Risk factors for foot and mouth disease outbreaks in grazing beef cattle herds

Foot and mouth disease (FMD) is considered one of the most important diseases of cattle. Recurrence of FMD outbreaks in Israel is common, even though routine vaccination of livestock is mandatory and control measures are applied during the outbreaks. Grazing beef herds are occasionally involved in these outbreaks and play an important role in disseminating the disease, due to the large efflux of animals from these herds to feedlots. Nevertheless, the risk factors for the occurrence of FMD among these herds have never been investigated. In 2011, Israel faced a large scale outbreak of serotype O FMD virus, which strongly affected beef cattle. We conducted a case-control study of 44 beef cattle herds grazing in the Golan Heights in order to determine the risk factors for FMDV infection. Data were analyzed using a generalized estimation equation (GEE) with a logit link function. Multivariable analysis was conducted for factors with p-value lower than 0.1 in the univariable analysis. The presence of calves under 6 months of age was found as a significant risk factor for FMDV infection in the univariable analysis (odds ratio (OR)=5.95, confidence intervals of 95% (CI95%)=1.59-22.29, p=0.008). This was also the only variable that remained statistically significant in the multivariable analysis. Herds in which more than 6 months between vaccination of adults and exposure had elapsed were in higher risk, albeit not statistically significant, for the occurrence of FMDV infection (OR=3.29, CI95%=0.83-12.99, p=0.089). The higher probability of infection in herds, which included young calves may be a result of their higher susceptibility due to administration of only one or no vaccine prior to the outbreak. The results of the study thus support increasing the frequency of vaccination of both cows and calves in grazing beef herds. Intensifying surveillance where young calves are abundant may also prove efficient for early detection of infected herds and for mitigating outbreaks of FMDV.