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Two bovine rotaviruses, C3-160 and 17/4, which multiplied in calves without inducing disease, were studied for their ability to protect against disease caused by a virulent rotavirus, CP-1. Rotavirus 17/4 and the virulent virus CP-1 cross-neutralized poorly and, on the basis of 20-fold differences in neutralization titres, belonged to different serotypes. Rotaviruses C3-160 and CP-1 were more closely related: neutralization of the CP-1 virus by C3-160 antisera was within 20-fold of the homologous titre although neutralization of the C3-160 virus by CP-1 antisera was not. Nine gnotobiotic calves infected with either C3-160 or 17/4, had rotavirus antibody in their faeces and/or serum 21 days after oral inoculation as detected by indirect immunofluorescence and IgG, IgM and/or IgA antibodies by ELISA. As expected from the antigenic relationships between the viruses, the sera and faeces from the four calves infected with C3-160 contained moderate levels of neutralizing antibody to the virulent virus CP-1 and the sera and most of the faeces from the five calves infected with 17/4 contained undetectable or low levels. When challenged with CP-1 on day 21, four age-matched controls developed disease whereas all of four calves previously infected with C3-160 and four of five calves previously infected with 17/4 were protected from disease. It was concluded that avirulent rotavirus infection provided protection against disease caused by a virulent rotavirus even when one of the avirulent viruses was poorly related to the virulent virus by neutralization. Mechanisms other than neutralizing antibody appeared to be important in protection.
Bridger et al. (Tue,) studied this question.