Serotype-Specific Transmission and Waning Immunity of Endemic Foot-and-Mouth Disease Virus in Cameroon.

Laura W Pomeroy,Ottar N Bjørnstad,Rebecca Garabed,Souley Abdoulkadiri,Hyeyoung Kim,Simon Dickmu Jumbo,Jagadeesh Bayry

doi:10.1371/journal.pone.0136642

Abstract

Foot-and-mouth disease virus (FMDV) causes morbidity and mortality in a range of animals and threatens local economies by acting as a barrier to international trade. The outbreak in the United Kingdom in 2001 that cost billions to control highlighted the risk that the pathogen poses to agriculture. In response, several mathematical models have been developed to parameterize and predict both transmission dynamics and optimal disease control. However, a lack of understanding of the multi-strain etiology prevents characterization of multi-strain dynamics. Here, we use data from FMDV serology in an endemic setting to probe strain-specific transmission and immunodynamics. Five serotypes of FMDV affect cattle in the Far North Region of Cameroon. We fit both catalytic and reverse catalytic models to serological data to estimate the force of infection and the rate of waning immunity, and to detect periods of sustained transmission. For serotypes SAT2, SAT3, and type A, a model assuming life-long immunity fit better. For serotypes SAT1 and type O, the better-fit model suggests that immunity may wane over time. Our analysis further indicates that type O has the greatest force of infection and the longest duration of immunity. Estimates for the force of infection were time-varying and indicated that serotypes SAT1 and O displayed endemic dynamics, serotype A displayed epidemic dynamics, and SAT2 and SAT3 did not sustain local chains of transmission. Since these results were obtained from the same population at the same time, they highlight important differences in transmission specific to each serotype. They also show that immunity wanes at rates specific to each serotype, which influences patterns of local persistence. Overall, this work shows that viral serotypes can differ significantly in their epidemiological and immunological characteristics. Patterns and processes that drive transmission in endemic settings must consider complex viral dynamics for accurate representation and interpretation.

Highlights

Foot-and-mouth disease virus (FMDV) is currently ranked as one of the most significant foreign animal disease threats in most major global economies [1, 2]
The World Organisation for Animal Health (OIE) classifies countries into three epidemiological categories with regards to foot-and-mouth (FMD) disease status: countries with active FMDV outbreaks, countries that are free of disease in the presence of vaccination, and countries that are free of the disease in the absence of vaccination [5]
As a preliminary investigation to check for any evidence of waning immunity after natural infection with FMDV, we categorized the subset of cattle that were serially sampled cattle (n = 31) and showed seropositivity at the first sampling event and seronegativity at subsequent sampling events

Summary

Introduction

Foot-and-mouth disease virus (FMDV) is currently ranked as one of the most significant foreign animal disease threats in most major global economies [1, 2]. Following the outbreak of FMD in the UK in 2001, which cost £4 billion to successfully eliminate the Pan-Asia O serotype [6], computational efforts have been initiated in many countries that are free of FMDV in the absence of vaccination like the United States [7,8,9,10], Australia [11, 12], and throughout Europe [13,14,15] These projects analyze threats and plan disease management strategies if an epidemic of any of the multiple circulating FMDV serotypes were to be introduced

Methods

Results

Discussion

Conclusion