Variation in virulence of bovine rotaviruses

Abstract

SUMMARY: Forty-six gnotobiotic calves aged less than 16 days or 42–116 days were infected with three strains of bovine rotavirus designated C3–160, CP-1 and PP-1. Each virus was passaged and cloned in cell culture (cloned viruses) but CP-1 and PP-1 Were also used before culture (faecal viruses).Infection of calves aged less than 16 days with faecal or cloned CP-1 caused disease whereas cloned C3–160 and faecal or cloned PP-1 caused subclinical infections. The clinical signs of disease were change in faecal colour to pale yellow or cream, increase of 2- to 7-fold in the volume of faecal output and, usually, anorexia. With the virulent CP-1 virus and the avirulent C3–160, similar amounts of virus were excreted in the faeces for 4–6 days.Infection of calves aged 56–116days with faecal CP-1 produced disease of similar severity to that seen in calves aged 7–10 days infected with the same virus. No differences in clinical signs, virus excretion or levels of convalescent antibody were seen between the two groups. With cloned CP-1, 5 of 8 older calves developed disease but 3 showed only mild signs of infection.It was concluded that two strains of rotavirus caused sub-clinical infections in young calves while a third was virulent in calves up to at least 116 days of age.