No abstract

A bovine calici-like virus and astrovirus, present in the same fecal sample from an outbreak of diarrhea, were separated from each other by calf passage. The calici-like virus (Newbury agent SRV-1) caused anorexia, diarrhea, and xylose malabsorption in gnotobiotic calves aged 17 to 60 days, whereas the bovine astrovirus was nonpathogenic in similar calves. The calici-like virus was shown to be antigenically distinct from a previously described isolate (Newbury agent SRV-2) by two-way cross-protection experiments in calves; calves immune to homologous challenge became clinically ill and excreted virus when challenged with the heterologous virus.

SUMMARYThe antigenic relationships between three bovine rotaviruses, UK, CP-1 and PP-1, and a porcine rotavirus were investigated; their pathogenicity for piglets was also assessed. After propagation and cloning in cell culture, the four viruses were used to produce convalescent and hyperimmune antisera in gnotobiotic animals. For the UK and PP-1 viruses, reciprocal virus neutralization tests gave ratios of homologous to heterologous titres in the range 57 to > 2300. Taking a 20-fold difference in titre to be the criterion of heterogeneity, these two viruses could be regarded as separate serotypes. The third bovine virus, CP-1, was identical to PP-1 in reciprocal neutralization tests but gave a one-way cross-reaction with UK convalescent sera, i.e. it appeared to be intermediate between the two serotypes. UK and CP-1 differed antigenically from the porcine virus as shown by .homologous:heterologous neutralization titre ratios of 30 to 12 600. The bovine virus, PP-1, however, had a closer relationship with the porcine virus, the homologous : heterologous ratios ranging from 4 to 110. Oral inoculation of piglets with the bovine viruses revealed differences in their pathogenicity. Isolates UK and CP-1 caused no clinical disease and could not be passaged. However, on the first and second passages in pigs, the bovine virus PP-1 and the porcine virus produced clinical disease, excretion of virus in the faeces and seroconversion. The results suggest that PP-1 may be a natural hybrid between a bovine and a porcine rotavirus.

Bovine colostrum with rotavirus-neutralizing activity was fed for 10 days to two groups of piglets, one of which was inoculated intranasally with a rotavirus of porcine origin. A third group, which did not receive colostrum, was also inoculated with the virus, and these piglets developed diarrhea, excreted rotavirus in the feces, and died 6 days after infection. In contrast, the infected piglets fed with bovine colostrum remained healthy, although they developed antibody to rotavirus. Twenty-seven days after the primary inoculation, piglets in the colostrum-fed groups were inoculated intranasally with virus. Those in the previously unexposed group became clinically ill and excreted rotavirus, whereas those which had experienced a previous subclinical infection (the colostrum-fed, virus-inoculated group) remained healthy. It was concluded that bovine colostrum protected piglets from the clinical effects of a porcine rotavirus and that these animals developed an immunity which prevented subsequent disease.