How Dangerous is a Mosquito Bite? More so than Previously Believed

Researchers at the University of Texas Medical Branch at Galveston (UTMB) have made a discovery that gives some new insight into West Nile Virus. They have found that if a person is bitten by a mosquito that does not have the virus and then at some later time are bitten by an infected mosquito they would have a higher risk of the disease being worse.

They base this conclusion on tests that were done with lab mice that showed this result.

West Nile Virus is contracted from the saliva of the mosquito. The saliva has an effect on the immune system and makes the West Nile Virus even worse. This study shows that even the saliva from uninfected mosquitos can have an effect on the intensity of the infection.

The mice were sedated and then were exposed to and bitten by from 15 to 20 Aedes aegypti mosquitoes. This went on for an hour once a week. Then they were exposed to just one West Nile virus-infected mosquito. They also exposed a control group that had not been bitten by the uninfected mosquitoes to a West Nile virus-infected mosquito.

The results showed that 68% of the mice who were exposed to both types of mosquitoes in two weekly sessions died from the West Nile Virus. Those who were exposed for four weeks, had a 91% death rate. With the mice who only were exposed to the West Nile carrying mosquitoes, the death rate was 27%. They also analyzed the responses in the immune systems of the mice and there was a big difference between the two groups.

What they noticed was that there was an increase in one of the immune signaling molecules called interleukin-10 in the mice who had been exposed to both types of mosquitoes. This response to the saliva causes a change in the immune response at the place where the virus first strikes and when they are bitten by an infected mosquito, the virus takes advantage of it.

These results came as a big surprise because in the case of other diseases transmitted by an insect bite have shown that being previously bitten by an uninfected insect actually gave protection from the infection. For instance in one test mice were allowed to be bitten by sand fleas that were uninfected and they were protected from developing cutaneous leishmaniasis

The lead researchers are Brad Schneider, a UTMB alumnus who is now a postdoctoral fellow at the Institut Pasteur in Paris, UTMB professor Stephen Higgs and Dr. Lynn Soong. The rest of the team is graduate students Charles E. McGee, Jeffrey M. Jordan and Heather L. Stevenson

The research was funded by grants from the Centers for Disease Control and Prevention and the National Institutes of Health.

Source: University of Texas Medical Branch at Galveston http://www.eurekalert.org/