Respiratory disease caused by bovine viral diarrhoea virus

The biological characteristics of two bovine vit-al diarrhoea virus (BVDV) isolates belonging to Type 1 were studied in an experiment involving artifi cial infection of animals, with special regard to the clinical signs caused by the virus in calves, the appearance of seropositivity and the distribut ion of the virus in several organs. The viruses represent a new genetic clu ster and were isolated in Southern Africa from cattle showing respiratory s ymptoms. After a latency period of 4-7 days, all of the 8 infected calves started to show clinical signs the most typical of which mere nasal and ocular discha rge, coughing, laboured breathing and erosions in the oral mucosa The two: in-contact control animals also contacted the disease which indicates the p otential of the virus to spread within herds. There was no difference in th e severity of symptoms between the intravenously and intranasally infected animals. Antibodies detectable by ELISA appeared in all calves except in-contact con trols. Viral nucleic acid was detected with RT-PCR in nasal swab, lymphocyt es, nasal mucosa, lungs, tonsils and bone marrow, in a total of 16 samples. The experimental results support the assumption that the two BVDV isolates are adapted to the respiratory organs and are able to elicit symptoms of m oderate severity in immunocompetent seronegative calves.