Key result
Simulated vaccinate-to-live FMD strategies leave up to ~35% of infected cattle as potential persistent carriers.
Why the study?
The proportion of cattle likely to become FMD carriers and carrier state duration at a herd or population level are incompletely understood, prompting examination of the epidemiologic and economic impacts of a vaccinate-to-live strategy.
A simulated vaccinate-to-live strategy for foot-and-mouth disease in the US suggests that 14-35% of infected surviving cattle could become persistently infected, with production losses being small compared to trade and consumer avoidance losses.
Answers are grounded in this paper and cite their sources.
Vaccinate-to-live FMD strategies may risk persistent cattle infections; simulation evidence leaves open optimal US policy refinements.
Development of a foot-and-mouth disease (FMD) carrier state following FMD virus (FMDV) infection is a well-established phenomenon in cattle. However, the proportion of cattle likely to become carriers and the duration of the carrier state at a herd or population-level are incompletely understood. The objective of this study was to examine the epidemiologic and economic impacts of vaccination-to-live strategy in a disease-free region or country. We developed and simulated scenarios of FMD spread and control in the US livestock population, which included depopulation for a limited period, followed by a vaccinate-to-live strategy with strong biosecurity and movement restrictions. Six scenarios of FMD spread and control were simulated in the InterSpread Plus (ISP) modeling tool. Data on the number of infected and depopulated cattle (by operation types) from ISP model runs were used to estimate the monthly number of infected but not depopulated (potential carrier) cattle after the infection. Using available literature data on the FMD carrier state, we estimated the monthly proportion of carrier cattle (from infected but not depopulated cattle) over time following infection. Among the simulated scenarios, the median (25th, 75th percentile) number of infected cattle ranged from 43,217 (42,819, 55,274) head to 148,907 (75,819, 205,350) head, and the epidemic duration ranged from 20 (11, 30) to 76 (38, 136) days. In general, larger outbreaks occurred when depopulation was carried out through longer periods, and the onset of the vaccination was late ( p > 0.05). The estimated proportion of surviving cattle, which were infected and not depopulated and had the potential to become persistently infected ranged from 14 to 35% of total infected cattle. Production losses in beef and dairy sectors were higher when outbreaks started in multiple states simultaneously, but production losses were small compared to trade losses and consumer avoidance losses. These results can be used to inform the consideration of a vaccinate-to-live strategy for FMD outbreaks and the development of appropriate post-outbreak management strategies. Furthermore, this output will enable a more detailed examination of the epidemiologic and economic implications of allowing convalescent cattle to survive and remain in production chains after FMD outbreaks in FMD-free regions.
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Yadav et al. (2022) studied Foot-and-mouth disease (FMD) (n=1,820,000). Vaccinate-to-live strategy with limited depopulation was evaluated on Proportion of surviving cattle with potential to become persistently infected. In simulated FMD outbreaks using a vaccinate-to-live strategy, the estimated proportion of surviving cattle that were infected and had the potential to become persistently infected ranged from 14% to 35% of total infected cattle.
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