Mathematical model of the 2010 foot-and-mouth disease epidemic in Japan and evaluation of control measures

Abstract

A large-scale foot-and-mouth disease (FMD) epidemic occurred in Japan in 2010. The epidemic arose in an area densely populated with cattle and pigs, continued for 3 months, and was contained by emergency vaccination. In this study, a mathematical simulation model of FMD transmission between farms was developed to generate the disease spread in the affected area. First, a farm-distance-based transmission kernel was estimated using the epidemic data. The estimated transmission kernel was then incorporated into the transmission model to evaluate the effectiveness of several control measures. The baseline model provided a good fit to the observed data during the period from imposition of movement restrictions until the implementation of vaccination. Our simulation results demonstrated that prompt culling on infected farms after detection could contribute to reducing the disease spread. The number of infected farms decreased to 30% of the baseline model by applying the 24-h prompt culling scenario. The early detection scenario resulted in a smaller-sized epidemic. However, the results of this scenario included a 35% chance of large-scale epidemic (more than 500 infected farms), even when the disease was detected 14 days earlier than in the baseline model. As additional options, preemptive culling could halt the epidemic more effectively. However, the preemptive culling scenario required substantial resources for culling operations. The 1-km preemptive scenario involved more than 50 farms remaining to be culled per day. Therefore, preemptive culling scenarios accompanied some difficulties in maintaining a sufficient capacity for culling in the affected area. A 10-km vaccination 7 days after the first detection of the disease demonstrated the potential to contain the epidemic to a small scale, while implementation of a 3-km vaccination on the same day could not effectively reduce epidemic size. In vaccination scenarios, the total number of farms that were either culled or vaccinated exceeded that of the baseline model. Vaccination scenarios therefore posed a problem of appropriate management of many vaccinated animals, whether these vaccinated animals would be culled or not. The present FMD transmission model developed using the 2010 FMD epidemic data in Japan provides useful information for consideration of suitable control strategies against FMD.

Keywords: Control measures; FMD epidemic in Japan 2010; Mathematical model; Transmission kernel.