Mucosal disease: origins and outcome in cattle

Volker Moennig

Mucosal disease is a fatal cattle disease which exclusively affects persistently infected animals. They were transplacentally infected with a non-cytopathic (ncp) BVD virus during gestation while their immune system was not yet fully developed. Hence, they accepted the virus as ‘self’, they did not develop antibodies against the virus and they are immunotolerant against this particular BVD virus. Their survival time ranges from a few days to many years. Throughout their lives they produce and shed ncp BVD virus in huge quantities.

When the ncp BVD virus in persistently-infected cattle mutates to a cytopathic (cp) one or when these animals are accidentally superinfected with an antigenetically identical or very similar cp virus, mucosal disease is triggered. Due to the high mutation rate of RNA viruses like BVD virus, such mutations of ncp viruses to cp variants may occur occasionally and the likelihood of a superinfection of persistenty infected animals is quite high. Since persistently infected animals are immunotolerant against “their” endogenous ncp BVD virus, the cp virus mutants can kill large amounts of cells without interference by the animal’s immune system. Especially the gastro-intestinal tract will display huge lesions which lead to the dramatic clinical picture of bloody diarrhoea. There is no cure and mucosal disease is always fatal.