West Nile on the rise in Dallas, Tarrant counties

The Texas A&M AgriLife Extension Service experts want Texans to be aware of a large rise in mosquitoes testing positive for West Nile virus in Dallas and Tarrant counties.

The state’s warm climate makes Texas a prime breeding ground for vector-borne illnesses, and recent weather conditions have only heightened the mosquito problem for many areas of the state.

“In Texas, our biggest mosquito-related concern is West Nile virus,” said Sonja Swiger, Ph.D., AgriLife Extension veterinary entomologist in Stephenville. “It has been found throughout Texas and the U.S., and even places that don’t normally have a problem like Miami have had cases in 2020. It’s just that kind of a year.”

The West Nile virus also produces symptoms in people that can be similar to some COVID-19 symptoms – fever, cough and sore throat. Anyone experiencing these symptoms should consult their doctor.

“If you think you might have contracted West Nile virus, get tested,” Swiger said. “Do not assume it is COVID-19.”

West Nile mosquito numbers on the rise

“We’re seeing numbers as high in some counties as we experienced in 2012 and that could be problematic,” explained Swiger.

“Tarrant County is currently the hotspot, so to speak, but Dallas County is also starting to see a rise in their number of infected mosquitoes and their vector index,” she said.

“Tarrant County is reporting 30% positive in some areas and 50% positive in the northeast section, which includes the cities of North Arlington, Grapevine, Watauga, Keller and North Richland Hills, to name a few.”

According to Dallas County Health and Human Services, for the week ending Aug.1, 40 mosquito traps tested positive for West Nile Virus. A total of 127 mosquito traps in Dallas County have tested positive to date for the year and there has been one human case reported.

The previous week, Tarrant County reported that 51 trapped groups, or pools, of mosquitoes tested positive for West Nile virus and that there have been 163 positive test pools for 2020 so far.

In 2012, Texas experienced its largest outbreak of West Nile virus in history with over 1,800 confirmed cases.

“Most of these victims reported they were bitten at home,” Swiger said. “So, it’s important that Texans be aware at all times and use repellents when necessary.”

When to worry

AgriLife Extension has identified 85 different species of mosquitoes in Texas, however people don’t need to worry about contracting West Nile disease from all of them – only Culex quinquefasciatus.

Swiger said without any heavy rains, the Culex quinquefasciatus population will continue to grow without chemical intervention.

“We cannot predict what the next few months will bring unfortunately, but if heavy rains are in the future, we would anticipate a decline in positives, as the mosquitoes would be washed away,” she said.

The mosquitoes that carry West Nile virus are night biters, Swiger said. People should be extra cautious when outdoors in the evenings and make sure screens have no holes and doors are kept closed at night and are properly sealed to prevent mosquitoes from entering the home.

Staying safe

“Repellents are a must and the only real way to stay safe,” said Swiger. “Use DEET, picaridin, IR3535 or oil of lemon eucalyptus, which may also be listed as paramenthane-3, 8-diol, on people over 3 years of age, to get adequate protection. These are the only ones tested with certainty to stop the disease-carrying mosquitoes.”

When you are outdoors in any area where there could be mosquitoes, it is wise to wear long sleeves and long pants. The tighter the weave of the fabric, the better protection it will offer from bites.

Hurricanes and mosquitoes

West Nile virus-carrying mosquitoes can be just about anywhere, although we typically see them more around urban areas, said Swiger.

“The recent hurricane to hit south Texas and the lower Rio Grande Valley area has left many areas flooded,” she said. “The rains will kick start development for the many thousands of floodwater mosquito eggs that have been laying dormant in the soil since last year or the last rain event.”

She said when there are large areas of flooding, more locations will be inundated with mosquitoes at the same time.

“When there is just normal rainfall, only isolated areas will spark mosquito development, so hurricanes and tropical storms impact more areas at once and increase populations,” Swiger said. “In addition to the inland floodwater mosquitoes, the salt marsh mosquitoes have been triggered to emerge, and so have any container species that were waiting for water, be that rain or irrigation, to arrive.”

The Rio Grande Valley is not typically a location where we see a lot of West Nile virus, said Swiger, but they are dealing with large populations of mosquitoes right now due to Hurricane Hanna.

Other diseases

It’s not just contracting West Nile from mosquitoes that Texans should be aware of, they are also carriers of viruses such as Zika, malaria and dengue.

Swiger said dengue is the other most important mosquito-related disease Texans need to be aware of.  While it is primarily seen in South Texas, the lower Rio Grande Valley and areas bordering Mexico, someone who contracts it could travel anywhere.

“We also need to remember that Zika is still out there,” Swiger said. “That is something that pregnant women in particular need to be aware of.”

Mosquito basics

Male mosquitos feed only on nectar, unlike their blood-sucking counterparts. Females also feed on nectar but need blood for egg production.

There are species of mosquitoes that feed during the day and species that feed at night. That may be why it seems like there are so many mosquitoes out at dawn and dusk – during these periods, the day and night feeders may overlap.

Swiger said during the day, grassy areas with tree coverage are where mosquitoes like to be to avoid the hot sun. Mosquitoes are cold-blooded and can’t regulate their body temperature. That’s why on warmer days they seek shade and why they typically aren’t around when the thermometer dips below the mid-50s.

“People in the city may not even notice mosquitoes during the day,” she said. “But the species of mosquito that carries West Nile virus typically lives in more urban areas, so people in cities are more likely to contract West Nile virus and need to be aware.”

If you live in the country, you’ll typically encounter more mosquitoes during the day, especially when it’s wet, Swiger said.

“At night, no one is better off than anyone else when it comes to mosquitoes,” Swiger said. “Whether you live in the country, suburbs or a big city, you’ll have mosquitoes to contend with.”

Mosquitoes hibernate in the winter. Some mosquitoes spend their winter as eggs that then hatch when the weather warms up, while others hibernate as adults or larvae. Areas with a hot and humid tropical climate can experience mosquitoes year-round.

Mosquitoes and animals

Mosquitoes can transmit dangerous disease-causing parasites to dogs and horses too, including canine heartworms, Eastern equine encephalitis, EEE, Western equine encephalitis, WEE, and West Nile virus.

“We don’t see Eastern equine encephalitis much, but even one case is cause for concern, since the mortality rate for horses with EEE is 75-80%,” Swiger said. “We typically see cases in East Texas and can expect to have cases in horses again this year. But we haven’t seen a case in humans yet.”

Swiger also noted while there are currently EEE, WEE and West Nile vaccines available for horses, there are none for humans as yet.

Mosquito prevention

The first step in mosquito prevention involves finding and eliminating mosquito breeding grounds. Mosquitoes lay their eggs in or near standing water, so any stagnant water is a potential problem. Any place around the home or property where water can collect and sit for seven to 10 days is a problem to address.

Check property for standing water in clogged rain gutters, birdbaths, old tires, children’s play equipment, potted plant trays, tarps, holes in trees, bowls and buckets — literally anything that can hold standing water. Make sure to regularly change the water in any pet bowls outside.

Dump or drain stagnant water and turn over or cover items that catch and hold water. Gravel or sand can be used to fill places where stagnant water collects.

Mosquito eradication

If a mosquito problem needs wider control, it may be necessary to call a pest control company that specializes in mosquito management. For some do-it-yourself options, AgriLife Extension experts suggest:

– Treating standing water with insecticide/larvicide.

– Applying residual sprays on yard surfaces.

– Using mosquito foggers in the yard.

If opting for a chemical solution, always read the label first and carefully check to determine if it is harmful for human, animals, plants or beneficial insects.

To learn more about mosquitoes, AgriLife Extension offers a Mosquito Control website and a Mosquito Safari. The website also is where Mike Merchant, Ph.D., AgriLife Extension entomologist, Dallas, has created a series of informative mosquito videos. Follow Swiger on her blog for more about bugs and insects.