Genetic divergence of enterovirus D68 in China and the United States.

The largest outbreak of human enterovirus 68 (EV-D68) infections associated with severe respiratory illness and neurological complications emerged from the United States in 2014. China reported the circulation of EV-D68 since 2006, but these cases were sporadic and did not display neurological symptoms. Yet viral determinants responsible for the difference in prevalence between China and the U.S. were not clear. We analyzed the genome of 64 reported Chinese EV-D68 strains and found that genogroup replacement has occurred in China since 2006. The six coding mutations (M291T, V341A, T860N, D927N, S1108G and R2005K) associated with neurovirulence reported in American strains were not found in Chinese strains. Moreover, 2014 Chinese strains had a unique R220A mutation in the puff region of VP2 while R220E mutation occurred in other strains. Like other enteroviruses, the loop sequences of the domain X and Y in the 3'-UTR of the Chinese strains are complementary. However, the X loop sequences of the 2014 American strains were not complementary but identical to Y loop sequences. These results indicate that different EV-D68 strains circulated in China and America and the mutations might be responsible for different prevalence. Our findings also provide new evidence for the sequence diversity of EV-D68.