Area health officials still don’t really know what caused the 2012 West Nile season to become such a bad one — or why the number of cases dropped so dramatically in 2013.
With that uncertainty, Tarrant, Dallas, Denton and Collin counties are working on a coordinated effort to combat West Nile. It includes year-round trapping and a public awareness campaign urging residents to take more precautions outdoors and around their homes.
“What we’ve learned is it is difficult to predict how bad a West Nile season will be,” said Anita Kurian, associate health director of Tarrant County Public Health.
There’s been some speculation that mild weather may have allowed some infected mosquitoes to survive the 2012-13 winter, but that hasn’t been proved.
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And there’s the confounding information that there were more mosquitoes in 2013 than in 2012, said Zachary Thompson, director of Dallas County Health and Human Services.
“In 2012, there were less mosquitoes but more were infected,” Thompson said. “In 2013, you had an abundance of mosquitoes but fewer were infected.” Some thought it might have to do with the number of infected birds migrating through the area, he said, “but nobody really knows for sure.”
New West Nile definition
In 2012, Texas led the nation in West Nile cases with 1,868, including 89 deaths. The epidemic was at its worst in Dallas County, which recorded 398 cases and 20 deaths, and Tarrant County, which had 280 cases and 11 deaths.
But for some reason, the number of cases plunged in 2013.
Dallas County had 16 cases and two deaths, while Tarrant County had 10 cases and two deaths. Statewide, Texas had 172 cases and 13 deaths, according to the federal Centers for Disease Control and Prevention.
In 2013, there were more cases in California, which had 368, and Colorado, which had 318. California had 15 deaths, and Colorado trailed Texas with seven.
After the 2012 outbreak, Tarrant and Dallas counties began trapping and testing mosquitoes earlier in 2013, and the Denton County Health Department started trapping and testing mosquitoes in unincorporated areas. Collin County adjusted its staffing to better monitor for West Nile.
One new wrinkle this year is that the definition of West Nile is changing, and that may cause a jump in the number of reported cases. A specific fever threshold will no longer be required for classifying a case as West Nile virus if the patient has the other symptoms of the disease.
All four North Texas counties are urging residents to take precautions when they’re outdoors.
“I cannot underscore the importance of using personal protective measures, especially from dusk to dawn,” said Kurian, of Tarrant County Public Health.
Tarrant County has guidelines to help decide when to conduct ground and aerial spraying. Aerial spraying wouldn’t be considered until activity is considered high or an outbreak is in progress.
Tarrant County has contracts for aerial spraying. The cost is $1.87 an acre for aerial spraying and $39.49 per mile for ground spraying. Tarrant County cities can piggyback on those contracts if spraying is needed, Kurian said.
One other concern for health officials is dealing with another mosquito-borne illness at some point in the future.
Chikungunya is an illness caused by a virus that spreads through mosquito bites. The most common symptoms are fever and joint pain, according to the CDC. It has been found on 10 Caribbean islands.
It has not arrived in the United States, but Tarrant and Dallas health officials are worried they might eventually have to deal with it.
“These questions keep coming up about these viruses coming over from the Third World,” Thompson said. “That’s why it’s so important to take precautions with West Nile. We don’t have any human vaccine for West Nile and we need to focus on our senior citizens and those with underlying medical conditions.
“People really need to take responsibility for using insect repellent and cleaning up outside their homes to reduce the mosquito population,” Thompson added.