Incidence of group A and atypical rotaviruses in Brazilian pig herds.

The incidence of rotaviruses as a gastroenteritis causal agent in piglets was studied in 19 pig herds of Sao Paulo State, Brazil, during 1985. From 302 diarrhoea samples collected during January (summer), 65 were positive for rotavirus when analysed by enzyme-linked immunosorbent assay (ELISA) and polyacrylamide gel electrophoresis (PAGE). Sixty-two of these samples belonged to the classical group A rotavirus, three to atypical rotaviruses (ELISA negative and probably group B) and one elicited a mixed electropherotype of group A and atypical rotavirus and was ELISA positive. Atypical viruses appear to be very fragile and were rapidly degraded upon storage of samples at -20 degrees C. Three herds where atypical rotaviruses were present in January were sampled again in August (winter). Nine atypical isolates out of a total 21 positive samples (assayed by electron microscopy and PAGE) were detected again in two of them.