THE INFLUENCE OF MATERNAL IMMUNITY ON THE TRANSMISSION OF PSEUDORABIES VIRUS AND ON THE EFFECTIVENESS OF VACCINATION

The purpose of this study was to investigate whether maternal immunity could prevent transmission of pseudorabies virus (PRV) among pigs, an d whether it reduced the effectiveness of a single or double vaccinati on with regard to the transmission of PRV. In five experiments, the tr ansmission of PRV, expressed as the reproduction ratio R, was compared in groups of pigs with maternal immunity and in groups of pigs withou t maternal immunity. Transmission of PRV among unvaccinated pigs with maternal immunity (R=0.2) was significantly lower than among pigs with out maternal immunity (R=6.3). Furthermore, maternal immunity in young pigs prevented transmission of PRV as R was significantly below one. In once-vaccinated groups, PRV spread extensively among pigs with mate rnal immunity (R=23), but did not spread extensively among pigs withou t maternal immunity (R=0.6). In twice-vaccinated groups, transmission of PRV among pigs with material immunity (R=0.6) did not differ signif icantly from the transmission of PRV among pigs without maternal immun ity (R=0.3). Thus, a single vaccination of pigs with PRV strain 783 at 10 weeks of age, when they still possessed maternal immunity, seemed not sufficient to prevent transmission of PRV. Virus transmission coul d be reduced however, if maternally immune pigs were vaccinated twice at 10 and 14 weeks of age. (C) 1997 Elsevier Science Ltd.