West Nile Active All Year in W. Gulf Region
Mild Winters Mean No Mosquito Hibernation
Sept. 8, 2004 -- With Labor Day over, summer is winding down. But West Nile virus doesn't fade out with the change of seasons. In fact, it remains active all year in the western region of the Gulf Coast, according to a new study.
West Nile virus was detected in 11 dead birds and two mosquito pools in east Texas and southern Louisiana in the winter of 2003 to 2004.
"These findings suggest that West Nile virus is active throughout the year in this region of the United States," write Robert Tesh, MD, and colleagues in the journal Emerging Infectious Diseases.
Tesh, a professor of pathology at the University of Texas Medical Branch in Galveston, Texas, thinks he knows why.
Winters aren't cold enough to send the mosquitoes into hibernation in the areas studied: southern Louisiana and Harris County, Texas, which includes the Houston metropolitan area.
Instead, the mosquitoes just slow down, becoming relatively inactive and biding their time until warm weather returns.
It's a different story in the northern U.S.
In New York City, the West Nile virus goes into a kind of suspended animation in mosquitoes hibernating in sewers during winter.
Bird migration patterns may also help explain the virus' seasonal return to the rest of North America. Birds wintering in the western Gulf Coast region could possibly carry West Nile virus with them when they fly north in springtime.
West Nile virus was first recognized in North America in 1999 and was initially detected in Harris County, Texas, in the summer of 2002.