Bovine herpesviral meningoencephalitis: large case study and literature review

Bovine herpesviral meningoencephalitis (BHM) is an infectious disease of cattle caused by bovine alphaherpesvirus 1 (BoAHV1; Orthoherpesviridae, Varicellovirus bovinealpha1) or 5 (BoAHV5; Orthoherpesviridae, Varicellovirus bovinealpha5). Cases are frequent in South America, but the disease is sporadic in other countries. Infection typically leads to fatal necrotizing meningoencephalitis that most often affects calves <1-y-old and yearlings under stressful situations, including weaning, large concentrations of animals, transport, and introduction of cattle from other locations into a herd. Clinical disease lasts from 1-10 d and often leads to typical gross and histologic lesions that are more prominent in the frontal lobes of the brain. This particular neuroanatomic distribution of lesions results from retrograde viral infection from the nasal mucosa along the olfactory nerves and bulbs with subsequent spread to the rostral cerebrum. Because of its particular geographic distribution, many aspects of BHM are still poorly documented in the English language veterinary literature, and thus a comprehensive review of the disease is warranted. Here we review the main aspects of BHM, including its historical timeline, etiology, pathogenesis, epidemiology, clinical and pathologic findings, diagnosis, and control and prophylaxis.