VACCINATION OF PRONGHORN ANTELOPE (ANTILOCAPRA AMERICANA PENINSULARIS) WITH AN INACTIVATED BLUETONGUE VIRUS VACCINE ELICITS VIRUS-NEUTRALIZING ANTIBODY RESPONSE AND POSSIBLE PROTECTION UNDER FIELD CONDITIONS.

Abstract

Pronghorn antelope (Antilocapra americana peninsularis) are susceptible to bluetongue virus (BTV) infection. In infected animals, the virus causes acute hemorrhagic disease with a mortality rate exceeding 50 percent. The Baja Peninsular pronghorn antelope is an endangered subspecies of pronghorn in North America with the population declining since 1990. The objective of this study was to evaluate safety and virus-neutralizing (VN) antibody production of an inactivated vaccine containing three serotypes of BTV (BTV-10, 11 and 17) in pronghorn antelope kept in captivity. The vaccine was administered subcutaneously to 13 antelope (three male, 10 females; <1year to 11years of age) followed by a booster dose after one month. Serum samples collected prior to the first vaccination and at one-month post-booster were evaluated for seroconversion using a virus-neutralization assay. For vaccination, blood collection and post-vaccination injection site examination the animals were caught and physically restrained. Antibody titers against BTV serotypes 10, 11, and 17 respectively were at least twofold higher than the corresponding pre-vaccination samples in 4/5 (80%) juveniles and 4/5 (80%) adults. In adults, the post-vaccination VN antibody titer means for the three BTV serotypes were two to four times higher than the pre-vaccination titer means, whereas in the juveniles, post-vaccination VN antibody titer means were less than or equal to two times higher than the pre-vaccination titer means. Fifteen months after the administration of the second dose of the vaccine, one of the two adult male unvaccinated control antelope housed along with the vaccinated antelope developed clinical signs of BTV infection and died of the disease. BTV serotypes 11 and 17 were confirmed by RT-PCR. None of the 13 vaccinated antelope developed clinical signs of BTV infection, suggesting that they were protected by the vaccine. The vaccine was also found reasonably safe for use in this species. Mild to moderate injection site reactions leading to the formation of firm masses were seen in about 30.7% of the vaccine injection sites after administering the vaccine through the sub-cutaneous route. Except one, all local injection site reactions and lesions were healed in two to eight weeks without further complications.