Dissecting complicated viral spreading of enterovirus 71 using in situ bioorthogonal fluorescent labeling

Enterovirus 71 (EV71), the major pathogen of hand-foot-and-mouth disease (HFDM), can cause severe neurological and respiratory manifestations in young children. Viral spread route and tissue tropism are key factors contributing to different pathogenicity of EV71, however it remains a challenge to dynamically visualize EV71 infection in vivo. The present study applies an in situ bioorthogonal fluorescent labeling strategy to track clinically isolated EV71 strains with different pathogenicity in neonatal mice. The results show that the in situ labeling strategy effectively captures EV71 viruses through in vivo bioorthogonal reaction in multiple infected organs without interfering viral spread and tissue tropism. More importantly, the in situ labeling reveals different viral dynamics, dissemination, and tissue tropism of severe case EV71 (SC-EV71) and mild case EV71 (MC-EV71), consistent with their different pathogenicity in HFDM patients. Compared with MC-EV71, SC-EV71 not only enters the blood circulation and spreads out more quickly, but also shows more significant neuronal and respiratory tropism, which certainly contribute severe neurological complications and clinical manifestations in the patient. Hence, the in situ bioorthogonal fluorescent labeling is a plausible strategy to dissect complicated process of EV71 viral spread in the early stage of infection, thereby offering great opportunities to understand its pathogenesis and develop anti-viral drugs.