- The Washington Times - Tuesday, August 17, 2004

PHOENIX (AP) — With triple-digit heat and nearly nonexistent rainfall, Phoenix seems an unlikely spot for this year’s West Nile virus epicenter. Yet, federal health officials say Arizona is the only state where the mosquito-borne virus is an epidemic.

“Minnesota may be the land of a thousand lakes, but we’re the land of thousands of abandoned swimming pools,” says Will Humble, head of disease control for the Arizona Department of Health Services.

Those swimming pools, plus irrigation canals that slice through parts of the city, patio misters and lush lawns designed to remind transplants of gardens they left behind have inadvertently turned neighborhoods into oases for mosquitoes.

“It didn’t use to be this bad. You never saw a mosquito,” said resident Gary Clark, 62, who takes his morning walk in an area where a high number of cases have been reported. “It’s even trouble sitting out in your back yard now.”

So far this year, at least 290 of the nation’s more than 500 West Nile cases are in Arizona; three of the 14 deaths were in Arizona. Nearly all the cases have been in the state’s most populous county, Maricopa, which includes the Phoenix metropolitan area.

State health officials estimate at least 30,000 Arizonans may have the virus without knowing it. Some people never have symptoms at all. Only about 1 percent of West Nile victims develop the potentially dangerous inflammation of the brain or spinal cord — meningitis or encephalitis.

Last year was the first time the virus appeared in areas west of the Continental Divide. It hit Colorado hard and drifted slowly into Arizona’s northeastern tip, then down south. It’s now spreading in California, where at least 116 cases have been reported and at least five persons have died.

Several factors have contributed to Arizona’s outbreak.

“It’s like the planets, everything has to align” for an outbreak to occur, said John Roehrig, chief of the Centers for Disease Control’s arboviral diseases branch in Fort Collins, Colo.

While more humid climates have more mosquitoes, health officials there also are more prepared to deal with “nuisance mosquitoes,” while Arizona isn’t.

And while Arizona doesn’t have a lot of mosquitoes because of long stretches of 100-plus degree days, one type of mosquito thrives here: the Culex tarsalis. The species is one of the best carriers of West Nile virus.

It thrives in suburban settings and likes to feed on human blood.

The species can breed in small pools of standing water, such as in wheelbarrows, kiddie pools and plant saucers. Since the species is so dominant here, it doesn’t have to compete with other types of mosquitoes for breeding spots.

The water that people surround themselves with to combat the heat can be another major factor. From the air, pools form a checkerboard pattern across the desert landscape.

Of the approximately 600,000 residential swimming pools in the state, state health officials estimate about 10,000 are potential breeding grounds for mosquitoes.


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