The Foot-and-Mouth Disease Carrier State Divergence in Cattle.

The existence of a prolonged, asymptomatic carrier state is a political impediment for control and potential eradication of foot-and-mouth disease (FMD). When FMD outbreaks occur, they are often extinguished by massive depopulation of livestock due to the fear that some animals may have undiagnosed subclinical infection, despite uncertainty over the biological relevance of FMD virus (FMDV) persistence. The work described here elucidates aspects of the FMDV carrier state in cattle which may facilitate identification and/or abrogation of asymptomatic FMDV infection. The divergence between animals that clear infection and those that develop persistent infection was demonstrated to occur earlier than previously established. The host antiviral response in tissues maintaining persistent FMDV was downregulated, whereas upregulation of IFN-λ mRNA was found in the epithelium of cattle that had recently cleared the infection. This suggests that the clearing of FMDV infection is associated with an enhanced mucosal antiviral response, whereas FMDV persistence is associated with suppression of the host antiviral response.