Histoplasma
Histoplasma/ Histoplasmosis capsulatum
Causative Agent: Histoplasma is a genus of dimorphic fungi (def.) and it contains a few species such as Histoplasma farciminosum, which causes epizootic lymphangitis (def.) in horses; Histoplasma capsulatum, which causes a fungal infection called histoplasmosis in human. Because H. capsulatum is most prevalent in Ohio and histoplasmosis is quite a common disease in this area, the disease is also known as Ohio Valley’s disease. There are three major types of histoplasmosis: acute, chronic and progressive disseminated. It primarily infects the lungs but sometimes, other organs are also infected through the blood stream and in this case, a patient is said to have disseminated histoplasmosis, and this form of infection may become fatal if left untreated. Histoplasma capsulatum is a thermal dimorph due to its capacity to form different structures at different temperatures. In nature in the moist soil that is rich in bird or bat guano (def.) at temperature about 25 degree C, it has a mycelial (filamentous) form with macroconidia (def.) as well as microconidia (def.) spores that can be inhaled and may reach the lung alveoli (def.). At body temperature at about 37 degree C, it morphs into small budding yeasts about 2-5 um in diameter. In most cases, the macrophage response kills the yeast but sometimes, H. capsulatum yeast phase helps it gets around the human immune system. A following change in the chemicals composition of the fungal cell wall also occurs as the phase shift, and thus the antigens change and the immune system retools, which enables the fungus to establish in the lungs.
Epidemiology: Histoplasmosis is the most common endemic fungal infection in the U.S. with about 250,000 cases diagnosed per year. Although H. capsulatum can be found throughout the world, it is most prevalent in certain areas of the United States. According to skin tests, the largest area with high
Causative Agent: Histoplasma is a genus of dimorphic fungi (def.) and it contains a few species such as Histoplasma farciminosum, which causes epizootic lymphangitis (def.) in horses; Histoplasma capsulatum, which causes a fungal infection called histoplasmosis in human. Because H. capsulatum is most prevalent in Ohio and histoplasmosis is quite a common disease in this area, the disease is also known as Ohio Valley’s disease. There are three major types of histoplasmosis: acute, chronic and progressive disseminated. It primarily infects the lungs but sometimes, other organs are also infected through the blood stream and in this case, a patient is said to have disseminated histoplasmosis, and this form of infection may become fatal if left untreated. Histoplasma capsulatum is a thermal dimorph due to its capacity to form different structures at different temperatures. In nature in the moist soil that is rich in bird or bat guano (def.) at temperature about 25 degree C, it has a mycelial (filamentous) form with macroconidia (def.) as well as microconidia (def.) spores that can be inhaled and may reach the lung alveoli (def.). At body temperature at about 37 degree C, it morphs into small budding yeasts about 2-5 um in diameter. In most cases, the macrophage response kills the yeast but sometimes, H. capsulatum yeast phase helps it gets around the human immune system. A following change in the chemicals composition of the fungal cell wall also occurs as the phase shift, and thus the antigens change and the immune system retools, which enables the fungus to establish in the lungs.
Epidemiology: Histoplasmosis is the most common endemic fungal infection in the U.S. with about 250,000 cases diagnosed per year. Although H. capsulatum can be found throughout the world, it is most prevalent in certain areas of the United States. According to skin tests, the largest area with high
Citations: Center for disease Control and Prevention. National Center for Zoonotic, Vector-Borne, and Enteric Diseases. Histoplasmosis. Web. April 15th, 2011. http://www.cdc.gov/nczved/divisions/dfbm/diseases/histoplasmosis/#who ADAM Health Illustrated Encyclopedia. Healthline. Histoplasmosis-Disseminated. Web. April 16th, 2011. http://www.healthline.com/adamcontent/histoplasmosisdisseminated?utm_source=fungal%20infection%20of%20lung&utm_ad=histoplasmosis&utm_medium=googleutm_campaign=adam&utm_term=histoplasmosis%20epidemiology Ajello, Libero. Cheng, Shu-lan. Sexual Reproduction in Histoplasma capsulatum. Science 31 March 1967: Vol. 155 no.3770 p. 1696. April 18th, 2011. http://www.sciencemag.org/content/155/3770/1696.2.citation Davis, Charles. MedicineNet. Histoplasmosis. Web. April 18th, 2011. http://www.medicinenet.com/histoplasmosis/page6.htm#information