Evidence of brain dysplasia associated with transplacental transmission of the two current European strains of bluetongue virus serotype 3 in bovine fetuses

Abstract Bluetongue virus serotype 3 (BTV‐3) recently re‐emerged in northern Europe, raising concerns about its pathogenicity and economic impact on the livestock industry. While transplacental transmission has been documented for specific BTV serotypes, congenital malformations were only reported after transplacental BTV‐8 infection. Here, we report three cases of congenital brain malformations in bovine fetuses and newborn calves, in which BTV‐3 could be detected in both spleen and midbrain tissues via quantitative reverse transcription‐polymerase chain reaction. These findings demonstrate a tropism of BTV‐3 for the central nervous system, where it causes non‐development of the cerebrum, and persists in the spleen and central nervous system until at least 10 days after birth. These findings raise the question of whether (i) seropositive offspring can be persistently infected and serve as a potential reservoir for BTV‐3, and (ii) if current vaccines are effective in preventing vertical transmission.