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.

The field effectiveness of routine and emergency vaccination with an inactivated vaccine against foot and mouth disease.

High potency, inactivated foot and mouth disease (FMD) vaccines may be used in non endemic countries for emergency vaccination during outbreaks in order to prevent virus spread. In endemic countries either standard or high potency vaccines are used for routine vaccination. Despite their wide use there is a shortage of data on the field effectiveness of inactivated FMD vaccines. Epidemics of FMD caused by viruses of serotype O occur frequently in Israel, where a high potency (≥6PD(50)) vaccine is used for both routine and emergency vaccination. We investigated an outbreak of FMD caused by a virus of serotype O, which took place during 2011 in a feedlot and an adjacent dairy herd. Post outbreak testing of antibodies against non-structural protein demonstrated that infection occurred in 96% of the calves that received two doses of vaccine at least three months prior to the outbreak and more than 50% showed clinical signs consistent with FMD. Replacement heifers that had been vaccinated 3-5 times with the last vaccination administered 7 months prior to the outbreak were all infected and 18% showed clinical signs. Testing of cattle sera of the same vaccination status as the affected cattle demonstrated low neutralizing antibody (NA) titers against the field virus strain and an r(1) value of 0.37 compared to the vaccine strain. In contrast, cattle vaccinated only once but up to two weeks before the outbreak, were almost all protected from clinical disease and to a lesser extent, protected from FMD virus infection, despite low NA titers. We conclude that emergency vaccination was highly effective due to a mechanism not associated with NA, whereas routine vaccination with the same vaccine formulation provided only limited protection due to poor longevity of the elicited immunity and low matching with the field strain (despite an r(1) higher than 0.3).