VOA常速英语:Dallas Attacks West Nile Virus by Land, Air

DALLAS — Officials in Dallas, Texas, have stepped up efforts to combat West Nile virus after the deaths of 10 people there.

West Nile has struck all over the continental United States in recent weeks, but Dallas has been the hardest hit.

Officials there are fumigating on the ground and in the air, targeting specific mosquitoes which spread the disease.

The aerial and ground fumigation programs are blanketing around 1,400 square kilometers of the county, but don't target all mosquitoes.

Laura McGowan, who works with Clarke, the company contracted to carry out the aerial operation, says two local species spread West Nile virus.

“The ones that we are targeting right now are the Culex mosquitoes here in Dallas," she says. "Culex quinquefasciatus and Culex Tarsalis.”

The mosquitoes, known generally together as the Southern House Mosquito, lay eggs in water, which turn to larvae and finally into full-grown flying bloodsuckers.

They come out at dusk each night. So that's when the planes fly and drop a fine mist of a concoction called DUET which, according to McGowan, attracts the mosquitoes and kills them.

“Our average droplet size is smaller in diameter than a human hair, so that is designed to specifically interact with the mosquito biology," she says. "That is how we know we are avoiding non-target insects, by both the time of the day we are applying as well as the size of the droplets.”

McGowan says some areas may need to be sprayed two or three times to make sure no significant numbers of mosquitoes or their larvae remain.

But some areas may need only one application, according to the director of Dallas County Health and Human Services.

“Especially if we have not had one positive human case or a positive mosquito pool, one application would be sufficient,” Zachary Thompson says.

Weekend rains halted some of the spraying efforts and left puddles of water where more mosquitoes can breed.

While streams and ponds are perfect breeding grounds for mosquitoes, experts say even a small amount of water on a city street can support larvae.

Local officials are asking people to look for discarded containers that might contain stagnant water that could breed mosquitoes and get rid of them.

McGowan stresses the need for public awareness of the threat and what to do to avoid the disease.

“It only takes one West Nile mosquito to make someone sick," she says. "So we want to make sure people put on personal protection, that they do avoid being out at dusk and dawn, and we are still very early in the West Nile season.”

Measures to fight the spread of West Nile virus will not end until the first good frost subdues mosquitoes, but that could be more than two months from now.