Evidence of serologic diversity within group C rotaviruses

The Cowden strain of porcine group C rotavirus and the Shintoku strain of bovine group C rotavirus were classified as different serotypes by two-way cross-neutralization tests. Two neutralization patterns against the Cowden and Shintoku strains were observed when hyperimmune or convalescent-phase antisera to three noncultivatable porcine group C rotaviruses and a human group C rotavirus were used in one-way cross-neutralization tests. Antisera to two porcine group C rotaviruses and the human group C rotavirus neutralized the Cowden strain at high titers but did not neutralize the Shintoku strain, suggesting that these three strains are serotypically related to the Cowden strain. The remaining antisera to a porcine group C rotavirus (HF strain) reacted with the Cowden and Shintoku group C rotaviruses in cell culture immunofluorescence tests but did not neutralize either virus in one-way cross-neutralization, suggesting that the HF strain belongs to a third serotype. However, confirmation of these findings requires additional analysis by two-way cross-neutralization. Our findings support the existence of at least two distinct serotypes of group C rotaviruses, and possibly a third, among animals and humans. The serotypic similarity observed between the Cowden strain and a human group C rotavirus suggests that the cultivatable Cowden strain and antiserum to this virus may provide important reagents for the diagnosis of group C rotaviruses in humans.