Clark County mosquito crews on West Nile virus warpath

Breed that can carry potentially fatal disease arriving in local area

By Marissa Harshman, Columbian health reporter

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photoAn environmentally safe biological larvacide is used to prevent mosquitoes that can carry the West Nile virus from hatching. Crews from the Clark County Mosquito Control District are spraying all retention ponds and catch basins in the county.

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The floodwater mosquitoes feasting on Clark County residents the past few weeks are beginning to die off and should be out of residents’ hair in the next couple of weeks.

But mosquito experts are warning that residents aren’t in the clear yet.

With the departure of the nuisance mosquitoes comes the arrival of another breed of the blood-sucking skeeters: the Culex variety that can carry the West Nile virus.

Clark County Mosquito Control District crews have begun treating retention ponds and catch basins throughout the county to try and protect residents from the disease-carrying mosquitoes. Every pond and basin will be treated at least once, said Steve Kessler, operations manager for the district.

Crews have tested mosquitoes in the county and have not found any to be positive for the West Nile virus. Elsewhere in the state, officials have found 35 positive cases of the virus in tested mosquitoes.

West Nile virus can be a serious, even fatal, illness. People of all ages can be infected by the virus, most commonly transmitted by bites from infected mosquitoes, according to the Washington State Department of Health. Horses, birds and other animals can also be infected. Last year was the state’s most active year for West Nile virus, with 38 human cases identified and the first human death, according to the health department.

Mosquitoes carrying the virus typically hatch about a month after the floodwater mosquitoes, once temperatures rise and water warms up, Kessler said. The disease-carrying Culex mosquitoes have a shorter life-span than their floodwater cousins, which live for about two weeks, and the county won’t experience an unusually large number of disease-carrying mosquitoes, he said.

“They don’t have the tenacity that the floodwater mosquitoes have,” Kessler said.

Clark County’s long, wet spring, followed by a warm-weather streak, created the perfect climate for floodwater mosquito hatching. That, Kessler said, meant multiple hatchings of the nuisance mosquitoes and a sudden surge in the skeeter population. Earlier this month, the district had received three times as many calls requesting service compared with the same time last year.

In the past couple of weeks, though, the population and calls have started to ebb.

“The call volume has almost completely dropped off,” Kessler said.

But the high number of calls regarding the nuisance skeeters put district crews two to four weeks behind schedule in prevention methods for the disease-carrying mosquitoes, he said.

Even though floodwater mosquitoes are becoming less of a nuisance, Kessler encourages residents to continue prevention measures.

Anyone outside at dusk should wear light-colored, long-sleeved shirts and use bug repellent on any exposed skin, he said.

Residents should also beware of any standing water, which can serve as a breeding ground, on their property. Bird bath water should be changed twice a week, water on top of pool covers should be removed and buckets of water should be emptied, Kessler said.

“If they don’t have water,” he said, “you won’t have mosquitoes.”

Marissa Harshman: 360-735-4546 or marissa.harshman@columbian.com.