Epidemiologic and economic considerations regarding persistently infected cattle during vaccinate-to-live strategies for control of foot-and-mouth disease in FMD-free regions

Abstract

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.

Assessment of a reconfiguration of the InterSpread Plus US national FMD model as a potential tool to analyze a foot-and-mouth disease outbreak on a single large cattle feedlot in the United States

“…Another area to maintain awareness of, is the presence of asymptomatically infected cattle including carriers and neoteric subclinical animals, especially when implementing scenarios that aim to keep cattle through their productive lives ( 42 – 44 ). The model does not explicitly include this population and planning decisions that use these outcomes would need to consider the consequences of carriers in a population of vaccinated or recovered cattle ( 9 ).…”

“…This led the panel to conclude that a large scale depopulation of a feedlot would have serious logistical issues for a rapid response and completion, while maintaining humane treatment of animals and safeguarding the environment after disposal ( 8 ). However, further concerns arise from the occurrence and management of asymptomatic carriers of FMDV that would endure in scenarios that do not include stamping out ( 9 ). Therefore, would it be logical to ask the questions, “How do we apply national level response strategies at the individual feedlot level?” and “Would this make biological sense for a response to a highly infectious pathogen?” When we consider depopulation of all susceptible animals on an infected premise, the depopulated animals can amount to thousands of feedlot cattle resulting in challenges that make it difficult to achieve response objectives.…”

Laboratory testing and on-site storage are successful at mitigating the risk of release of foot-and-mouth disease virus via production of bull semen in the USA

“…Airborne transmission also remains possible, depending on the distance to neighboring barns and other farms. The annual probability of an FMD outbreak in a given facility ( H ), was modeled using an empirical distribution fitted to the data on predicted incidence of FMD outbreaks from five models [ 23 – 27 ]. More details about the estimates used are available in S1 Appendix .…”

Editorial: Promoting compliance with biosecurity in animal production

“…The path forward begins with understanding why management systems and staff are failing to implement effective biosecurity and how to influence those involved to do better. Our understanding of what influences human behavior in the context of animal health and biosecurity has been bolstered in recent decades by transdisciplinary efforts among veterinary scientists and economists, communication specialists, socio-anthropologists, education specialists, and psychologists (1)(2)(3)(4)(5). This understanding can be used to engineer solutions physically, technologically, psychologically, and socially.…”