Hemagglutination with Porcine Reproductive and Respiratory SyndromeVirus.

Porcine reproductive and respiratory syndrome (PRRS) virus grown on MARC-145 cell cultures was tested for hemagglutination (HA) with erythrocytes from a variety of species at 4°C, room temperature and 37°C. HA was observed at all temperatures with mouse erythrocytes but not with cattle, sheep, goat, horse, swine, guinea pig, mongolian gerbil, goose and chicken erythrocytes. The HA activity was enhanced by treatment of virus materials with Tween 80 followed by treatment with ether. The HA titer and HA pattern of virus materials treated with Tween 80 and ether (TE) were 4- to 8-fold higher and more clear than those of the virus materials without TE treatment. The optimum conditions consisted in pretreatment of virus material with Tween 80 at a final concentration of 0.06-0.125% (v/v) for 15-60 min followed by treatment with ether at a concentration of 50% (v/v) for 5-15 min in ice bath with continuous shaking. The curve of active virus production in intra- and extracellular virus samples resembled that of HA production although it rose somewhat earlier in intracellular virus samples. The HA reaction was inhibited by specific antiserum. HI antibody titers of individual pig sera showed a significant positive correlation with their neutralizing antibody titers.