It’s early, but concern is growing that 2017 could be another bad year for the West Nile virus.

Tarrant County saw its earliest positive West Nile sample earlier this month in Grapevine, and the city did ground spraying on April 13.

It was the earliest positive pool since testing began following the 2012 West Nile outbreak. Last year’s first positive Tarrant County sample occurred May 6 in Arlington.

But early samples do not neccesarily translate into a lengthy West Nile season.

“It’s difficult to predict how the season is going to turn out this early,” said Anita Kurian, associate director at Tarrant County Public Health.

There are a number factors that come into play.

Only one mosquito pool has tested positive in Tarrant County and it was a culex restuans mosquito, which can overwinter in Texas. The primary vector for West Nile transmission to humans in Texas comes from the culex quinquefasciatus.

“We’re are cautiously optimistic because we haven’t seen a positive in the Culex quinqs,” Kurian said.

But Joon Lee, an associate professor of biostatistics and epidemiology at the University of North Texas Health Science Center in Fort Worth, said the early positive sample is a cause for concern. With the help of his students, he traps and tests for West Nile at 62 locations across Fort Worth.

“Detection of West Nile virus in the mosquito population in April indicates that a sizable amount of the virus transmission has already started in bird populations and the virus transmission to humans will start early,” said Lee. “Thus, it is reasonable to expect that there will be more human West Nile virus cases.”

Rain a factor

Weather conditions can play an important role.

The right kind of rainfall can help wash away mosquito pools while hot, dry weather can help fuel mosquito breeding.

“If you have heavy rainfall that goes on for days, it’s a good natural way of preventing large mosquito pools,” Kurian said. “But if you have a small amount of precipitation that’s not prolonged over a long period of time, you can have standing water that helps mosquitoes breed more easily.”

Officials are hoping to avoid a repeat of 2012 when Texas led the nation for the year with 1,868 West Nile cases, including 89 deaths. That year, Tarrant County saw 280 cases and 11 deaths.

Last year, Tarrant County had two West Nile deaths. There were 44 human cases — 28 cases were the more serious neuroinvasive, plus 16 that were West Nile fever.

A Tarrant County death in January also was connected to West Nile. Gary Curtiss Copeland of Keller, 71, died three months after being bitten by a mosquito. His cause of death was bacterial pneumonia, with West Nile virus as an underlying cause, according to his death certificate.

Dallas County is preparing for the possibility of another difficult year.

Ground spraying has already taken place in two Mesquite ZIP codes and one Balch Springs ZIP code after mosquito traps tested positive for West Nile. Last year, Dallas County had 61 West Nile cases and three deaths.

Worried about Zika

Zachary Thompson, Dallas County Health and Human Services director, is just as concerned about the Zika virus. While many think it is unlikely to get established in North Texas, Thompson said there is still much to be learned.

Six locally transmitted cases of the Zika virus were found in Cameron County last year near the Texas-Mexico border. More than 260 cases have been reported in South Florida, according to the Miami Herald.

“The lesson learned from Cameron County and Florida is if you do find one localized transmission, there’s going to be other local Zika cases, too,” Thompson said.

While many humans who contract the Zika virus show no symptoms, it can be devastating for pregnant women.

A Centers for Disease Control and Prevention report released earlier this month said 1 in 10 pregnant women in the U.S. who were confirmed to have Zika last year had a fetus or baby with a brain abnormality or other neurological disorder.

The Texas Department of State Health Service issued a health alert in early April that recommends all pregnant residents of Cameron, Hidalgo, Starr, Webb, Willacy and Zapata counties be tested in both the first and second trimesters of pregnancy.

Testing is also recommended for any residents from those counties who have a rash and any of the other common Zika symptoms — fever, joint pain or eye redness.

Zika is carried by the Aedes aegypti mosquito, which can also transmit dengue fever. Health officials hope dengue provides a roadmap for how Zika will act in Texas.

This year, Tarrant County will be trapping for aedes aegypti to monitor the prevalence and numbers, but not testing for Zika unless officials start seeing local transmission.

There has been local transmission of dengue fever in South Texas but only isolated cases in the rest of the state.

So far, Tarrant County has had 27 travel-related cases of Zika, but no local transmission has been reported.