Testicular lesions and antler abnormalities in Colorado, USA mule deer (Odocoileus hemionus): a possible role for epizootic hemorrhagic disease virus.

Antler abnormalities of deer and other cervids often result from testicular lesions and decreased levels of testosterone, inhibiting normal cycles of antler growth. Affected males have antlers with retained velvet, numerous short, misshapen points ("cactus bucks"), and failure to shed these abnormal antlers annually. In Colorado, US, we observed a high occurrence of "cactus bucks" in mule deer (Odocoileus hemionus) populations after management efforts to increase the number of mature male deer in the state. Affected males consistently had antibody to epizootic hemorrhagic disease virus serotype 2 (EHDV-2), and examination of the testes of these animals demonstrated nonspecific end-stage lesions of chronic inflammation, fibrosis, and mineralization. To examine more acute stages of testicular lesions, and to screen for EHDV specifically within the testes, we sampled 16 male mule deer from affected herds, but with essentially normal antlers (n = 14) or retained velvet only (n = 2). Testicular and epididymal lesions identified from these samples included necrotizing vasculitis (n = 2), hemorrhage (n = 6), edema (n = 2), seminiferous tubular necrosis (n = 5), orchitis (n = 5), epididymitis (n = 10), hypospermia (n = 6), and end-stage lesions of seminiferous tubular loss (n = 2), fibrosis (n = 2), and mineralization (n = 2). Each of the 16 cases was blindly scored on the basis of number of histologic lesions, with a median score of two. Five of seven (71%) testes that were PCR positive for EHDV had lesion scores above the median, whereas none of the nine (0%) EHDV PCR-negative testes had lesion scores above the median, suggesting an association between testicular lesions and detection of EHDV RNA in the testes (P = 0.003). Although the role of EHDV infection remains unconfirmed, the association between testicular and epididymal lesions and presence of EHDV RNA in the affected tissues suggests that cactus buck antlers may be a sequela of EHDV infection.