Impacts of constrained culling and vaccination on control of foot and mouth disease in near-endemic settings: A pair approximation model

Abstract

Many countries have eliminated foot and mouth disease (FMD), but outbreaks remain common in other countries. Rapid development of international trade in animals and animal products has increased the risk of disease introduction to FMD-free countries. Most mathematical models of FMD are tailored to settings that are normally disease-free, and few models have explored the impact of constrained control measures in a 'near-endemic' spatially distributed host population subject to frequent FMD re-introductions from nearby endemic wild populations, as characterizes many low-income, resource-limited countries. Here we construct a pair approximation model of FMD and investigate the impact of constraints on total vaccine supply for prophylactic and ring vaccination, and constraints on culling rates and cumulative culls. We incorporate natural immunity waning and vaccine waning, which are important factors for near-endemic populations. We find that, when vaccine supply is sufficiently limited, the optimal approach for minimizing cumulative infections combines rapid deployment of ring vaccination during outbreaks with a contrasting approach of careful rationing of prophylactic vaccination over the year, such that supplies last as long as possible (and with the bulk of vaccines dedicated toward prophylactic vaccination). Thus, for optimal long-term control of the disease by vaccination in near-endemic settings when vaccine supply is limited, it is best to spread out prophylactic vaccination as much as possible. Regardless of culling constraints, the optimal culling strategy is rapid identification of infected premises and their immediate contacts at the initial stages of an outbreak, and rapid culling of infected premises and farms deemed to be at high risk of infection (as opposed to culling only the infected farms). Optimal culling strategies are similar when social impact is the outcome of interest. We conclude that more FMD transmission models should be developed that are specific to the challenges of FMD control in near-endemic, low-income countries.

Lyapunov Stability Analysis of a Delayed Foot-and-Mouth Disease Model with Animal Vaccination

“…Since the 2001 FMD outbreak in UK, several mathematical models have been proposed to study the transmission and control of FMD (see, e.g., [6,[8][9][10][11][12][13][14][15][16][17][18][19][20][21]). Dexter [8] utilised stochastic epidemic models to explore the dynamics of FMD among feral pigs in the Australian semiarid rangelands.…”

Modeling the Effects of Multiple Intervention Strategies on Controlling Foot-and-Mouth Disease

“…The causative agent of the disease is a small icosahedral nonenveloped RNA virus classified within the Aphthovirus genus, as a member of the Picornaviridae [ 2 ]. The virus is airborne and can also be transmitted through physical contact with infected animals' expired air, saliva, milk, urine, semen, animal feed and bedding, and so forth [ 3 ]. Direct or indirect contact with FMD-infected animals can result in susceptible animals becoming diseased or subclinically infected [ 2 ].…”

“…Conventional control measures of the disease include movement restriction—for example, through construction of “veterinary boundaries”—that is, cordon fences erected to divide a country into multiple subregions to restrict the movement of animals across the borders; educational awareness; quarantine; vaccination and culling of detected infected animals [ 3 ]. Practising import regulations can be essential to prevent FMDV from being introduced from endemic regions in infected animals or contaminated foodstuffs fed to animals [ 4 ].…”

“…Since the 2001 FMD outbreak in the United Kingdom mathematical modeling of FMD has been an interesting topic for a number of researchers; see, for example, [ 3 , 8 – 11 ]. Tildesley et al [ 8 ] proposed a probabilistic FMD transmission model to explore an optimal deployment strategy of limited reactive ring vaccination of cattle in a single epidemic outbreak.…”

“…Results from their study highlighted a number of areas that warrant further study and also emphasized the impact of time-optimal control on controlling the generation of new infections in resource-limited settings. More recently, Ringa and Bauch [ 3 ] developed an SEIRVC, Susceptible-Exposed-Infectious-Removed-Vaccinated-Culled, pair-approximation model of FMD transmission in a near-endemic population. Their work suggested that the optimal long-term control of FMD by vaccination in near-endemic settings can be achieved by rolling out a prophylactic vaccine as much as possible, especially if resources are limited.…”