West Nile virus’ spread watched

Molly Ball and Mary Manning

Monday, Aug. 16, 2004 | 11:09 a.m.

With seven new probable cases of West Nile virus reported in Clark County, officials are monitoring the disease's spread but say there is no way to tell how far-reaching the outbreak will be.

The seven new cases, reported on Friday, were in addition to three previously reported cases in the county, two confirmed at federally approved labs and one that was still being tested.

Results on the probable cases are expected late next week; so far, no Nevada case sent off for testing has come back negative for the mosquito-borne virus.

This is the first year West Nile has been found in Nevada.

The state Health Division on Friday also reported confirmation of two cases, plus another probable case, in Churchill County.

In addition, a dog died in Washoe County from the disease, the second case of canine infection reported in Washoe County, state health officials said. The animal was 15 years old and had a weakened immune system.

The first dog, a dachshund in Washoe Valley, was diagnosed with West Nile virus and is recovering.

The federal Centers for Disease Control and Prevention reported fewer than 40 dogs and only one cat infected with West Nile virus nationwide. While the virus can infect humans, birds and horses, it is rare in dogs.

It is too soon to say how the virus will proceed here and whether it will explode or fizzle out, officials say. But the disease, which can be deadly in rare cases, is on a familiar path.

"We're seeing the same type of spread" as eastern states saw in 1999, Martha Framsted, spokeswoman for the Nevada Health Division, said on Friday. "West Nile virus starting out in mosquitoes, then going to birds and equines, then going to humans.

"It seems to be following the same type of pattern," she said.

Since it appeared in the American northeast in 1999, West Nile has marched steadily south and west across the U.S., she noted.

Officials tentatively predict a peak in mid- to late August, but many factors could change that, Framsted said. The mosquitoes that spread the virus breed during the summer months, their life cycles attuned to air temperatures -- so an unseasonably hot fall could extend their presence.

But because the disease cannot be spread from person to person -- people can only get it from being bitten by infected mosquitoes -- its spread depends heavily on environmental factors, which are different for different areas, said Patricia Rowley, epidemiology manager for the Clark County Health District.

"It's difficult to draw parallels with other states because they have distinctly different climates and environments," Rowley said.

The Las Vegas Valley has the advantage of being so dry that there are few naturally occurring pools of standing water where mosquitoes can breed, she said.

A lack of drainage culverts makes for frustrating street flooding when it rains, but it also means the water doesn't collect in pools, which quickly become maternity wards for mosquitoes.

"If we had wooded areas, with lakes and bogs, it would be much more difficult" to control the virus, Rowley said.

The valley's most likely sources of mosquitoes are desert washes, flood basins, drainage channels and abandoned swimming pools.

City officials in Henderson are ripping out an abandoned baseball field at the Arroyo Grande Sports Complex because its swampy vegetation was found to be breeding mosquitoes. The boggy field, complete with cattails and other marsh plants, abuts a flood basin. In a random sampling, 22 out of a sample of 156 mosquitoes -- 14 percent -- were found to be infected with West Nile.

While West Nile continues to spread, it did not concern many people who were outdoors enjoying the lower-than-normal temperatures in local parks on Sunday.

Debbie Berg, who had been out in Arroyo Grande Sports Complex Saturday and Sunday enjoying a softball tournament, said all the players had been sprayed with insecticide containing DEET and no one had seen a mosquito.

"We knew about it," Berg said. "We came with bug spray. You can't hide from it."

Bicyclist David Eich rides about 20 miles a day, through swarms of gnats and flies. He wasn't wearing insect repellent on Sunday when he stopped to rest in Sunset Park.

"I heard about it (West Nile virus)," Eich said. "On a scale from 1 to 10, I'm at a 6," he said of his "worry scale."

"I'm from Oklahoma," the 10-year resident of Las Vegas said. "I had more mosquitoes than we knew what to do with when I was growing up. We don't have any bugs here."

After eight years in Las Vegas, avid camper Donald Brakeman, an actor, said he had cut back on outdoor trips this summer.

"I'm not worried," Brakeman said as he completed a walk in Sunset Park. "I know there's a risk."

County officials are concentrating their control efforts on unmaintained backyard pools, treating them with pellets that kill mosquito larvae.

But whether those methods are succeeding in keeping the lid on West Nile or whether they are failing to make a dent cannot yet be known, Rowley said. There are just too few cases, and investigations have not been completed to determine where the infected people were bitten by mosquitoes.

Another factor in the sudden discovery of seven new cases, Rowley said, is that community awareness may be prompting more doctors to order tests for West Nile when they see the symptoms that can represent West Nile fever.

Of the seven new probable cases in Clark County, five are older than 50 and two are younger than 50. People older than 50 are more likely to get sick from the virus.

One of the seven saw a doctor but was not hospitalized. Three have been released from the hospital, and three are still hospitalized, the Health District said on Friday.

Of the two confirmed cases, one has recovered and the other remains hospitalized in stable condition with meningitis and encephalitis, swellings of the brain and spinal cord that are the hallmarks of the disease's severest form.

The Clark County Health District suggests the following to avoid mosquito bites: