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