Current concepts in persistent infections in foot-and-mouth disease: A review

Unapparent and persistent infection (carrier status) is established following Foot-and-mouth disease (FMD) outbreak. The FMD virus (FMDV) genome is highly unstable and has a great potential for antigenic variations and thus development of carrier state. The prevalence rate of carriers depends upon the species, the incidence of disease (or infection) and the immune status of the population. The carriers are responsible for FMD outbreaks in in-contact susceptible animals from which FMD virus can be recovered intermittently up to several months or years. Both naive as well as vaccinated animals exposed to live virus may develop persistent infection. Recently, it has been reported that under homologous challenge infection, use of high potency emergency vaccine (high antigen pay load) as well as treatment with interferon-α reduces the virus excretion from oropharynx and thus the carrier status in cattle and sheep. Further, serum antibody response to non-structural proteins (NSPs) of FMDV is prolonged in carrier cattle which may be exploited as a mean of detecting carrier animals in field. This is of particular importance to India since FMD-Control Programme is in operation since last about five years and is being extended during 11th Five Year Plan.