Congenital cerebral and cerebellar anomalies in relation to bovine viral diarrhoea virus and Akabane virus in newborn calves

Congenital malformations occur sporadically in cattle; however, congenital structural and functional disorders of the nervous system are rather common in ruminants. Among the numerous causes of congenital nervous system defects, infectious agents are highlighted in this paper. Virus-induced congenital malformations are well known, among which those caused by bovine viral diarrhoea virus (BVDV), Akabane virus (AKAV), Schmallenberg virus (SBV), Bluetongue virus (BTV), and Aino virus (AV) are the most studied. In this study, we specify and categorise macroscopic and histopathological lesions in the brain of 42 newborn calves suffering from severe neurologic signs and diagnosed with BVDV and AKAV infection. Following a complete necropsy, specimens were collected from the brains to track the presence of BVDV, AKAV and SBV utilising reverse transcription polymerase chain reaction. Of the 42 examined calves, 21 were BVDV positive and 6 were AKAV positive, while 15 brains were negative for the studied agents. Regardless of the aetiology, cerebellar hypoplasia, hydranencephaly, hydrocephalus, porencephaly, and microencephaly were detected. Cerebellar hypoplasia was the most common lesion seen in both BVDV-positive and AKAV-positive cases. Virus-induced necrosis of the germinative cells of the external granular layer of cerebellum, as well as vascular damages, are believed to be the underlying causes of cerebellar hypoplasia. BVDV was the most important aetiological agent of such cases in this study.