As cases of the dreaded Zika virus spread through Texas, local experts are predicting a bumper crop this month of the mosquito that carries the virus.
Recent rains have assured plentiful breeding habitat for the Aedes mosquito in Central Texas, and Baylor University mosquito researcher Richard Duhrkopf said he expects to see significantly more mosquitoes this year than in summer 2015, which also started off soggy, with Aedes as the most plentiful species.
“We’re nowhere near the peak,” said the associate biology professor who is regional director of the American Mosquito Control Association. “We’re at the bottom of the curve right now. . . . The rains we have had the last few weeks have really stimulated things.”
The Zika virus usually results in mild or no symptoms, but it has been associated in Brazil with a birth defect called microcephaly, which results in small heads. It can be spread by mosquito bites, blood transfusions or sexual contact.
State officials have reported 41 cases of Zika in Texas this year, though none has been the result of mosquito bites received in the U.S. Forty of those, including a pregnant woman, contracted the disease while traveling abroad. The other one, a Dallas County resident, contracted the virus through sex with someone who had contracted it abroad.
No cases have been reported in McLennan or surrounding counties, though Williamson and Ellis counties each had one case.
But local health officials say they are taking precautions to prevent the transmission of the disease.
The Waco-McLennan County Health District has distributed fliers from the U.S. Centers for Disease Control to agencies that deal with pregnant women, with the advice to be cautious about overseas travel, to drain standing rainwater and to use insect repellent. The materials include packets of insect repellent, health district spokeswoman Kelly Craine said.
Craine said physicians, clinics and agencies such as CareNet and Planned Parenthood are in communication with the district about Zika risks. Health care workers pay particular attention to cases in which pregnant women have gone to Zika-infected areas, she said.
“The real risk at this point is travel,” she said.
Dr. Kelley Reynolds, chief medical officer at the Family Health Center, said physicians there are beginning to pass out the information packets to pregnant women and are counseling them on Zika risks. She said immigrant patients who travel are a particular concern.
“We do have a lot of patients who travel back and forth to Mexico,” Reynolds said.
Duhrkopf said he wouldn’t be surprised to see mosquito-transmitted Zika cases in Texas.
“I think it’s quite likely,” he said. “We’re fairly unlikely to see it in Central Texas, but we may see some along the coast, in Houston, Galveston, Corpus Christi or the Rio Grande Valley. . . . We’ve seen some unbelievable amounts of rainfall in Houston, and all that is going to gravitate toward much larger mosquito populations.”
Here and in much of Texas, the dominant mosquito is Aedes albopictus, or Asian tiger mosquito, distinguished by its white “stripes.” It is closely related to Aedes aegypti, which also exists here and has been the vector in tropical Zika outbreaks. Both mosquitoes could carry the virus, Duhrkopf said.
Unlike the Culex mosquito, which carries West Nile virus and is most active at night during hotter, drier parts of the summer, the Asian tiger mosquito feeds during the day, so insect repellent is always a good idea, Duhrkopf said.
But there’s some hope that the feared mosquito-borne Zika epidemic could never arrive in the U.S., Duhrkopf said. It has to do with the transmission pathways of the virus and the habits of the mosquito itself.
Unlike West Nile virus, which is spread by infected birds as well as mosquitoes, Zika is transmitted from human to human through mosquitoes.
Aedes mosquitoes typically spend their entire lives of about one month within about 200 feet of where they were hatched, Duhrkopf said. So the mosquitoes might not be able to carry the virus very far, he said.
“If you’ve got a problem with mosquitoes in your backyard, they’re probably coming from your backyard,” he said. “If we do have transmission of Zika, it’s going to be so localized it’s probably going to be from your backyard or your next-door neighbor’s. One thing we’re hopeful of is that our demographics are sufficiently different enough from those of Rio (de Janeiro) that it becomes a little more difficult to perpetuate. We don’t have a whole lot of people in a given area, and people are not outside a lot.”
Duhrkopf said the Asian tiger mosquito tends to avoid breeding in mud puddles and prefers rainwater collected in buckets, gutters and tarps. They can breed in very small amounts of water, which makes it difficult to get rid of all habitat.
“Source reduction is very difficult to do if it’s trash, like a Starbucks cup that someone has tossed and has blown under a bush,” he said.
Duhrkopf said flooded areas could be breeding grounds for Psorophora ciliata, a large, vicious mosquito. Meanwhile, the Culex mosquito known for West Nile virus prefers stagnant, dirty water, as is often found in storm sewers in the summer. Some of those breeding grounds could have been flushed out by the recent heavy rainfall, Duhrkopf said.