Prolonged nasal shedding and viraemia of cytopathogenic bovine virus diarrhoea virus in experimental late-onset mucosal disease

A calf persistently infected with bovine virus diarrhoea virus (BVDV) was s uper-infected with a heterologous BVDV strain, C874, which contained non-cy topathogenic and cytopathogenic viruses, High titres of cytopathogenic BVDV were recovered in the three to four weeks after the challenge. Thereafter low titres of cytopathogenic virus were recovered repeatedly from the blood and the nose, with the titres in nasal secretions increasing in the four w eeks before the onset of clinical signs. Neutralising antibodies against th e challenge cytopathic virus (C874cp) were first detected 21 days after the super-infection, but these antibodies failed to neutralise the persisting noncytopathogenic and cytopathogenic viruses isolated from the animal durin g the course of the infection. Serum collected from 105 days after the supe r-infection neutralised the cytopathogenic viruses isolated on day 105 and postmortem, These data indicate that unaltered wild-type C874cp was not dir ectly responsible for the late-onset mucosal disease.