Abstract—Objective: To establish and validate a humanized EV71 (FY04-R5 C1-R4) virus infection model in neonatal BALB/c mice. Methods: The EV71 (FY04-R5 C1-R4) virus, propagated in RD cells (human rhabdomyosarcoma cells), was intraperitoneally injected into 1-day-old BALB/c neonatal mice. The mice were monitored for general condition, weight gain rate, histopathological changes, and the levels of VP1 mRNA and VP1 protein. The humanized EV71 virus infection model in neonatal mice was then characterized. Results: Compared with the control group, infected mice exhibited a significant decrease in body weight gain (p < 0.05). On day 3 post-infection, symptoms such as lethargy, reduced activity, and mental lethargy were observed. As the infection progressed, motor dysfunction in the hind limbs appeared, gradually worsening. By day 7, signs of ataxia, seizures, and hind limb paralysis were prominent. The levels of VP1 mRNA and VP1 protein in the brain and lung tissues of infected mice were significantly higher than those in the control group. Histological analysis revealed areas of necrosis and neuronal loss in the brain, and in the lung, thickening of the alveolar walls, enlarged and ruptured alveoli, and infiltration of inflammatory cells, including red blood cells. Conclusion: The intraperitoneal injection of EV71 (FY04-R5 C1-R4) virus successfully established a humanized EV71 infection model in neonatal BALB/c mice. This model provides an ideal platform for the study of Hand, Foot, and Mouth Disease (HFMD). 
 

Keywords—humanized EV71 virus, neonatal mice, model, validation