TRANSMISSION OF PSEUDORABIES VIRUS WITHIN PIG-POPULATIONS IS INDEPENDENT OF THE SIZE OF THE POPULATION

Epidemic models are often used to analyse the transmission of infectio us diseases. These models, however, differ in whether they assume that transmission of a pathogen increases with population size or not. The purpose of this study was to investigate whether the transmission of pseudorabies virus-expressed as the reproduction ratio R-depends on po pulation size. Experimental groups of either ten or 40 vaccinated pigs per group were housed at equal density. We inoculated half of each gr oup, and we estimated the transmission of the virus from the number of contact-infections, using a stochastic Susceptible-Infectious-Recover ed model. We calculated that if the transmission depended on populatio n size, the transmission in the group of 40 pigs would be four times a s high as the transmission in the group of ten pigs. However, the tran smission of the virus did not differ significantly between the groups, and thus we concluded that the transmission was not influenced by the size of the population This finding suggests that control measures sh ould not be aimed at reducing the size of the herd.