HOUSTON—Dallas County officials have declared a state of emergency after the West Nile virus infected at least 190 people, killing 10, as the nation’s worst outbreak hits Texas.

An unusually warm winter and rainy spring in the Dallas-Fort Worth area and elsewhere in Texas has provided ideal conditions for breeding mosquitoes, West Nile carriers, officials said.

The emergency declaration in Dallas clears the way for state money and resources to fight the outbreak. In the coming days the county will deploy small planes for aerial insecticide spraying over hard-hit neighborhoods, in addition to ground spraying already underway.

Texans have contracted the highest number of West Nile infections and have suffered more West Nile deaths than any other state in the nation, according to the Centers for Disease Control and Prevention.


Statewide 16 deaths—including the 10 in Dallas County—have been reported so far this year, compared with two in 2011 and seven the year before, according to the Texas Department of State Health Services.

And the virus is spreading at a faster pace this year across the state. As of Monday, 381 West Nile infections had been reported in more than two dozen Texas counties, compared with 27 infections reported statewide last year in a handful of counties.

In Houston alone, about 95% of tested mosquitoes are carrying the virus.

No other state comes close to Texas, according to the CDC. However, neighboring states are also reporting higher infection rates this year: Louisiana and Mississippi each reported 39 West Nile infections and one death. Oklahoma has had 22 infections, but no deaths.


Tarrant County, home to Fort Worth, has reported 171 West Nile infections and two deaths, (compared with two cases last year and no deaths) in what county medical director Dr. Sandra Parker described as “an atypical year.”

“Texas is on track to have the worst year ever for West Nile virus,” Christine Mann, a spokeswoman for the Texas Department of State Health Services, told The Times.

The Lone Star state’s worst West Nile year was 2003, one of the first years the virus was reported to have spread west from Northeastern states. That year, Texas saw 439 West Nile cases and 40 deaths, according to state figures.

Marc Fischer, a CDC medical epidemiologist based in Fort Collins, Colo., told The Times that tracing the roots of West Nile outbreaks is tough.


“It’s a pretty complicated story,” he said, a combination of the right warm, wet weather, mosquitoes, birds (another West Nile carrier) and human behavior.

“Each year we have seasonal outbreaks, and they tend to happen in different places because of those factors,” Fischer said, including recent outbreaks in the Los Angeles area.

Fischer said the CDC expects to release updated state-by-state West Nile surveillance figures Wednesday, and that, “We’re probably hitting the peak nationally.”

“People really should be aware of what they can do to prevent infections—primarily protect themselves from mosquito bites,” he said.


Those infected with West Nile virus may develop West Nile fever, with symptoms such as headache, fatigue, body aches, a skin rash on the trunk of the body and swollen lymph glands. The illness can last a few days to several weeks, according to the CDC.

They may also develop the more serious West Nile encephalitis, meningitis or poliomyelitis, with some of the same symptoms but also neck stiffness, disorientation, tremors, convulsions and muscle weakness that can lead to neurological damage, coma, paralysis and death. The elderly and those with weakened immune systems are most at risk of becoming seriously ill once infected.

Kristy Murray, an infectious disease specialist at Baylor College of Medicine’s National School of Tropical Medicine, told The Times that Texas has seen an uptick in West Nile cases every three years, starting in 2003. It’s not clear why, she said, but ecology plays a role—perhaps all the rain in north Texas after a long-lasting drought.

“Up there it’s prime conditions. Three years ago the hot spot was El Paso. You end up having these hot zones where there’s just a lot of transmission going on,” Murray said.


Murray has been studying Texans infected with West Nile since 2003, and found 90% said they had done nothing to protect themselves from mosquitoes carrying the virus.

“People just become complacent,” she said.

West Nile infections appear to have increased in many states compared with recent years, including California.

California had its first reported West Nile death earlier this month, an 88-year-old woman in Kern County, and 18 West Nile infections reported statewide in eight counties, including one in Los Angeles. That’s almost double the number of West Nile infections reported statewide this time last year. California public health officials already expect this year’s West Nile totals to surpass last year, when the state had 159 infections and nine fatalities.


Nationwide, 241 West Nile infections were reported to the CDC as of the end of July, the most cases reported during that period since 2004.

molly.hennessy-fiske@latimes.com