Safety Evaluation of Inactivated Polyvalent Vaccine Against Bluetongue Virus Serotypes 10, 11, and 17 in Pregnant Ewes

Abstract

Bluetongue is a noncontagious, vector-borne Orbivirus-induced disease of domestic and wild ruminants. Both live and inactivated monovalent vaccines are used to control bluetongue disease worldwide. The objective of this study was to evaluate the safety and post-vaccination seroconversion of an inactivated polyvalent bluetongue virus (BTV) vaccine containing serotypes 10, 11 and 17 in pregnant ewes. The vaccine was evaluated by vaccinating 66 pregnant ewes (33 for each study group). The ewes enrolled for this study represented 24 dairy, 30 meat, and 12 crossbreds and were aged 1-9 years. The average body weight of the animals ranged from 73 to 82 kg. Pregnant ewes representing all three trimesters of pregnancy were used in this study. Each animal was vaccinated with a 2.0 ml dose of the vaccine subcutaneously. All ewes were revaccinated similarly after one month. Local injection site reactions after both vaccinations, systemic and other adverse reactions, effects on pregnancy, fetal development, delivery of the lambs, and post-vaccination virus-neutralizing (VN) antibody titers were monitored after each vaccination. Mild to moderate injection site reactions such as swelling or lump formation were seen in 29 injection sites (22.0%). All injection site reactions were resolved completely within 2 – 7 weeks without further complications and treatment. Mild to moderate post-vaccination systemic reactions such as anorexia/lethargy/laminitis were seen only in two ewes, which lasted for four days. Bluetongue vaccination in the pregnant ewes did not affect the pregnancy, fetal development, and delivery of the lambs. There were no premature abortions or any form of teratogenic deformities in any of the lambs delivered. The vaccine in the pregnant ewes induced post-vaccination VN antibody titers against all three serotypes of BTV. Lambs born to the vaccinated ewes also showed a protective level of VN antibody titers against all three serotypes of the virus following passive transfer of maternal antibodies. The levels of VN antibody titers seen in the ewes and lambs were considered sufficient to provide protection against field virus challenge. The results of the current study indicated that inactivated polyvalent bluetongue virus vaccine had no adverse effects on pregnancy and lamb delivery.