Key result
Stochastic compartmental modeling of cattle herds suggests that repeated introduction of foot and mouth disease virus from outside the herd is required for long-term viral persistence.
Why the study?
Smallholder livestock keepers experience significant losses due to foot and mouth disease, but the dynamics and mechanisms underlying persistence at the herd-level and beyond remain poorly understood.
Mathematical modeling suggests that Foot and Mouth Disease cannot persist indefinitely in an isolated cattle herd without repeated viral introduction, even if a carrier state exists.
Supports focusing FMD control on preventing external introductions; leaves open validation in diverse field settings.
Foot and mouth disease (FMD) burden disproportionally affects Africa where it is considered endemic. Smallholder livestock keepers experience significant losses due to disease, but the dynamics and mechanisms underlying persistence at the herd-level and beyond remain poorly understood. We address this knowledge gap using stochastic, compartmental modelling to explore FMD virus (FMDV) persistence, outbreak dynamics and disease burden in individual cattle herds within an endemic setting. Our analysis suggests repeated introduction of virus from outside the herd is required for long-term viral persistence, irrespective of carrier presence. Risk of new disease exposures resulting in significant secondary outbreaks is reduced by the presence of immune individuals giving rise to a period of reduced risk, the predicted duration of which suggests that multiple strains of FMDV are responsible for observed yearly herd-level outbreaks. Our analysis suggests management of population turnover could potentially reduce disease burden and deliberate infection of cattle, practiced by local livestock keepers in parts of Africa, has little effect on the duration of the reduced risk period but increases disease burden. This work suggests that FMD control should be implemented beyond individual herds but, in the interim, herd management may be used to reduced FMD impact to livestock keepers.
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McLachlan et al. (2019) studied Foot and mouth disease (n=70). Carrier state inclusion and herd management practices vs. Model without carriers was evaluated on Mean duration of simulated outbreaks (without carrier state, in years) (95% CI 0.082-0.084). Stochastic compartmental modeling of cattle herds suggests that repeated introduction of foot and mouth disease virus from outside the herd is required for long-term viral persistence.