Fungal Infections of Human and Animals
Many fungal infections, or mycoses, of humans and animals affect only the outer layers of skin, and although they are sometimes difficult to cure, they are not considered dangerous. Athlete's foot and ringworm are among the common superficial fungal infections. Fungal infections of the mucous membranes are caused primarily by Candida albicans (see candidiasis). It usually affects the mouth (see thrush) and the vaginal and anal regions.
The fungi that affect the deeper layers of skin and internal organs are capable of causing serious, often fatal illness. Sporotrichosis is an infection of farmers, horticulturists, and others who come into contact with plants or mud. The disease affects the skin and lymphatic system and, in rare cases, becomes disseminated. Blastomycosis is caused by a yeastlike fungus that reproduces by budding. The North American variety, caused by Blastomycosis dermatitidis, occurs more often in men and seems to be limited to the central and E United States and Canada. Wartlike lesions appear most often on the skin, sometimes spreading to the bones and other organs. The South American variety of blastomycosis is caused by B. brasiliensis. Chytridiomycosis, caused by Batrachochytrium dendrobatidis, is a deadly fungal skin infection in amphibians, which it kills by damaging to the animals' normally permeable skin, thus disrupting the transport of air and moisture.
Among the fungi that infect the deeper tissues is Coccidioides immitis, which causes coccidioidomycosis, sometimes called valley fever, a lung infection that is prevalent in the SW United States. Cryptococcosis is another fungus disease that may be localized in the lung or disseminated, especially to the central nervous system. It has a worldwide distribution, affecting men twice as often as women. The causative agent (Cryptococcus neoformans) has been isolated in pigeon excretions. Histoplasmosis, which is caused by spores of the fungal genus Histoplasma, is a severe infection that shows varied symptoms. In acute cases ulcers of the pharynx and enlargement of the liver and spleen are present. In other forms tubercularlike lesions of the lung occur. In its benign form no symptoms may be present.
Fungal infections sometimes follow the use of antibiotics, which kill nonpathogenic as well as pathogenic bacteria, thereby providing a free field in the body for fungal invasion. Opportunistic fungal infection occurs when a fungus enters a compromised host, as in the case of such diseases as AIDS. Treatment for fungal infections includes systemic antifungal agents, such as amphotericin B, fluconazole, and itraconazole, and agents usually used topically, such as clotrimazole (Lotrimin) and miconazole (Monistat).
Fungal Infections of Plants
Serious damage is done to crops each year by fungal infections of plants such as smuts, rusts, ergots, and mildews. Dutch elm disease, a disease that has seriously depleted the number of elm trees in the United States, is caused by the fungus Ceratostomella ulmi. Such diseases are usually fought with fungicides or by developing resistant plants. See also diseases of plants.
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Classification
Mycoses are classified according to the tissue levels initially colonized:Superficial mycoses
Superficial mycoses - limited to the outermost layers of the skin and hair.An example of a fungal infection is Tinea versicolor: Tinea versicolor is a fungus infection that commonly affects the skin of young people, especially the chest, back, and upper arms and legs. Tinea versicolor is caused by a fungus that lives in the skin of almost all adults. It doesn't usually affect the face. This fungus produces spots that are either lighter than the skin or a reddish-brown. There may be just a few spots or lots of spots. This fungus exists in two forms, one of them causing visible spots. Factors that can cause the fungus to become more visible include high humidity, as well as immune or hormone abnormalities. However, almost all people with this very common condition are healthy.
Cutaneous mycoses
Cutaneous mycoses - extend deeper into the epidermis, as well as invasive hair and nail diseases. These diseases are restricted to the keratinized layers of the skin, hair, and nails. Unlike the superficial mycoses, host immune responses may be evoked, resulting in pathologic changes expressed in the deeper layers of the skin. The organisms that cause these diseases are called dermatophytes. The resulting diseases are often called ringworm (even though there is no worm involved) or tinea. Cutaneous mycoses are caused by Microsporum, Trichophyton, and Epidermophyton fungi, which together comprise 41 species.Subcutaneous mycoses
Subcutaneous mycoses - involve the dermis, subcutaneous tissues, muscle, and fascia. These infections are chronic and can be initiated by piercing trauma to the skin, which allows the fungi to enter. These infections are difficult to treat and may require surgical interventions such as debridement.Systemic mycoses due to primary pathogens
Systemic mycoses due to primary pathogens - originate primarily in the lungs and may spread to many organ systems. Organisms that cause systemic mycoses are inherently virulent. Generally, primary pathogens that cause systemic mycoses are dimorphic.Systemic mycoses due to opportunistic pathogens
Systemic mycoses due to opportunistic pathogens - infections of patients with immune deficiencies who would otherwise not be infected. Examples of immunocompromised conditions include AIDS, alteration of normal flora by antibiotics, immunosuppressive therapy, and metastatic cancer. Examples of opportunistic mycoses include Candidiasis, Cryptococcosis and Aspergillosis.Treatment
Antifungal drugs are used to treat mycoses. Depending on the nature of the infection, a topical or systemic agent may be used. Photochemotherapy or photopheresis is a technique used at major medical centers for the treatment of mycosis fungoides.Prevention
Keeping the skin clean and dry, as well as maintaining good hygiene, will help prevent topical mycoses. Because fungal infections are contagious, it is important to wash after touching other people or animals. Sports clothing should also be washed after use. Wearing flip-flops when using a community swimming pool or shower will also prevent topical infections.References
External links
- Guide to Fungal Infections - Patient-oriented, educational website written by dermatologists.
- Doctor Fungus - An educational website sponsored through unrestricted educational grants by numerous pharmaceutical companies
This article is licensed under the GNU Free Documentation License.
Last updated on Monday July 21, 2008 at 13:24:12 PDT (GMT -0700)
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