Physicochemical characterization of porcine pararotavirus and detection of virus and viral antibodies using cell culture immunofluorescence

Abstract

A cell culture immunofluorescence (CCIF) assay was optimized for detection of porcine pararotavirus (group C rotavirus) in intestinal contents. The greatest vital infectivity was observed when MA104 cells (5 days after subculturing) were rinsed and refed in serum-free medium before inoculation, pancreatin was added to the inocula, and the inocula were centrifuged onto the cells. Gentamicin treatment of pararotavirus samples to reduce bacterial contamination also reduced the vital infectivity of these samples for MA104 cells. An indirect CCIF assay was used to determine the prevalence of pararotavirus and rotavirus antibodies in pig sera. In pigs from four herds, pararotavirus antibodies were detected in 100% (68 of 68) of adults and 59% (24 of 41) of weanling pigs, while 86% (24 of 28) of nursing pigs from 12 herds had pararotavirus antibodies. The physicochemical properties of pararotavirus were examined and compared with those of group A rotaviruses by using the CCIF assay to quantitate in vitro changes in viral infectivity. Pararotavirus was inactivated (≥ 99% reduction in titer) by heating to 56°C for 30 min, was slightly labile at pH 3 (16 to 34% reduction in titer), and was stable at pH 5 (0 to 17% reduction in titer) and in ether (3 to 19% reduction in titer). One group A rotavirus (Gottfried strain) was stable at 56°C (0% reduction in titer), whereas the OSU strain of group A rotavirus was inactivated at this temperature (99% reduction in titer).