July 8, 2005

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COLLEGE STATION – Even with the recent dry weather, Texans should still take precautions against mosquito-borne diseases, advised an expert with the Texas Agricultural Experiment Station.

Dry weather is perfect for the southern house mosquito, the major urban vector of West Nile Virus and an older virus, St. Louis encephalitis, said Dr. Jim Olson,.

Like its name implies, the southern house mosquito likes to enter houses. And even though it feeds primarily on birds, when the mosquito is inside a house, it will feed on the next-best thing: humans. That is how the West Nile and St. Louis encephalitis viruses are transferred to humans, Olson said.

"The dry weather is perfect because about the only water we have left now is standing and stagnant," he said. "This is the type of water the (southern house) mosquito likes to lay its eggs in and the larvae like to develop in."

And, because this is about the only kind of water left, birds are congregating where the water – and the mosquitoes – are. This proximity amplifies the ability of the mosquitoes to infect birds with the virus.

"So, in essence, we have little virus incubators going on," Olson said.

West Nile virus has been found in mosquito populations from the Houston-Beaumont area along the Gulf Coast and East Texas to Swisher County between Amarillo and Lubbock to El Paso and even in Austin, he said.

In addition, two human cases in the Houston area – one from a mosquito bite and the other traced to a blood donation – have been found. Some cases have also occurred in horses, he said.

St. Louis encephalitis has also"reared its ugly head again," he said.

Testing procedures have found a pool of infected mosquitoes in Houston, and a possible human case has been reported in the Lower Rio Grande Valley.

Texans may have been lulled into a false sense of security this year because the major backyard mosquito that bites humans, the Asian tiger mosquito, has not developed large populations, Olson said. Without mosquitoes biting on a regular basis, people may think the insects are not a concern.

"This is, of course, wrong," Olson said. "It just not the Asian tiger mosquito that is active."

Also active, but perhaps not biting as much, are the species like the southern house mosquito that like to breed in standing, stagnant water, he said.

He urged everyone to take all the precautions necessary to prevent mosquitoes from entering homes and breeding on their on property or premises.

"And continue protecting yourself when you are outdoors during times of the day and evening when mosquitoes are actively out seeking blood meals," he said.

"Keep up the vigilance. We're not out of the woods yet."