Seemingly harmless bites from mosquitoes not infected by the West Nile virus may make the disease worse in people who acquire the virus later from West Nile–infected insects, according to new research conducted at the University of Texas Medical Branch at Galveston (Schneider BS et al. PLoS ONE. 2007;2:e1171).
Through studies in mice, the investigators found that prior exposure to mosquito saliva exacerbates West Nile virus infection and increases mortality. The researchers exposed sedated mice to feeding by 15 to 20 mosquitoes for an hour once per week for several weeks and then allowed a single West Nile–infected mosquito to feed once on each mouse and also on each of a control group of mice that were not previously bitten by mosquitoes. Greater preexposure corresponded to elevated immune responses and higher mortality: groups previously exposed 2 and 4 times to uninfected mosquitoes showed 68% and 91%
mortality rates, respectively, compared with 27% mortality in unexposed mice.
Hampton T. West Nile Susceptibility. JAMA. 2008;299(1):29. doi:10.1001/jama.2007.33