An essential role of CCR5 in ameliorating the outcome of infectious diseases has been documented in trypanosomiasis [42], toxoplasmosis [43], genital herpes [44], influenza [45], flaviviral West Nile encephalitis, and JE [16–18], while a beneficial effect of CCR5 deficiency on the outcome of other infectious diseases has been postulated [23, 24, 39, 46, 47]. The gene discussed is CCR5; the disease is Japanese encephalitis.