Based on the evidence in mouse models suggesting a critical neuroprotective role for CCR5 during flavivirus infections, several epidemiologic studies have been conducted to evaluate the role of CCR5 in humans, specifically testing for the complete loss-of-function mutation CCR5Δ32. This phenotype is commonly found at 10% allele frequency in the US (Zimmerman et al., 1997; Berger et al., 1999). This evidence concerns the gene CCR5 and Flavivirus Infections.