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Blastomycosis is caused by the fungus Blastomyces dermatitis. The disease can manifest itself as a chronic cutaneous lesion, an acute or chronic pneumonia, or a systemic infection. The disseminated form of the disease can affect almost any tissue or organ, but most frequently affects the skin, bones, or genitourinary tract. Exposure usually occurs during recreational activities, and disease results from the inhalation of infective particles from the environment. The organism is found in soil containing decaying organic matter. Blastomyces dermatitis is a dimorphic fungi, which produces characteristic large, broad-like, unipolar budding yeast-like cells at 37癈.
Aspergillosis is a spectrum of diseases caused by species of the fungal genus Aspergillus. The major species causing aspergillosis are Aspergillus fumigatus; Aspergillus flavus; Aspergillus niger; and Aspergillus terreus. The Aspergillus can cause allergy, colonization, toxicoses, and tissue invasion. Tissue invasive, or disseminated, is especially common in patients that are immunocompromised. Pulmonary aspergillosis can manifest itself initially as an allergic process, which can result in the formation of 揻ungus balls?in pre-existing lung cavities. A vigorous immune response can occur. This can progress to a severe hemoptysis and invasive disease. The invasive form of aspergillosis is a serious and life threatening disease. The culture of Aspergillus produces characteristic fruiting heads.
Coccidioidomycosis is caused by the fungus Coccidioides immitis. It is an infectious disease usually acquired by inhalation of arthroconidia or rarely by their traumatic introduction through the skin. The disease initially is usually a respiratory infection resulting from the inhalation of conidia that typically resolves rapidly leaving the patient with a strong specific immunity to re-infection. There are however, some individuals where the disease progresses to a chronic pulmonary form or systemic form involving the meninges, bones, joints, and subcutaneous and cutaneous tissues. The organism is a normal inhabitant of the soil and is endemic in the south-western United States, northern Mexico, and various centers of South America. The fungus is dimorphic and at 25癈 produces diagnostic alternate arthroconidia that are typically single celled, rectangular to barrel-shaped, separated from each other by a disjunctor cell.
Histoplasmosis is caused by the fungus Histoplasma capsulatum. There are three subspecies, var. capsulatum; var. duboisii; and var. farciminosum. All infections have an environmental source, specifically habitats enriched with the feces of gregarious birds and bats. The fungus is dimorphic. Infections are acquired by the inhalation of airborne microconidia. There are three broad clinical forms found in the symptomatic patient. These are acute pulmonary; disseminated; and chronic pulmonary. The fungus has a predilection for cells of the reticuloendothelial system (bone marrow, liver, lymph nodes, spleen, and adrenal glands). Systemic spread may produce cutaneous and subcutaneous lesions after hematogenous dissemination. X-rays reveal diffuse densities in the lungs. Blood and bone marrow smears contain abnormal numbers of macrophages filled with tissue form yeast cells. Microconidia are found abundantly in feces contaminated soil along with the strikingly ornamental tuberculate macroconidia that is microscopically diagnostic for histoplasmosis.
Paracoccidioidomycosis is caused by the fungus Paracoccidioides brasiliensis. It is a systemic, granulomatous and suppurative mycosis. The organism is found naturally in soil, rivers, or lakesides in subtropical regions of Latin America. Infections are acquired by the inhalation of spores. The organism can be seen in biopsy specimens of affected tissue, pus, or bronchial washings. A dimorphic fungus, the yeast form has characteristic single and multiple-budding yeast cells. The multiple-budding cells are thick-walled and 10 to 25um in diameter with buds from 1 to 10um in diameter (called 揗ariners Wheel?.
Cryptococcosis is caused by Cryptococcus neoformans, which is an opportunistic yeast. It is the most common agent causing central nervous system and systemic infection in patients with HIV. Cryptococcus neoformans meningitis usually begins as an asymptomatic pulmonary infection that progresses to fungemia and meningitis in the immunocompromised individual. The organism can then disseminate throughout the body and infect any organ. The organism抯 natural habitat is the soil and is found to grow well in pigeon droppings. Areas with an abundance of pigeons are particularly good sources of infection for these individuals. The India ink prep is a quick test that can be used to detect the presence of Cryptococcus neoformans in the CSF. The organism has a large capsule surrounding it that is impenetrable to the India ink and thus a clearing is seen around the organism when examined microscopically. However, the test has limited sensitivity. Antigen detection tests are more sensitive but the turn-around time is considerably longer. The organism has only a yeast phase and thus is not dimorphic. |
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