Modelling environmentally mediated spread of livestock-associated methicillin-resistant Staphylococcus aureus in a pig herd

Abstract

Infectious disease models are a useful tool to support within-herd disease control strategies. This study presents a stochastic compartment model with environmentally mediated transmission to represent the spread of livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) in a farrow-to-finish pig herd. The aims of the study were to (1) construct a model of the spread of LA-MRSA that included spread of LA-MRSA through the environment; (2) parameterise the model to fit previously published observational data in order to obtain realistic LA-MRSA transmission rates; (3) and to investigate how changes in the mixing of animals in the farrowing and finishing units may affect the prevalence of LA-MRSA in a herd. The results showed that indirect transmission allowed LA-MRSA to persist in the herd without the assumption of persistently shedding individuals. Reducing the mixing of pigs upon entry to the finishing unit was also shown to lower the LA-MRSA prevalence in the unit if the initial LA-MRSA level in the unit was low, but at high prevalence, no effect of mixing was identified. In the farrowing unit, changing the proportion of piglets that were cross-fostered did not affect the within-herd LA-MRSA prevalence. The study demonstrates that there are several important knowledge gaps regarding the shedding and transmission of LA-MRSA in different animal age groups and further experimental studies are needed. This work also provides a new, robust and flexible model framework for the investigation of control and mitigation strategies for LA-MRSA and other infections in a pig herd.