Quantification of within- and between-pen transmission of Foot-and-Mouth Disease Virus in pigs

Quantified transmission parameters of Foot-and-Mouth Disease Virus (FMDV) are needed for epidemic models used for control and surveillance. In this study, we quantified the within- and between-pen transmission of FMDV in groups of pigs by estimating the daily transmission rate beta, i.e. the number of secondary infections caused by one infectious pig during one day, using an SIR (susceptible-infectious-removed) model. Within-pen transmission was studied in four groups of ten pigs in which 5 infected and 5 susceptible pigs had direct contact; between-pen transmission was studied in one group of ten pigs in which 5 infected and 5 susceptible pigs had indirect contact. Daily results of virus isolation of oropharyngeal fluid were used to quantify the transmission rate beta, using Generalised Linear Modelling (GLM) and a maximum likelihood method. In addition, we estimated the expected time to infection of the first pig within a pen T-W and in the indirect-contact pen T-b. The between-pen transmission rate beta(b) was estimated to be 0.59 (0.083-4.18) per day, which was significantly lower than the within- pen transmission rate beta(W) of 6.14 (3.75-10.06). T-W was 1.6 h, and T-b was 16 h. Our results show that the transmission rate is influenced by contact structure between pigs.