Wednesday, June 19, 2013
Week’s heavy rain likely lessened West Nile mosquito population
It washes out nests and disrupts breeding grounds.
Heavy rain that hit the area early this week is just what's needed to keep mosquitoes prone to the West Nile virus under control.
Collin County chief epidemiologist Peggy Wittie said rain helps wipe out the nests of Culex quinquefasciatus or “drought mosquitoes” that carry the virus in this area and thrive in hot, dry conditions.
"We'll get more mosquitoes of other types, but they don't carry the virus," she said. "So rain is our friend."
The rain kills the drought mosquitoes by washing out the nests they create in storm drains and gutters and by agitating pools of stagnant water they need for reproduction. Wittie said the population of those mosquitoes has been shown to decrease with rainfall of more than an inch, and that heavy rain will keep their numbers down for two weeks.
Surveillance of drought mosquitoes began in April, a month earlier than normal, in many cities. Mosquito season runs from June through September, the hottest months of the year when the insects thrive.
Wittie said the prime area for drought mosquito breeding is a pool of water less than a foot deep that doesn't see much agitation. That's why the county is urging residents to drain pools of standing water on their property in wading pools, bird baths and other places.
So far this year, no infected mosquitoes have been found in Collin County, which had 76 human cases of the virus and four deaths last year. Infected mosquitoes were found in Richardson in April, and the positive tests were followed by ground spraying.
Dallas started spraying for mosquitoes this week. CBS 11 reported Tuesday that mosquitoes from the southern part of the city tested positive for the virus after spraying for population control was already underway.
While mosquitoes may be the avenue by which West Nile reaches people, they aren't the source of the virus. Mosquitoes get the virus from infected birds such as blue jays, crows and other birds from the corvidae family, which are common carriers.
“We're not seeing as many [of those birds] so far this year, so maybe, knock on wood, we won't have as much of a problem this year,” Wittie said.
Most people infected with the virus have no symptoms, according to the Centers for Disease Control and Prevention. About one in five people infected with the virus develop a fever, and less than one percent become seriously ill with encephalitis or meningitis. About 10 percent of those who become seriously ill from West Nile will die.
There have been two human cases of the virus in Texas this year. The state had 1,868 human cases of West Nile last year and 89 deaths.
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