Viral interference during coinfection and sequential infection of enterovirus A71 and coxsackievirus A16.

Hand, foot and mouth disease (HFMD) is a common childhood infection caused by enteroviruses including enterovirus A71 (EV-A71) and coxsackievirus A16 (CVA16). These viruses often co-circulate, resulting in potential viral interference which could impact virus transmission, virulence, and EV-A71 vaccine effectiveness. Experimental evidence to support these findings is lacking. Epidemiology and seroprevalence data for EV-A71 and CVA16 reveal trends suggestive of viral interference between the two viruses. Coinfection with both EV-A71 and CVA16, or sequential infection of EV-A71 followed by CVA16, were performed in rhabdomyosarcoma (RD) cells and compared with single virus infection. In RD cells, coinfection did not affect virus replication while prior EV-A71 infection inhibited CVA16 replication at 24 h post-infection. BALB/c mice were infected with mouse-adapted EV-A71 (MP4), EV-A71 and CVA16 simultaneously or sequentially. In mice, coinfection reduced mortality (40 %) while prior EV-A71 infection reduced sequential MP4-induced (40 %) and CVA16-induced (20 %) mortality in contrast to 100 % mortality in single virus-infected mice. Coinfection reduced EV-A71 MP4 viral RNA in limbs and brains, triggering innate immune activation with altered interferon-stimulating genes (ISGs) and cytokine expression. Prior EV-A71 infection suppressed CVA16 replication in limbs and brains, caused limited histopathological changes and unchanged innate immune responses. Prior EV-A71 infection suppressed MP4 antigens as evidenced by histological findings and elevation of IFITM3, ISG15, RSAD2, interleukin (IL)-1β and IL-6 expressions. We have experimentally demonstrated viral interference between EV-A71 and CVA16 during coinfection and sequential infection. A coadministered or sequential EV-A71 and CVA16 vaccine could provide broad innate immune protection.