While the population of mosquitoes in Lewisville is declining, it’s still mosquito season, and human cases of the West Nile virus in Texas continue to increase.
“We have less positive traps this year than last year, but West Nile virus is a serious illness,” said Chris McGinn, the city’s Health and Animal Services manager.
When we spoke to McGinn Aug. 8, he said the Centers for Disease Control had 18 reported human cases of the disease in Texas. As of Aug. 14, there have been 21 reported cases. There has been one death in the state from West Nile this year.
West Nile virus is most commonly spread through infected mosquitoes. It can cause febrile illness with symptoms such as fever, joint pain or diarrhea. It can also cause neurologic illness, or inflammation of the brain, the lining of the brain or the spinal cord, and can cause symptoms such as disorientation, paralysis, tremors or coma.
The risk of infection is highest for those who work or are frequently outside, but anyone living in a locale with infected mosquitoes can get it, according to the CDC. People with compromised immune systems are at a higher risk of severe illness.
Lewisville has had 15 West Nile-positive mosquito traps so far this season. There have not been any reported human cases in the area, and the City of Lewisville does what it can to respond as quickly as possible to positive tests and mosquito complaints.
Each week, Vector Disease Control International, which contracts with the city, sets out mosquito traps at nine locations throughout Lewisville. The following day, the traps are collected.
Lab technician Elena Ilieva said she uses tweezers to sort mosquitoes by species and gender. The mosquitoes are then tested to see whether or not they are carrying the West Nile virus.
The Culex species can carry West Nile and are more active from the evening into the morning. The Aedes aegypti and Aedes albopictus are primarily more active during the day time and are carriers of chikungunya, dengue and Zika.
“Typically we catch much more of the others than the Zika carriers,” Ilieva said.
Gailyn Cook, shop manager for Vector Disease Control, said the company starts setting traps April 1 and keeps doing so through Thanksgiving.
“The traps vary — anywhere from 15 as high as 1,000 mosquitoes in each trap,” Cook said.
Reports are sent to city staff over the weekend. If local mosquitoes test positive, city staff alerts residents through media releases, an update on the city website and a call-out on Monday that insecticide spraying will commence the following Tuesday and Wednesday.
Because the insecticide kills adult mosquitoes, a follow-up day of spraying after the initial spraying is necessary to get the majority of the mosquitoes, McGinn said.
“If you have mosquitoes that are in the larval stage, you may have a second round of mosquitoes hatch after you’ve already sprayed the night before,” he said.
The city has response measures for preventing mosquito breeding, halting larva from becoming adults and extinguishing as much of the existing mosquito population as possible.
“We want to only spray or fog if a public health threat exists, meaning yes there’s going to be mosquitoes. There’s always going to be breeding sites,” McGinn said.
McGinn said there’s a decrease in positive traps this year compared to 2016. The week of July 30, there were about 50 positive traps in Texas, while the same week a year ago yielded 150 positive traps. The week before that there were 90 positive traps, but in 2016 there were 120.
The most important thing that can be done is to educate the public, McGinn said. If he had to tell residents to do one thing, it would be to drain standing water on their property on a routine basis.
“Sometimes mosquito–laid eggs can last up to two years in dry conditions,” he said. “When somebody’s dumping standing water on their property, they want to make sure they scrub the container with a brush to knock those eggs off, otherwise those eggs are still there.”
Go to ltjne.ws/mosquitotips for more information on how to prevent contracting West Nile. Contact Chris McGinn at 972-219-3484 to report any mosquito complaints in Lewisville.
Editor’s note: This story has been updated to reflect the current findings of West Nile- positive test samples.