Bovine herpesvirus (BoHV-1) abortion in dairy cattle
Siobhan O’Sullivan, Rebecca Egan
Animal Health Laboratory, University of Guelph, Guelph, ON.
AHL Newsletter 2022;26(3):12.
Multiple aborted bovine fetuses were received from a dairy farm with a history of over 15 abortions occurring over a one month period. On postmortem examination, aborted fetuses were estimated to be approximately 6 months gestation, and there were no specific gross diagnostic lesions. Histopathology revealed multifocal acute hepatic necrosis in all fetuses (Fig. 1), and small foci of necrosis in the lung and adrenal glands of some fetuses. Fetal tissues were consistently positive for Bovine herpesvirus-1 (BoHV-1) by PCR with cycle threshold (Ct) values between 22 and 25. Leptospira sp. and Neospora caninum were not detected by PCR. The presence of typical microscopic lesions of infection combined with PCR detection of BoHV-1 in all fetuses confirmed this agent as the cause of abortions, despite this herd having a history of vaccination.
This was one of four total cases of confirmed BoHV-1 abortion submitted to the AHL in 2021-2022. Cases generally represent localized outbreaks of multiple aborted fetuses, often between 5-8 months of gestation. The characteristic histologic lesions of BoHV-1 infections are foci of necrosis in multiple organs, especially in the liver and often with intranuclear viral inclusion bodies in adjacent cells, as well as necrotizing vasculitis in the placenta. Gross lesions are not always evident, but can include white-tan foci of hepatic and/or pulmonary necrosis and renal hemorrhage.
In addition to abortion, BoHV-1 is also the causative agent of other recognized reproductive and respiratory production diseases, including infectious bovine rhinotracheitis (IBR) and infectious pustular vulvovaginitis/balanoposthitis. Viral latency and recrudescence following periods of stress are features of infection with BoHV-1, allowing infected but asymptomatic individuals to act as potential reservoirs of infection for other animals. The virus is transmitted between bovines by contact with respiratory, ocular, or vaginal discharges, and semen. Vaccination protocols are generally effective for prevention and control; however, vaccination of ill, stressed, immunocompromised animals, or missed or improperly timed doses, can result in breakthrough infections. AHL
Figure 1. Bovine fetus, liver. Two foci of hepatic necrosis (arrows) with loss of hepatocytes, loss of differential staining, and accumulated cell debris. H&E stain.
References
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