germinate on barberry. The spread of infection and the appearance of new uredospores continues throughout the summer, and in the fall telytospores form again, and the circle closes. This development cycle is characteristic of many other rust fungi, which also have two host plants. However, some species undergo the entire cycle on a single host, such as blackberry rust (Phragmidium violaceum).
Rust fungi cause serious damage to plants such as coffee, various conifers, asparagus, legumes, garden carnations, etc. Huge amounts of money are spent on man's ongoing fight against fungi: new fungicides are constantly being developed and disease-resistant plant varieties are being developed.
Smut mushrooms
Smut fungi (order Ustilaginales) are also important plant pathogens, but their life cycle is not as complex as that of rusts and they never change hosts. Smut affects various grain crops and wild cereals, as well as many other flowering plants. The symptom of the disease is usually a dry, dusty, sooty coating. Spores most often develop within the ovaries of the host plant; for example, oats infected with smut (Ustilago avenae) produce a dusty mass of spores instead of seeds.
The well-known ergot (Claviceps purpurea), which grows in the ovaries of various cereals, including cereals, has in the past caused a severe and painful disease known as ergotism, or “evil writhing.” The fungus produces hard, black "horns" protruding from the plant's spikelets and consisting of tightly intertwined hyphae - called sclerotia. These sclerotia contain a number of very dangerous alkaloids that cause severe poisoning in animals and humans, which is accompanied by various symptoms and in many cases ends in death. Bread made from contaminated grain has killed many people in the past; Fortunately, modern grain harvesting and cleaning technologies, coupled with the use of fungicides, have made ergotism a very rare disease.
Other fungi that cause disease
Many other fungi cause skin diseases in humans, such as athlete's foot ("athlete's disease") and ringworm (these diseases are widely known throughout the world), as well as some rarer and less common diseases, which, however, can be very severe . These include blastomycosis and similar chronic lesions of deep tissues. Even cap mushrooms can infect the human body. Thus, the common slit leaf (Schizophyllum commune), which grows on wood and is distributed throughout the world, occasionally causes fungal diseases.
However, macromycetes are better known as destroyers of materials, especially as causative agents of wood rot, for example house fungi (Serpula lacrymans, etc.). These basidiomycetes are related to the familiar sponge fungi, but grow almost exclusively in buildings, forming prostrate mycelial films that quickly decompose wood, leading to the destruction of wooden structures. Other macromycetes are widely used by humans as food, but among them there are also poisonous species, which are discussed in more detail below.
Human diseases caused by fungi are called mycoses. They are superficial, subcutaneous and systemic (deep). There are also opportunistic mycoses that develop in weakened and immunodeficient individuals. In addition to mycoses, mushrooms can also cause mycotoxicosis in humans, that is, diseases that occur when consuming products contaminated with fungal toxins (mycotoxins). Superficial mycoses The causative agents of superficial mycoses are molds that can decompose the keratin of the epidermis, hair and nails. Based on the localization of the processes, keratomycosis (saprophytosis) and dermatomycosis are distinguished.
1. Keratomycosis. Keratomycosis is characterized by lesions of the stratum corneum of the epidermis and the surface of the hair shaft. Keratomycoses include lichen versicolor and tropical mycoses. 1.1. Lichen versicolor is a disease observed mainly in young people with excessive sweating, as well as diabetes. The causative agent is a yeast-like fungus Pityrosporum orbiculare. The skin most often affected is the armpits, back and chest. The disease manifests itself in the form of hyperpigmented or hypopigmented spots. When scraped off, the patches produce bran-like scales, which is why the condition is also known as pityriasis versicolor. Microbiological diagnosis includes microscopy of skin particles from lesions treated with alkali (KOH). The preparations reveal short curved hyphae and thick-walled yeast-like cells. When irradiating lesions with a Wood's lamp, a yellow glow is observed. After sowing the stratum corneum scales on Sabouraud's medium, whitish-cream shiny colonies appear in 4-8 days. For the treatment of versicolor versicolor, topical application of selenium sulfide and 1% terbinafine (Lamisil) cream is most effective.
1.2. Tropical mycoses.
1.2.1. Tinea nigricans. The causative agent of lichen nigricans is the mold Exophiala werneckii. The disease manifests itself as dark, painless spots on the palms and soles of the feet. There is no peeling. Affection is more common in children and young people in tropical regions.
1.2.2. Trichosporosis (white piedra). The causative agent of trichosporosis is the yeast-like fungus Trichosporon beigelii. Fungi infect the surface of the hair shafts, forming soft whitish-yellow nodules. The disease is more often recorded in countries with warm or tropical climates. When microscopying material from lesions, attention is paid to the presence of pseudohyphae, sometimes septate hyphae, numerous arthroconidia and a small number of blastoconidia. Amphotericin B is used for treatment, sometimes in combination with 5-fluorocytosine.
1.2.3. Black piedra. The causative agent is the mold Piedraia hortae. The disease is manifested by the formation of dense black nodules located on the hair of the head, beard and mustache. The disease is recorded in the humid tropical regions of South America and Indonesia. The pathogen is capable of both superficial and internal growth (along the hair shaft), which leads to increased hair fragility. For treatment, the hair on the affected areas is removed and the skin is treated with a surface fungicide (mercuric dichloride).
2. Dermatomycosis. In dermatomycosis, the epidermis, the skin itself, and the hair shaft are affected. Dermatomycosis is recorded everywhere, but more often in countries with a hot, humid climate. Infecting agents (fragments of hyphae and conidia) are transmitted by contact. Most often, infection occurs in baths, swimming pools and showers. Clinical manifestations. Skin lesions (dermatomycosis itself) are characterized by the formation of erythema, small papules, cracks and areas of peeling. Lesions of the scalp (trichomycosis) often manifest as brittle hair caused by the growth of the pathogen in the hair shaft. Nail lesions (onychomycosis) are characterized by their thickening and separation. Typically, nosological forms of dermatomycosis are distinguished according to their localization. At the same time, depending on the type of pathogen, trichophytosis, epidermophytosis and microsporia are distinguished. The Microsporum genus is a more common cause of tinea capitis, but can also affect other parts of the body. The hair falling out from the affected areas is surrounded by spores on the surface, and the skin scales contain many threads of mycelium. Infected hair fluoresces. Trichophyton causes ringworm of the scalp, beard, other areas of the skin and nails. Fungi are located as chains of spores within or on the surface of affected hair or as hyphae and characteristic spores in skin scales. Trichophyton schoenleini is the cause of almost all cases of favus (“scab”). Spores and mycelium threads are found in the crusts of the favus. The hair in the affected areas is filled with bubbles and channels in which the mycelium is hidden. Epidermophyton mainly causes ringworm of the skin of the body, hands and soles. With this disease, the threads of the fungus are located in the skin, the hair is not involved in the pathological process.
2.1. Dermatomycosis of the scalp (ring ringworm of the scalp) The main pathogens are mold fungi of the genera Trichophyton and Microsporum. The lesion is manifested by areas of baldness, peeling, sometimes erythema and pyoderma. The disease is more often registered in children. Can spread directly from person to person or through contaminated clothing. It is found in animals (dogs, cats), from which it can be transmitted to humans. The disease is accompanied by hair loss followed by filling of the hair follicles with dark conidia.
2.2. Juvenile lichen annulare is associated with patchy hair loss. This occurs spontaneously during puberty as the secretion of fatty acids by the glands of the scalp increases during this period. This form of lichen is transient and does not pose a threat. Lichen annulare appears as round, scaly lesions on the affected part.
2.3. Dermatomycosis of the beard and mustache (ring ringworm of the beard) is known as beard scabies (favus, scab) - an infectious lesion of the hair follicles (possibly granulomatous lesions); pathogen – Trichophyton schoenleinii; the main manifestations are papules and pustules on the skin of the face. 2.4. Dermatomycosis of the body - epidermophytosis, localized in various areas of the skin of the body; pathogens – Trichophyton mentagrophytes, T. rubrum and M. canis; characterized by peeling, pustular rashes, and sometimes erythema.
2.5. Inguinal dermatomycosis (ring ringworm of the groin area) is also called Arabian scabies. This is epidermophytosis, localized in the area of the external genitalia, inner thighs, perineum and groin areas; pathogens – Trichophyton mentagrophytes, T. rubrum, Epidermophyton floccosum and certain species of fungi of the genus Candida.
2.6. Athlete's foot (ring ringworm of the foot, or athlete's foot) - lesions of the sole area, mainly the skin of the interdigital spaces; characterized by small bubbles, cracks, areas of peeling and erosion. Similar lesions are observed on the upper extremities (athlete's foot); pathogens – Trichophyton mentagrophytes, T. rubrum, Epidermophyton floccosum.
2.7. Athlete's foot (onychomycosis) - fungal infection of the nails of the fingers and toes; pathogens are certain species of the genera Epidermophyton and Trichophyton. Microbiological diagnostics. Diagnosis of superficial mycoses is based on microscopy of affected tissues and identification of fungal cultures isolated from them. The causative agents of microsporia are quite easily identified by irradiating the hair with a Wood's UV lamp (the affected areas glow green). To isolate a pure culture, hair, fragments of skin and nails are used as research material. Samples are examined microscopically in unstained preparations treated with KOH. Isolation of cultures of the pathogen is carried out by placing individual hairs or pieces of skin on Sabouraud agar, Sabouraud agar with antibiotics, or potato dextrose agar. Trichophyton species grow in 2-3 weeks, the colonies are multi-colored, the conidia are large, smooth and septate (up to 10 septa), shaped like pencils (10-50 µm). Intraspecific identification is difficult and requires the study of biochemical properties. Microsporum species also grow slowly, the macroconidia are thick-walled, multicellular, spindle-shaped, 30-160 µm long and covered with spines. Epidermophyton floccosum produces white, yellow or olive colored colonies. Fungi are identified by the presence of many smooth, club-like conidia (7-20 µm long). Treatment. In the treatment of dermatomycosis, topical application of drugs containing sulfur, selenium, and tar is used. For onychomycosis, removal of the nail plate and cleansing of the nail bed are combined with the administration of griseofulvin and terbinafine.
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