City monitors infected mosquitoes

Posted Monday, Jul. 01, 2013  comments  Print Reprints
More information Symptoms West Nile Fever: People who contract this milder form of the ailment often experience headache, muscle and joint ache, fever, nausea and fatigue, but generally recover on their own within a few weeks. West Nile Neuroinvasive Disease: This is the more dangerous variety, causing symptoms such as stiff neck, stupor, disorientation, coma, tremors, convulsions, muscle weakness and paralysis. There is no specific treatment for West Nile. Controlling Spread Regularly drain standing water, including water collecting in empty cans, tires, buckets, clogged rain gutters and saucers under potted plants. Mosquitoes that spread WNV can breed in as little as a tablespoon of stagnant water. Use an approved insect repellent. Among the EPA-approved repellents are those that contain DEET, picaridin, IR3535 or oil of lemon eucalyptus. Wear long-sleeve shirts and long pants outdoors at dawn and dusk when mosquitoes are most active. Source: Tarrant County Public Health Department. For more about the West Nile virus and strategies to combat it, visit the health agency’s website at and click on West Nile icons.

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It’s summer time, and Howard Redfearn’s seasonal job – keeping the West Nile virus out of Mansfield – is heating up.

Redfearn, the city’s year-round storm water manager, started mosquito trapping in mid-April – two months earlier than last year -- and, so far, so good. No infected mosquitoes have been snared yet in the six sample sites around the city.

But the potentially debilitating virus has begun turning up in mosquitoes in other parts of Tarrant County. The first human case of infection this year, reported June 14, was a Fort Worth woman in her 40s, according to the Tarrant County Public Health Department, which coordinates mosquito collection, testing and spraying in cities and unincorporated areas.

The woman contracted a milder version of the virus, commonly called West Nile Fever.

Saturday night, trucks sprayed in two rural areas just east of Eagle Mountain Lake, based on rapid increase in the number of the types of mosquitoes that carry the virus.

“Last year Mansfield had nine human cases, plus three sample locations that had a positive mosquito,” Redfearn said. “Everybody had a lot last year.”

In 2012, Tarrant County reported its first human case June 20, nearly a week later than the first case this year. Last year, there were 280 people infected with the West Nile virus in the county. Eleven of those died, the agency reported.

The virus is transmitted to humans by mosquitoes, which contract it from birds that have been infected by mosquitoes.

This year the county is directing a new approach to help predict where mosquito populations will grow, which would allow for spraying even before the first West Nile-positive mosquitoes turn up. That could reduce the number of infected birds and help slow the spread of the virus, Redfearn said.

“(Health officials) have mathematical models that will show when we’ve gotten in a risk zone based on the number of mosquitoes,” he said.

This year, health officials are requesting that traps remain stationary and be checked once a week. Previously, many mosquito traps were routinely moved from site to site during collection season. Mansfield had been rotating three traps among 12 collection sites each week, meaning each site was monitored for one week per month.

This year, Mansfield put out five stationary traps. A sixth trap “we’re rotating to fill in the gaps within the city,” Redfearn said.

Now, with each site being checked every week, the county over the next few years can develop a more useable database for its projections.

“What we’re trying to get away from is waiting until we start seeing West Nile-positive mosquitoes or getting confirmed human cases” before taking action, Redfearn said. “To get better data, you need to get a better idea of what the mosquito population is doing.”

The residency of infected people, including the nine of Mansfield, provides little help, he said.

“That’s the whole rub. We have no way of knowing if those people were infected by mosquitoes in Mansfield,” he said. “People go watch their kids play soccer, and a lot of people who work in Mansfield live someplace else.”

Redfearn urged people to use insect repellent and remove stagnant water, where mosquitoes lay their eggs, and to know the symptoms of infection.

“Like anything else,” he said, “the earlier doctors can intervene, the better outcome you can have.”

Robert Cadwallader, 817-390-7641 Twitter: @Kaddmann

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