In the middle of West Nile Virus season in Texas, the virus remains unpredictable as ever

There are still two months left in the traditional West Nile Virus season in North Texas, and longtime mosquito control expert Patrick Prather can’t tell you what will happen next.

“The ability to predict West Nile Virus season is a tough one to nail down,” said Prather, the executive director of Municipal Mosquito, which provides virus surveillance and mosquito control for dozens of North Texas cities and counties.

So far this year, there have been eight cases of West Nile Virus detected in humans in Texas, according to state data from July 29. In Dallas County, one woman has died after being diagnosed with West Nile neuroinvasive disease , the most serious form of the disease. Tarrant County public health officials reported that a 70-year-old Fort Worth resident was diagnosed with the neuroinvasive disease last month.

West Nile Virus spread is so unpredictable that it’s hard to compare year to year, said Dr. Scott Weaver, the director of the Institute for Human Infections and Immunity at UT Medical Branch at Galveston.

“Nobody can predict very well when there’s going to be a less active year versus a more active year,” Weaver said.

But despite the challenge of pinning down West Nile Virus, it remains the most common diseases spread by mosquitoes, ticks, or fleas in Texas. The virus spreads to humans through mosquitoes, who in turn get infected by biting birds. The infected mosquitoes then carry the virus to humans and other animals, Weaver said. The virus does not spread from person to person.

For most people, getting bitten by a mosquito that carries the virus is not an issue: Nine out of 10 people who get infected do not report any symptoms or illness, according to the U.S. Centers for Disease Control and Prevention. But a small minority of those infected will develop symptoms, and, in vary rare occasions, the virus can affect the central nervous system and cause death.

The most active year in recent memory was 2012, when an outbreak infected more than 1,800 people in Texas. About half of those infections were in the Dallas-Fort Worth area. More than 800 people developed West Nile neuroinvasive disease, the most serious outcome of the virus, and 89 died, according to researchers who studied the outbreak.

That outbreak is what spurred the virus surveillance and management system that exists in North Texas today, Prather said. The system remains a patchwork, and cities and counties have different protocols for how they look for the virus, if they look at all, and how they eradicate infected mosquito populations if the virus is detected.

In Arlington, for example, staffers put out mosquito traps throughout the city, said Aimee Rockhill, the city’s health services manager. Samples will then be sent to Tarrant County Public Health’s laboratory, where they will be tested for the virus. If the mosquito pool test positive for the virus, city staff will use a non-toxic larvicide in the area where the virus-positive mosquitoes were identified, Rockhill said. Arlington staff also proactively search for mosquito larvae throughout the city, and dump any standing water where they find them, she said.

Other cities and counties have different protocols for detecting and surveying mosquitoes, Prather said. Check with your local municipality to determine how it detects and responds to West Nile Virus in mosquito pools.

How to protect yourself

Although the spread of the virus changes from year to year, Texans are always at risk because the virus is endemic to the state, meaning it spreads locally among birds and moquitoes.

“You can never say there’s no West Nile, because it’s here all the time,” said Rockhill, who is a registered environmental health specialist and registered sanitarian.

West Nile Virus is most dangerous in people 60 and older, Weaver said, so people in those age groups should take particular care to avoid mosquito bites during the summer months.

Wearing long loose fitting clothing and mosquito repellent can help prevent getting bitten, he added.

Rockhill urged residents to dump any pooled water on their properties and to avoid overwatering their lawns or gardens.

Some municipalities, including Burleson, offer free larvicide to residents who want to try and control the mosquito population on their property.