Fungi

 

 

Fungi can be single celled or very complex multicellular organisms.  They are found in just about any habitat but most live on the land, mainly in soil or on plant material rather than in sea or fresh water.  A group called the decomposers grow in the soil or on dead plant matter where they play an important role in the cycling of carbon and other elements.  Some are parasites of plants causing diseases such as mildews, rusts, scabs or canker.  In crops fungal diseases can lead to significant monetary loss for the farmer.  A very small number of fungi cause diseases in animals.  In humans these include skin diseases such as athletes’ foot, ringworm and thrush.

Some pathogenic fungi that affects human beings and can cause important problems:  Aspergillus, Candida, Trichophyton, Microsporum, Malassezia Furfur, Blastocistis Homini, Hystoplasma Capsulatum and Pneumocystis Carinii.

Fungi are large organisms that usually live on dead and rotting animal and plant matter. They are found mostly in soil, on objects contaminated with soil, on plants and animals, and on skin, and they may also be airborne. Fungi may exist as yeasts or molds and may alternate between the two forms, depending on environmental conditions. Yeasts are simple cells, 3 to 5 micrometres (0.0001 to 0.0002 inch) in diameter. Molds consist of filamentous branching structures (called hyphae), 2 to 10 micrometres in diameter, that are formed of several cells lying end to end. Fungal diseases in humans are called mycoses; they include such disorders as histoplasmosis, coccidioidomycosis, and blastomycosis. These diseases can be mild, characterized by an upper respiratory infection, or severe, involving the bloodstream and every organ system. Fungi may cause devastating disease in persons whose defenses against infection have been weakened by malnutrition, cancer, or the use of immunosuppressive drugs. Specific types of antibiotics known as antifungals are effective in certain treatment.

Yeast, any of about 1,500 species of single-celled fungi, most of which are in the phylum Ascomycota, only a few being Basidiomycota. Yeasts are found worldwide in soils and on plant surfaces and are especially abundant in sugary mediums such as flower nectar and fruits. There are hundreds of economically important varieties of ascomycete yeasts; the types commonly used in the production of bread, beer, and wine are selected strains of Saccharomyces cerevisiae. Some yeasts are mild to dangerous pathogens of humans and other animals, especially Candida albicans, Histoplasma, and Blastomyces. As fungi, yeasts are eukaryotic organisms. They typically are …(100 of 333 words).

 

 

Mold, also spelled mould, in biology, a conspicuous mass of mycelium (masses of vegetative filaments, or hyphae) and fruiting structures produced by various fungi (kingdom Fungi). Fungi of the genera Aspergillus, Penicillium, and Rhizopus form mold and are associated with food spoilage and plant diseases.

Mycosis, plural Mycoses, in humans and domestic animals, a disease caused by any fungus that invades the tissues, causing superficial, subcutaneous, or systemic disease. Superficial fungal infections, also called dermatophytosis, are confined to the skin and are caused by Microsporum,Trichophyton, or Epidermophyton; athlete’s foot, for example, is caused by Trichophyton or Epidermophyton. Subcutaneous infections, which extend into tissues and sometimes into adjacent structures such as bone and organs, are rare and often chronic.  Candidiasis (Candida) may be a superficial infection (thrush, vaginitis) or a disseminated infection affecting certain target organs, such as the eyes or kidneys. Painful ulcerations and nodules appear in subcutaneous tissues in sporotrichosis (Sporothrix). In systemic fungal infections fungi may invade normal hosts or immunosuppressed hosts (opportunistic infections). Cryptococcosis (Cryptococcus) and histoplasmosis (Histoplasma) are marked by respiratory distress.

Effective therapy against the invasive fungi is limited because the same antibiotics that interfere with fungi also attack the host’s cells. Griseofulvin has met with some success in the treatment of superficial mycoses.  Amphotericin B and flucytosine have also been used in treating the subcutaneous and systemic mycoses.

 

 

 

Histoplasmosis, infection with the fungus Histoplasma capsulatum, occurring in humans and other animals. The disease is contracted by the inhalation of dust containing spores of the fungus. H. capsulatum prefers moist, shady conditions and is found in woods, caves, cellars, silos, and old chicken houses. The last seem to be especially important because chickens often are infected and pass enormous numbers of organisms in their droppings. The use of chicken manure in gardens may lead to histoplasmosis in humans. Dogs, rats, mice, bats, pigeons, skunks, and probably many other animals become infected and may help to spread the disease. The chief site of infection is the lungs, though the fungus can spread through the bloodstream to other organs, such as the liver, and bone marrow.

There are three forms of the disease. The primary acute form involves only the lungs and causes symptoms of fever, coughing, and chest pain. The infection may be slight and is often asymptomatic. In the progressive disseminated form of histoplasmosis, the infection spreads to the liver, spleen, or adrenal glands, where it causes lesions and damages those organs. In the third form, chronic cavitary disease, the infection remains in the lungs but damages them more seriously, causing coughing and severe shortness of breath. All three forms can produce symptoms that are indistinguishable from those caused by other acute respiratory infections such as pneumonia and pneumonitis—i.e., coughing, chest pain, difficulty in breathing, fever, chills, and fatigue. X-ray examination of the lungs may show a localized shadow or a more diffuse mottling of the lungs. In most cases, however, infection with H. capsulatum causes no symptoms or discomfort at all. Diagnosis is made by serological tests or by culture of the organism. Most cases do not require treatment, but patients with widespread disease can be treated with the antibiotic amphotericin B.

Histoplasmosis is worldwide in distribution and is endemic in parts of the east-central United Statesand the Mississippi River valley. Infants and men past middle age show the least resistance to symptomatic infection, but 50 to 80 percent of the total population of endemic areas show positive skin tests.

Blastomycosis, infection of the skin and viscera caused by fungal organisms of the genus Blastomyces. There are two major types of blastomycosis: the North American, caused by B. dermatitidis, and the South American, caused by B. brasiliensis. In North American blastomycosis, skin and lung lesions are most common: pulmonary lesions vary in size from granulomatous nodules to confluent, diffuse areas of pus-forming inflammation involving the entire lobe of the lung. In the skin, micro-abscesses lie just beneath the epidermis, the outermost layer of the skin, and are associated with a granulomatous appearance of the surrounding skin.

In South American blastomycosis, the portal of entry is usually the nasopharynx (the part of the alimentary canal between the cavity of the mouth and the esophagus that is continuous with the nasal passages); swelling and ulceration of the mouth or nose may cause the infection to spread to the nearby lymph nodes; primary lesions may also occur in the lymphoid tissues in the lower abdomen. In both North and South American varieties, the infection may spread not only to the lymph nodes but also to such organs as the brain, bones, liver, spleen, and adrenals.