County targets swampy pools in West Nile struggle

Molly Ball

Monday, Aug. 9, 2004 | 11:12 a.m.

To report stagnant pools or other standing water, call Vector Control at (702) 455-7543.

In the face of two more probable cases of West Nile virus, Clark County officials are cracking down on swampy pools but have no plans to spray pesticides to kill the mosquitoes that carry the disease.

The two latest victims are residents older than 50, Clark County Health District spokesman David Tonelli said Sunday. People older than 50 are slightly more likely to get sick from the virus.

The two new probable cases of West Nile virus, if confirmed, would bring the total of human cases in Nevada to five, health officials said Sunday.

The cases are unrelated, and it was not known where the victims picked up the disease, which is spread by infected mosquitoes. One of the victims was hospitalized, while the other had seen a doctor and been sent home, Tonelli said.

Blood samples from the two were sent on Aug. 4 to a regional laboratory certified by the federal Centers for Disease Control and Prevention in Richmond, Calif., for testing to confirm whether they are cases of West Nile. Results are expected by Wednesday, Tonelli said.

Officials are testing the areas around the victims' homes for infected mosquitoes, but Health District officials are refusing to identify those areas because, they said, they don't yet know whether the victims were infected near their homes.

Infected mosquitoes have been found in the Las Vegas ZIP codes 89130 and 89122, Logandale ZIP 89021 and Tonopah's 89049, the Health District said in a statement.

Of the two Nevadans who were confirmed to be infected, one was in Clark County for the entire span of the virus' incubation period, the three to 14 days after being bitten that the virus' symptoms take to appear. The other victim "had a travel history that included California" during that span, Tonelli said.

To arrest the virus' spread, the Health District will now give just 24 hours' notice to owners of brackish, overgrown pools before intervening.

Mosquitoes breed in stagnant water, including that of swimming pools that have not been maintained. There are about 65,000 private pools in the Las Vegas area.

Vector Control officials from the Public Works Department have in recent weeks been working to prevent mosquitoes from breeding in such pools by treating the water with larvicide, a substance that kills mosquitoes' young. But Vector Control workers often meet resistance -- or silence -- from the pools' owners, Tonelli said.

When that happens, Vector Control does not have the authority to enter the pool without permission. But the Health District does, so the two have teamed up. Once 24 hours have passed, officials will seek a court order allowing them to go in and treat the pool, Tonelli said.

Unlike Southern California and Arizona, which have large populations of adult mosquitoes that officials are spraying, Clark County specialists are trying to interrupt the mosquito breeding cycle, Tonelli said.

More than 200 calls reporting standing water, including unmaintained pools, have come in since July 20, when West Nile was first found in the state by way of a dead crow in Washoe County, Richard Hicks, supervising entomologist for Vector Control, said.

Owners of improperly maintained pools will not be fined or charged for the larvicide because the treatments are part of normal operations, Tonelli said.

Over the weekend in Northern Nevada, Lyon County officials declared a state of emergency because of the spread of the West Nile virus.

Twenty-one birds, five horses and 18 mosquitoes all tested positive for the virus as of Friday in the rural county known for its ranches, Nevada Agriculture Department officials said.

The first canine case in Nevada was confirmed in Reno as well, though state veterinarian Dr. David Thain said dogs and cats generally are not susceptible to the disease, even if they are bitten by infected mosquitoes.

In Phoenix and several California counties, pesticides have been sprayed in the air to kill mosquitoes. But Hicks said there were no plans to do that here because the number of cases was small.

In Arizona, the worst state in the nation for West Nile, 246 people had become ill and three had died from the virus as of last week, most in the area around Phoenix. In addition to larvicide efforts, officials there are increasing their use of trucks that puff out a "fog" of pesticide.

While larvicide kills young mosquitoes before they can even fly, the pesticides kill adult mosquitoes. But they cannot be precisely targeted, and some suspect they may have health effects on people and animals.

"When you have the disease spreading rapidly, as you do in some of those areas, you have to resort to some of those methods," Hicks said. But such methods are a last resort, he said.

"Our program has been to try to prevent adult (mosquito) emergence in the first place," he said. He said officials had no threshold number of cases after which they would start to use pesticide.