Abstract
Infection with the saprophytic fungus Coccidioides immitis typically results in subclinical or self-limiting infections with granulomas in the lungs and local lymph nodes.3 The Zoological Society of San Diego maintains a herd of Przewalski’s horses at the Wild Animal Park that are part of the global captive breeding population. Because of an apparent high prevalence of coccidioidomycosis in this herd,2 necropsy records and slides from Przewalski’s horses (n=30, 15 males, 15 females) greater than 1 month of age that died between 1984 and 2000 were reviewed. Coccidioidomycosis was the single leading cause of death in this population, resulting in the death of 33% of these horses. Affected horses tended to be younger (average age 2.5 years) than unaffected animals (average age 13.1 years) at the time of death and males were overrepresented (eight males, two females). Affected animals were housed in multiple enclosures. Although the founder base for the Przewalski’s horse is limited, multiple lineages appear to be affected and, in most cases, the dams, sires, and half siblings of affected animals were not affected. Lesions in affected horses included chronic granulomas in the lungs and tracheobronchial lymph nodes of all animals with variable involvement of the brain, spinal cord, liver, kidney, skeletal muscle, spleen and other regional lymph nodes.
To determine if this high prevalence was the result of species predisposition or environmental factors, necropsy records from other species of equids housed at the Wild Animal Park that had died during this same time period were also reviewed. During this same time period, only two individual animals from populations of Somali wild ass (Equus africanus somalicus) (n=5), Grevy’s zebra (Equus grevyi) (n=19), Transcaspian kulan (Equus hemionus kulan) (n=15), Persian onager (Equus hemionus onager) (n=31), and Eastern kiang (Equus kiang holdereri) (n=6) had pulmonary granulomas due to infection with C. immitis. No equids other than the Przewalski’s horses were diagnosed with systemic coccidioidomycosis.
Because systemic coccidioidomycosis rarely occurs in domestic animals with adequate cell-mediated immune function,1,3,4 studies are ongoing to evaluate the immune function of Przewalski’s horses. The number and distribution of CD21+ B cells and CD3+ T cells including CD4 (helper) and CD8 (cytotoxic) T-cell subsets were quantified in circulating blood of Przewalski’s horses (n=4) using flow cytometry. Preliminary analysis suggests that lymphocyte profiles in Przewalski’s horses are similar to those in domestic horses. Studies are ongoing to evaluate immune function and specific responses to C. immitis antigens of Przewalski’s horses in comparison to domestic horses.
Literature Cited
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2. Boyd, L., and K.A. Houpt. 1994. Veterinary Care. In: Przewalski’s Horse: The history and biology of an endangered species. State University of New York Press; Albany, New York: 143–172.
3. Hirsh, D.C., and Y.C. Zee. 1999. Agents of systemic mycosis. In: Veterinary Microbiology. Blackwell Science; Malden, Massachusetts: 256–259.
4. Kirkland, T.N., and J. Fierer. 1996. Coccidioidomycosis: a reemerging infectious disease. Emerging Inf Dis. 2:192–199.