Characterization of group C rotaviruses associated with diarrhea outbreaksin feeder pigs

Feces and serum specimens were collected from three farms in Michigan on wh ich similar to 50-lb (8- to 9-week-old) pigs experienced diarrhea just afte r placement into all-in-all-out finishing barns. The clinical signs (profus e watery diarrhea lasting about 2 weeks and no, vomiting) were similar on a ll farms, and the morbidity rate was high (ranging from 60 to 80%) but with out mortality. Eleven diarrheic fecal samples from the farms,were tested fo r group A and C rotaviruses by immune electron microscopy (IEM) and various assays, IEM indicated that the Fecal samples reacted only with antiserum a gainst group C rotaviruses, and polyacrylamide gel electrophoresis indicate d that the samples had characteristic genomic electropherotypes for group C rotavirus. Group C rotavirus was detected by cell culture immunofluorescen ce (CCIF) tests in nine fecal samples, but no group A rotavirus was detecte d by enzyme-linked immunosorbent assay or CCIF, By reverse transcription (R T)-PCR, all 11 fecal samples H-ere positive for group C rotaviruses, with o nly 2 samples positive for group A rotaviruses. However, a second amplifica tion of RT-PCR products using nested primers detected group A rotaviruses i n all samples. Analysis of nucleotide and deduced amino acid sequences of t he RT-PCR product (partial-length VP7) of the group C rotavirus shelved 87. 2 to 91% nucleotide identity and 92.6 to 95.9% amino acid identity among tw o strong samples from the different farms and the Cowden strain of porcine group C rotavirus. All nine convalescent-phase serum samples tested had neu tralizing antibodies to the Cowden strain, and the majority of them had neu tralizing antibody against group A rotaviruses (OSU or/and Gottfried strain s) by fluorescent focus neutralization tests, Although group C rotaviruses hare been reported as a cause of sporadic diarrhea in suckling or weanling pigs, to our knowledge, this is the first report of epidemic diarrhea outbr eaks associated with group C rotavirus in older pigs.