Dynamics of pseudorabies virus infections in vaccinated pig populations: a review

This paper reviews our studies on the dynamics of pseudorabies virus (PRV) infections in populations of vaccinated pigs. By using mathematical models, experiments, and field observations, we have been able to quantify PRV transmission by the reproduction ratio R, which is defined as the average number of secondary cases caused by one infectious individual. If R is less than 1, PRV infections will fade out in the pig population and eradication is certain. Under experimental conditions, R of double-vaccinated pigs was estimated at 0.3. In the field, R was estimated at 0.7 among multiple-vaccinated breeding pigs, 3.4 among single vaccinated finishing pigs, and 1.5 among double-vaccinated finishing pigs. So far, no risk factors have been identified that explain the difference between the transmission among double-vaccinated pigs in the field and under experimental conditions. The implications of the transmission characteristics of the different types of pigs for the Dutch PRV eradication campaign are discussed. The structure of the PRV research programme described in this paper, in which knowledge of the interaction of the virus with individual pigs is extrapolated to the interaction of the virus with pig populations, can serve as an example for other research programmes that study infectious diseases.