The bovine viral diarrhea virus (BVDV) is not limited to bovines. BVDV, and related pathogens classed as “pestiviruses,” can infect wild ruminants, which could serve as reservoirs of disease for transmission back to cattle.
During the recent BVDV symposium in Kansas City, Auburn University veterinarian Thomas Passler, DVM, PhD, presented research led by Peregrine Wolff, a wildlife veterinarian with the Nevada Department of Wildlife. Passler outlined how work in Nevada and elsewhere has shown that pestiviruses, including type 1 and type 2 BVDV, sometimes circulate in populations of wildlife including whitetail deer, mule deer, bighorn sheep and mountain goats. Researchers also have found the pronghorn virus, a pestivirus so named because it was originally isolated from pronghorn antelope, in deer and bighorn sheep.
Studies of BVDV in whitetail deer have shown that clinical signs are similar to those found in cattle, and that exposure in does during early gestation can result in production of persistently infected (PI) fawns. If a PI fawn survives, it will shed the virus continuously and potentially spread the disease, as happens with PI cattle. Deer-to-deer transmission has been shown to occur, but researchers are unsure of whether deer transmit the disease back to cattle.
Researchers also have found BVDV in some western populations of mule deer, and Passler notes that in migratory herds of mule deer, the animals tend to “stage” or gather for migration at a time that corresponds with the first trimester of gestation, potentially increasing the chance of exposure and the creation of PI fawns.
Several areas in the West have recently experienced die-offs of Rocky Mountain bighorn sheep due to respiratory disease. In some of these cases, diagnosticians have isolated BVDV, along with respiratory pathogens such as PI3, BRSV and mycoplasma. In cattle, BVDV is known to be immunosuppressive, and is linked to respiratory disease involving bacterial pathogens. These findings suggest a similar process could be occurring in these die-offs of bighorn sheep.
Passler notes that controlling or eradicating BVDV in wild-animal populations would be extremely difficult. He says the burden will fall on ranchers to vaccinate their cattle, quarantine and test imported animals and work with their veterinarians to keep BVDV out of their herds and stop it quickly if cases occur. A systematic BVDV control program in cattle can help prevent transmission of the virus to wildlife, potentially preventing future reintroduction of the disease to domestic herds.