Teratogenic bluetongue and related orbivirus infections in pregnant ruminant livestock: timing and pathogen genetics are critical.

•Congenital infections with viruses in several families can result in teratogenic defects in domestic animals.•Strains of blue tongue virus (BTV) modified by growth in embryonated eggs or cell culture are highly teratogenic.•Congenital BTV infection can result in central nervous system teratogenesis, but typically not arthrogryposis.•BTV-induced caveating brain lesions reflect virus-mediated destruction of neuronal and glial cells precursors.•The severity of BTV-induced fetal teratogenesis reflects gestational age of the fetus at infection.