Researchers at the University of Texas Medical Branch at Galveston (UTMB) have discovered a quick new way that mosquitoes can pass West Nile virus to each other. The new study challenges fundamental assumptions about the virus' transmission cycle and may help explain why it spread so rapidly across North America despite experts' predictions that it would progress more slowly or even die out. In the conventional understanding of West Nile transmission, mosquitoes acquire the virus when they bite birds with high levels of virus (or "high viremia.") in their blood. Those levels are reached several days after the birds are initially infected by other mosquitoes. But experiments at UTMB show that when infected and uninfected mosquitoes feed simultaneously on previously uninfected laboratory mice, the virus can pass from mosquito to mosquito within an hour.

"We were amazed to see that it could happen," said UTMB associate professor Stephen Higgs, lead author of a paper on the discovery that will be published online in the Proceedings of the National Academy of Sciences the week of June 6. "It is basically a brand-new component of the virus' life cycle."

In the paper, Higgs and his co-authors--UTMB graduate student Bradley S. Schneider, senior research associate Dana Vanlandingham, research assistant Kimberly A. Klingler and Ernest A. Gould of the United Kingdom's Centre for Ecology and Hydrology--note that although such "non-viremic transmission" (that is, transmission before virus can be detected in the blood) has been observed in cases involving viruses transmitted by ticks, it has never before been documented in a virus carried by mosquitoes.

To determine whether West Nile virus could be transmitted non-viremically, the researchers placed an anesthetized, uninfected lab mouse on a mesh-topped container holding infected "donor" mosquitoes, which fed on the mouse through the mesh. Five minutes later, they moved a second mesh-topped contai
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Contact: Jim Kelly
jpkelly@utmb.edu
409-772-8791
University of Texas Medical Branch at Galveston
6-Jun-2005

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