County is reporting first death from West Nile Virus

Denton County Public Health (DCPH) is reporting the second human case and the first death of West Nile Virus (WNV) in Denton County this year. This newly reported case is the second in Denton County and resided in the northwest quadrant of unincorporated Denton County. This individual is also the first WNV-related death and was diagnosed with West Nile Neuroinvasive Disease. You can see her obituary on page 2.  “We’re seeing more positive mosquito traps in the last few weeks indicating increasing risk for contracting West Nile Virus, just as we’ve seen in our second human case and first death of the season,” stated Juan Rodriguez, DCPH Assistant Director and Chief Epidemiologist. “We ask community members to take preventive actions to lower their risk of contracting a mosquito-borne illness.”

Why is there an increase in positive mosquito traps this year?

West Nile virus is the most common mosquito-borne disease in the U.S. Cases are more prevalent when mosquito populations swell under the right environmental conditions.

Temperature and rainfall can have a significant impact on mosquito populations, said Vanessa Macias, a University of North Texas professor with expertise in mosquito biology.

Denton County has had significantly more rainfall so far this year compared to last year, according to the National Weather Service.

“The more rain we have, the more mosquitoes we’re going to have,” Macias said.

As a result, Denton County alone has announced it was taking action to cull mosquito populations on 15 occasions so far in 2024, compared to three occasions in 2023.

What is being done to address West Nile virus?

Denton County places mosquito traps in high population density areas of the county’s jurisdiction. It tests these traps weekly from May to October.

Cities in Denton County also regularly test mosquito traps for the virus, including the City of Sanger.  

Cities within the county and Denton County itself have been conducting ground fogging in their respective jurisdictions each time a trap yields a positive test result.

When ground fogging is done, it’s conducted three times in the area. It doesn’t have to be consecutively but close in time, said Jenica Bates, DCPH’s public information officer. So, it could occur three days in a row or three times within a week.

Ground fogging employs a fine mist of insecticide and water. When dispersed, the mist can kill adult mosquitoes on contact.

Killing adult mosquitoes is the best way to eradicate diseases like West Nile virus, Macias said.

Mosquitoes are different from other disease-transmitting insects, Macias said, in that they have to ingest the virus and the virus has to reproduce inside the mosquito first to be transmitted.

“So, it infects the mosquito truly,” Macias said. “Once the virus has infected the mosquito and gotten into her salivary glands, the next time she bites someone, she’ll spit the virus into them. So, the virus actually needs the mosquito in order to be transmitted. That’s really important, because that means if we get rid of the mosquito in an area, then we won’t have the virus.”

However, it’s possible that ground fogging will not kill every mosquito in an area.

Additionally, mosquito populations can grow quickly. Their typical lifespan, from egg to adulthood, is about two weeks, Macias said.

So, ground fogging is a temporary solution. However, Macias conducts research into a more permanent solution to eradicate mosquito-borne diseases: genetic engineering.

“You give mosquitoes a small set of new genes that enable them to do something new,” Macias said. “What we’re interested in giving them is either genes that cause them to essentially self-destruct, so it causes a population crash, or genes that help them to recognize a specific pathogen like West Nile so that when they inject the virus, they can recognize it and destroy it instead of passing it on to another human or bird.”

The genetically engineered mosquitoes would breed with others, passing the genes through a population.

It’s much easier to build the population crash genes in a laboratory, Macias said. That solution, Macias said, is being deployed in Brazil to reduce dengue fever and being tested in other places with promising results.

How can you avoid contracting West Nile virus?

Because there are no vaccines or medications to cure West Nile virus, the best way to prevent it is by protecting against mosquito bites.

Mosquitoes will bite during the day or at night. However, they are most active at dusk and dawn. Local authorities recommend staying indoors at these times.

When outside, use insect repellent containing 10% to 30% DEET, wear long-sleeved shirts and pants, and eliminate mosquito breeding grounds.

Mosquitoes breed in standing and stagnant water. Prevent such water from accumulating in yards and neighborhoods.

Some common neighborhood mosquito sources are:

Uncovered boats

Open trash bins

Clogged rain gutters

Fountains and bird baths

Potted plant saucers

Buckets and barrels

Pet water bowls

Wagons or other toys

Areas beneath leaky hoses

Neglected pools

Tires

Rot holes in trees

Ponds

Low ground areas

It’s important to check and clean these areas regularly, Bates said, because new mosquitoes could breed and hatch quickly after water accumulates.

Residents should avoid even the smallest accumulations of water if possible.

“Mosquitoes can lay their eggs and grow in very small quantities of water,” Macias said. “So, even if we’re proactive in getting rid of standing water, there’s always little pockets of water they can find.”

For standing water that can’t be dumped, Bates recommends using Bti briquettes, also known by the brand name Mosquito Dunks.

These contain a larvicide that releases a natural bacterium called Bacillus thuringiensis israelensis (Bti) that can kill mosquito larvae before they mature.

Please visit the DCPH West Nile Virus website at DentonCounty.gov/WNV for additional information including mosquito maps, latest news, and facts about WNV.