Redefining the “carrier” state for foot-and-mouth disease from the dynamics of virus persistence in endemically affected cattle populations

Abstract

The foot-and-mouth disease virus (FMDV) “carrier” state was defined by van Bekkum in 1959. It was based on the recovery of infectious virus 28 days or more post infection and has been a useful construct for experimental studies. Using historic data from 1,107 cattle, collected as part of a population based study of endemic FMD in 2000, we developed a mixed effects logistic regression model to predict the probability of recovering viable FMDV by probang and culture, conditional on the animal’s age and time since last reported outbreak. We constructed a second set of models to predict the probability of an animal being probang positive given its antibody response in three common non-structural protein (NSP) ELISAs and its age. We argue that, in natural ecological settings, the current definition of a ”carrier” fails to capture the dynamics of either persistence of the virus (as measured by recovery using probangs) or the uncertainty in transmission from such animals that the term implies. In these respects it is not particularly useful. We therefore propose the first predictive statistical models for identifying persistently infected cattle in an endemic setting that captures some of the dynamics of the probability of persistence. Furthermore, we provide a set of predictive tools to use alongside NSP ELISAs to help target persistently infected cattle.

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

“…Similar to results of our current study, differences in extinction rates amongst subclinical T A B L E 6 Generalized estimating equation analysis of per cent of positivity results in subclinical and clinically infected animals exposed to foot-and-mouth disease virus and clinically infected animals were not significant (Hayer et al, 2017). However, findings in our study contradict the probabilistic analysis by Barend et al (2016), which suggested that the virus recovery would be expected to be close to zero by 9 months after an outbreak (Barend et al, 2016) There are only a few reports that have studied the duration of the presence of anti-NSP antibodies after natural FMDV infection in animals (Elnekave, Shilo, Gelman, & Klement, 2015;Hayer et al, 2017). In our study, more than 75% of animals were seropositive at all time points within 1 year of the outbreak.…”

“…Although transmission from persistently infected cattle has not been proven under experimental conditions (Ilott, Salt, Gaskell, & Kitching, 1997;Parthiban, Mahapatra, Gubbins, & Parida, 2015), the presence of FMDV carriers in a population can severely impact foreign trade of all animal products (Kitching et al, 2007). In addition, the dynamics of the FMDV carrier state is relatively understudied in field conditions (Barend et al, 2016;Hayer et al, 2017).…”

The role of African buffalo in the epidemiology of foot-and-mouth disease in sympatric cattle and buffalo populations in Kenya

“…No serotype A viruses were recovered from OPC cattle OPF samples collected in 2016 despite the fact that these animals were alive during the previous outbreak. Such findings are not surprising given the fact that the carrier stage, during which cattle may show persistent infection in the nasopharynx, usually lasts only one year (Hayer et al, 2018, Bronsvoort et al, 2016 and up to 28 months under some conditions . The only serotype to be recovered from OPC cattle OPF samples was serotype O, which was closely related to an outbreak of serotype O in Subukia, Nakuru, and another location from which OPC occasionally purchases animals.…”

Age‐specific infectious period shapes dynamics of pneumonia in bighorn sheep

“…In humans, the probability of persistent Hepatitis B infection decreased with age (Ott et al 2012), whereas, in some populations, the probability of persistent HPV infection increased with age (Castle et al 2005). In cattle, the probability of persistent foot-andmouth disease virus infection decreased with age (Bronsvoort et al 2016), however in wild rodents, no association was observed between the duration of cowpox infection and age (Hazel et al 2000).…”

“…In cattle, the probability of persistent foot‐and‐mouth disease virus infection decreased with age (Bronsvoort et al . ), however in wild rodents, no association was observed between the duration of cowpox infection and age (Hazel et al . ).…”