Coccidioides posadasii
| Coccidioides posadasii | |
|---|---|
| Scientific classification | |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Class: | Euascomycetes |
| Order: | Onygenales |
| Family: | Onygenaceae |
| Genus: | Coccidioides |
| Binomial name | |
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Coccidioides posadasii |
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Coccidioides posadasii is a pathogenic fungus that, along with Coccidioides immitis, is the causative agent of coccidioidomycosis, or valley fever in humans. It resides in the soil in certain parts of the Southwestern United States, northern Mexico, and some other areas in the Americas, but its evolution was connected to its animal hosts.
C. posadasii and C. immitis are morphologically identical, but genetically and epidemiologically distinct.C. posadasii was identified as a separate species other than C. immitis in 2002 after a phylogenetic analysis. The two species can be distinguished by DNA polymorphisms and different rates of growth in the presence of high salt concentrations: C. posadasii grows more slowly. It is also differs epidemiologically, since it is found outside the San Joaquin Valley. Unlike C. immitis, which is geographically largely limited to California, C. posadasii can also be found in northern Mexico and South America.
As an intern in Buenos Aires in 1892, Alejandro Posadas described an Argentine soldier that had a dermatological problem since 1889. Posadas had seen the patient while a medical student in 1891 and skin biopsies revealed organisms resembling the protozoan Coccidia. The patient died in 1898 but during the interim Posadas successfully transmitted the infection to a dog, a cat, and a monkey, by inoculating them with material from his patient.
In 1899 a 40 year old manual laborer from the San Joaquin Valley, a native of the Azores, entered a San Francisco hospital with fungating lesions similar to those of Posadas' patient. Dr. Emmet Rixford, a surgeon at San Francisco's Cooper Medical College, in attempts to determine the cause, concluded it was not from inadvertent self-inoculation. Further research produced a chronic ulcer in a rabbit and a lesion in a dog both excreting pus with the same organisms. Rixford issued a report, co-authored by Dr. Thomas Caspar Gilchrist (1862-1927), that was printed in 1896, one year after the patient died. A pathologist at Johns Hopkins Medical School and Gilchrist studied the material and determined the microbe was not a fungus but a protozoan resembling Coccidia. With the help of parasitologist C.W. Stiles, the organism was named Coccidioides (“resembling Coccidia”) immitis (“not mild”). Four years later William Ophüls and Herbert C. Moffitt proved that C. immitis was not a protozoan but was a fungus that existed in 2 forms. In 1905 Ophüls called the infections "coccidioidal granuloma" and that it could develop from inhalation of the organism. Also in 1905 Samuel Darling studied a case and, referring to the misnamed organism a protozoan, named it Histoplasma capsulatum, meaning three major endemic fungi in the United States were all initially misidentified as protozoa.
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