Scientists Find Year-round West Nile Activity on Gulf Coast

How does the West Nile virus, which is transmitted by mosquitoes, survive the cold mosquito-free months of winter? In New York City, West Nile’s initial beachhead in North America, researchers found that the virus persisted in a kind of suspended animation in mosquitoes hibernating in sewers. But in much of the South, mosquitoes do not truly hibernate during winter — they just reduce their activity rate during cold periods, revving back up whenever the weather warms.

Understanding how the West Nile virus gets through winter under these conditions is crucial to understanding the ecology of West Nile in locations like the Gulf Coasts of Texas and Louisiana. Because of bird-migration patterns, these areas may be significant to the seasonal return of the virus to other parts of North America. In the September issue of the Centers for Disease Control and Prevention-sponsored journal Emerging Infectious Diseases, scientists at the University of Texas Medical Branch at Galveston (UTMB) and the Harris County and Galveston County (Texas) mosquito control offices report an initial step toward achieving that goal: the first successful detection of West Nile virus in mosquitoes and dead birds collected near the Texas and Louisiana Gulf Coasts between the months of November and March.

“The evidence suggests year-round West Nile activity in the Gulf region, with virus transmission persisting at a low level throughout the winter months,” said UTMB pathology professor Robert Tesh, the study’s senior author. “That’s quite different from how the virus appears to over-winter in colder regions like New York.”

The data presented in the paper derive in part from an ongoing long-term study, funded by the National Institutes of Health, on the ecology of West Nile virus in Harris County. This study was begun by UTMB and Harris County Public Health and Environmental Services in 2002, the year the same group made the first identification of West Nile virus in Texas.