Virus-induced congenital malformations in cattle

Congenital malformations are accepted to occur sporadically however, if the incidence increases on a farm, veterinary investigation is often sought to determine the aetiology.

There is a wide spectrum of bovine congenital syndromes and diagnosis is extremely challenging, often based only on clinical findings and gross lesions. While virus-induced congenital malformations (VICMs) may be diagnosed by laboratory analysis, being antibody- or antigen-positive does not necessarily imply that the virus caused the malformation.

Foetal infection with BVDV is reported to be associated with various congenital malformations, which particularly affect the brain (cerebellar hypoplasia is most frequently reported), followed by the musculoskeletal system.

The teratogenic effects of BVDV infection of the susceptible dam have been reported to occur following infection at between 79 and 150 days of gestation. Reportedly affecting, primarily, the CNS due to it’s vulnerability during this time period. The CNS pathology is thought to result from both direct cellular damage and the inflammatory response to viral infection.

BVDV destroys immature neuronal and neuroglial cells causing failure of their migration, and induces destruction of brain parenchyma. This leads to the formation of cavitating lesions in the cerebrum e.g. hydraencephaly and porencephaly. In the cerebellum, Purkinje cells are also affected and inflammatory vascular lesions are responsible for the development of cavitating lesions.

Further congenital malformations associated with BVDV include ocular lesions (commonly associated with cerebellar hypoplasia), thymic and lung hypoplasia, renal dysplasia and alterations of bones and hair coat. These lesions are reported to occur either as single entities or associated with CNS or ocular lesions.

In conclusion, no gross lesions are pathognomonic for VICMs and suspicions should ideally be confirmed by the demonstration of lesions known to be associated with viral infection, supported by demonstration of congenital antibodies or virus. The authors recommend that advice is sought from experts in teratology and genetic disorders, and that the neonate is submitted for laboratory examination.