Virus Excretion from Foot-And-Mouth Disease Virus Carrier Cattle and Their Potential Role in Causing New Outbreaks

Abstract

The role of foot-and-mouth disease virus (FMDV) carrier cattle in causing new outbreaks is still a matter of debate and it is important to find out these carrier animals by post-outbreak serosurveillance to declare freedom from FMDV infection. In this study we explore the differences in viral shedding between carrier and non-carrier animals, quantify the transmission rate of FMDV infection from carriers to susceptible animals and identify potential viral determinants of viral persistence. We collected nasal and saliva samples from 32 vaccinated and 7 unvaccinated FMDV carrier cattle and 48 vaccinated and 13 unvaccinated non-carrier cattle (total n=100) during the acute phase of infection (up to 28 days post-challenge) and then from limited number of animals up to a maximum 168 days post-challenge. We demonstrate that unvaccinated cattle excrete significantly higher levels of virus for longer periods compared with vaccinated cattle and this is independent of whether or not they subsequently become carriers. By introducing naïve cattle in to the FMDV carrier population we show the risk of new outbreaks is clearly very low in controlled conditions, although there could still be a potential threat of these carrier animals causing new outbreaks in the field situation. Finally, we compared the complete genome sequences of viruses from carrier cattle with the challenge virus and found no evidence for viral determinants of the carrier state.

Genetic and antigenic variation of foot-and-mouth disease virus during persistent infection in naturally infected cattle and Asian buffalo in India

“…The evolutionary rate estimated in this study was similar to the rate reported for other serotype O carrier viruses (2.6 × 10 -2 s/s/y;(25)).In contrast, the rate reported in this study was an order of magnitude faster than the rate reported for O/ME-SA/Ind2001 outbreak isolates collected in India between 2000 – 2013 (6.338 × 10 -3 s/s/y;(41)). Similarly, previous studies have shown the rate of evolution of serotype C carrier viruses was an order of magnitude faster than the rate reported for serotype C outbreak viruses collected over a period of six decades (59, 64).…”

“…Several studies have reported the antigenic and genetic variants of FMDV in the virus population recovered from persistently infected cattle and buffalo under experimental conditions (12, 25, 28-32) or under natural field conditions (14, 17, 21, 33-37). Although within-host genetic variation is common during persistent infection, no consistent genetic changes associated with persistent infection have been identified across studies.…”

Quantitative characteristics of the foot‐and‐mouth disease carrier state under natural conditions in India

“…Additionally, a variable proportion of animals in a herd may be subclinically infected and do not show any clinical signs of infection. This phenomenon is most common amongst vaccinated animals (McVicar & Sutmoller, ; Parthiban, Mahapatra, Gubbins, & Parida, ; Stenfeldt, Eschbaumer et al., ). In some clinically and subclinically infected ruminants, FMDV can be isolated from oropharyngeal fluids and/or tissues >28 days after infection.…”

Foot‐and‐mouth disease virus transmission dynamics and persistence in a herd of vaccinated dairy cattle in India

“…Such persistently infected animals from which virus can be isolated at least 28 days post‐infection are defined as “FMDV carriers.” The duration of this carrier state may vary from months to years (Hayer et al., ; Tenzin, Dekker, Vernooij, Bouma, & Stegeman, ). Although transmission from persistently infected cattle has not been proven under experimental conditions (Ilott, Salt, Gaskell, & Kitching, ; Parthiban, Mahapatra, Gubbins, & Parida, ), the presence of FMDV carriers in a population can severely impact foreign trade of all animal products (Kitching et al., ). In addition, the dynamics of the FMDV carrier state is relatively understudied in field conditions (Barend et al., ; Hayer et al., ).…”