Earlier bites by uninfected mosquitoes boost West Nile deaths i...( GALVESTON Texas Theres one more rea...)

GALVESTON, Texas Theres one more reason to try to avoid being bitten by mosquitoes, scientists have discovered: bites from mosquitoes that arent infected by the West Nile virus may make the disease worse in people who acquire it later from West Nile-infected mosquitoes.

Researchers from the University of Texas Medical Branch at Galveston (UTMB) announced their discovery in a paper published online by the journal PLoS ONE. In the paper, they describe experiments showing that lab mice on which mosquitoes have previously fed are far more likely to die from West Nile infection than are mice unexposed to such mosquito bites.

The effect is induced by mosquito saliva, according to UTMB professor Stephen Higgs, one of the papers senior authors.

This virus is transmitted from mosquitoes in saliva, and wed already demonstrated that mosquito saliva has an effect on the vertebrate immune system that makes West Nile infection worse, Higgs said. What this new work shows is that the saliva delivered by even earlier feedings can also alter the course of the infection. This is important, because in natural situations in many parts of the world Southeast Texas, for example animals and some people are being exposed to mosquito feeding almost continuously.

In their experiments, researchers exposed sedated mice to feeding by between 15 and 20 Aedes aegypti mosquitoes for an hour once a week. Scientists then allowed a single West Nile virus-infected mosquito to feed once on each of these mice and also on each of a control group of mice that were previously unbitten by mosquitoes.

The results were striking: 68 percent of mice exposed to two weekly mosquito feedings died of West Nile virus, and those exposed to four weekly mosquito feedings suffered a 91 percent mortality rate. By contrast, the virus killed only 27 percent of the mice previously unexposed to saliva from mosquitoes that were free of West Nile infection. Analyses of res
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