Antigenic Relationship of Different Porcine Rotavirus Isolates and the Identification of a New Porcine Strain
The problem. Currently, only one strain of porcine rotavlrus has been reported. This strain, designated OSU, has been attenuated and is currently available as a federally licensed, live oral vaccine for pigs. This study is concerned with the antigenic relationship of the OSU vaccine strain to four virulent porcine rotavirus isolates as measured by the vaccine's serologic cross-reactivity in vitro. Procedures. Four virulent isolates of porcine rotavirus were adapted to tissue culture. Purified viral antigens were prepared from low passage tissue culture adapted virus fluids. Upon purification both complete and single-shelled rotavirus particles were observed by electron microscopy. Furthermore, all virus bulks were identified as rotavirus by positive fluorescence obtained by immunofluorescent staining of inoculated cell cultures. The antigens were used to produce high titer hyper immune sera in guinea pigs. These sera were used in appropriate serological studies in vitro to determine the amount of antigenic cross-reactivity between the different isolates. Antigenic cross-reactivity was measured by the amount of virus neutralized by homologous and heterologous sera. Neutralizing indices were calculated and all virus isolates compared. Findings. Two distinct serotypic groups were observed; the original OSU strain and a new straln of porcine rotavirus identified as the Iowa strain. The new strain was found to be significantly different from the OSU strain as measured by its lack of serologic cross-neutrallzation. Conclusions. The results indicate a minor antigenic similarity between the two strains as found in low dilutions of the hyperimmune sera. Nevertheless, there was an absence of any major antigenic similarity between the two stralns. Therefore this lack of any major antigenic crossneutralization between the two strains suggests the Iowa strain is unique and can be classified as a new strain of porcine rotavirus.