Experimental louping-ill virus infection of cattle.

The response of six calves to subcutaneous inoculation with louping-ill virus was studied. All developed viraemia of low intensity which lasted two to four days followed by the appearance of haemagglutination inhibiting serum antibody. IgM was the predominant class of antibody until day 14. Only one calf developed clinical signs; following a brief period of incoordination on day 7 it became recumbent and was killed on day 12. Severe meningoencephalitis was detected in this calf and mild changes were observed in one of the five survivors which were killed on day 14 or 20. These findings are discussed in relation to the epidemiology of louping-ill and the diagnosis of the disease in cattle.