North Texans have heard the high-pitched whine of mosquitoes less frequently this summer.

And with fewer of the pests out there biting, health officials say, there's been a steep drop in reported human West Nile virus infections. This summer and fall are on track to be one of the mildest seasons since the disease took hold here in 2002.

Epidemiologists and other health officials say a quiet year doesn't mean the disease is suppressed for good. Mosquitoes are still testing positive, cities and counties are still spraying to kill the insects and their larvae, and people are still being infected.

Still, even those not involved in day-to-day tracking of the disease have noticed a slowdown. Dr. Don Read said fewer new patients are attending the West Nile support group meetings he helps lead at Medical City Dallas Hospital.

He said he hoped people wouldn't make the mistake he did by not trying to avoid mosquitoes. Dr. Read nearly died in 2005 from his West Nile infection. Even now, he experiences leg weakness and fatigue.

"The fear is, this low number of cases this year can give people a false sense of security," said Dr. Read, a colorectal surgeon at Medical City. "It's well worth it to use things like DEET [repellent]. I paid a high price, and I'm still paying."

Exactly what's behind this year's decrease isn't clear. Tony Jenkins, assistant director of public health for Dallas County, said it's most likely weather patterns. But public education and continued eradication of adult mosquitoes and larvae almost certainly have contributed.

Also this year, the peak mosquito and West Nile season, usually August and September, has come later – and will stick around until cooler weather arrives.

Collin County has been most fortunate, with just one human case this year.

"Public outreach has been working in a huge fashion," said Dr. Peggy Wittie, the county's chief epidemiologist. "It would be nice if there was some bird immunity, but no one knows."

West Nile is spread when mosquitoes pick up the virus from an infected bird and then bite other animals or people, infecting them.

The primary carrier in North Texas is the Culex mosquito, also known as the house mosquito. They breed in stagnant water, including in storm drains, gutters, alleys, pots and trash can lids. Rain, especially downpours, can actually suppress them by washing out potential breeding grounds.

The Dallas area's most active West Nile season actually came in a drought year, 2006. That was also the national peak, with 4,269 human cases reported to the U.S. Centers for Disease Control and Prevention.

North Texas' experience this year is generally mirrored nationally, where human cases are down more than 60 percent from the same period last year, to 918, according to the CDC.

But local and CDC officials said it's difficult to predict trends based on the numbers. That's partly because of limited experience with the disease, which just hit the United States in 1999, but mostly because the mosquitoes are highly susceptible to weather patterns.

"It's like predicting what the weather's going to be like next year," said CDC spokeswoman Lola Russell. "West Nile virus continues to be a serious mosquito-related disease, and people need to remain vigilant."