A Single Mutation in the VP1 of Enterovirus 71 Is Responsible for Increased Virulence and Neurotropism in Adult Interferon-Deficient Mice

Hand, foot, and mouth disease (HFMD) has spread throughout the Asia-Pacific region, affecting millions of young children, who develop symptoms ranging from painful blisters around their mouths and hands to neurological complications. Many members of the genus Enterovirus (family Picornaviridae) cause HFMD. Enterovirus 71 (EV71) is one of the primary causative agents and has been linked to severe disease. Vaccine efficacy and pathogenesis studies for EV71 have been limited because there is a lack of suitable animal models. Previously, we generated a mouse-adapted EV71 (mEV71) capable of infecting 12-week-old interferon receptor-deficient AG129 mice and used the model to evaluate the efficacy of candidate HFMD vaccines. Here, we present data investigating the genetic correlates of EV71 adaptation and characterize the virus's tissue tropism in mice. Using reverse genetics, a VP1 mutation (K244E) was shown to be necessary for mEV71 virulence in adult mice. Another VP1 mutation (H37R) was required for mEV71 recovery on rhabdomyosarcoma (RD) cells. Viral loads determined by real-time reverse transcription (RT)-PCR confirmed the presence of mEV71 in the sera and multiple organs of mice. Histological analysis revealed signs of meningitis and encephalitis, characteristic of severe human disease. The further description of this model has provided insight into EV71 pathogenesis and demonstrates the importance of the VP1 region in facilitating mEV71 adaptation. IMPORTANCE EV71 is a reemerging pathogen, and little is known about the genetic determinants involved in its pathogenesis. The absence of animal models has contributed to this lack of knowledge. The data presented here improve upon the existing animal models by characterizing a mouse-adapted strain of EV71. We determined that a VP1 mutation (K244E) was needed for EV71 virulence in adult AG129 mice. While this mutation was found previously for EV71 adaptation in 5-day-old BALB/c mice, neurotropic disease did not develop. Using interferon-deficient mice, we raised the age of susceptibility beyond 6 weeks and provided clear evidence that our model mimics severe human infections. The model can be exploited to identify determinants of EV71 virulence and to reveal molecular mechanisms that control the virus-host interaction, especially those associated with neurotropic disease. Furthermore, these data provide useful information regarding the importance of VP1, specifically position 244, in host adaptation and tissue dissemination.