Coccidioidomycosis in Przewalski’s horses (Equus przewalskii).

The research investigated coccidioidomycosis, a rare fungal infection, in Przewalski’s horses and found that these horses potentially possess weaker immune responses to the disease compared to domestic horses.

Objective and Methodology

• The study was driven by an observed high incidence of coccidioidomycosis, an infection caused by the fungus Coccidioides immitis, in Przewalski’s horses at a specific facility.
• The researchers examined necropsy records and biomaterials from 30 horses, 15 males and 15 females, that died between 1984 and 2000.
• For comparison, data from other exotic equids, 76 in total, housed at the same facility during this period were also analyzed.
• Blood analyses to quantify lymphocyte subsets and conduct lymphocyte blastogenesis assays were carried out to examine the immune response.

Findings and Interpretation

• Coccidioidomycosis was identified as the leading cause of death, implicated in 33% of cases, indicating a higher susceptibility in Przewalski’s horses.
• Fungal lesions were mainly found in the lungs and tracheobronchial lymph nodes, but variable involvement of multiple other organs were observed, underlining the systemic nature of the disease.
• The affected horses tended to be younger than unaffected ones, indicated multiple lineages were susceptible, and had a higher incidence in males, suggesting potential genetic and sex-related influences.
• No other exotic equids in the same facility were diagnosed with coccidioidomycosis during the same period, implying specific vulnerability in Przewalski’s horses rather than purely environmental factors.
• The number of lymphocyte subsets (CD3, CD4, CD5, CD8, CD21+ cells), cells pivotal to the immune response, were similar in both Przewalski’s horses and domestic horses.
• However, lymphocytes from two of the Przewalski’s horses failed to proliferate in response to Coccidioides. One of these horses had systemic disease and the other developed coccidioidomycosis 2 years later.
• This suggested that certain Przewalski’s horses might have an inadequate immune response to Coccidioides, leading to a higher susceptibility to coccidioidomycosis.

In conclusion, the research signified that a potentially weaker immune response is likely to contribute to higher incidents of coccidioidomycosis in Przewalski’s horses compared to other equids.