Some Experts Question Extent of Zika Threat to U.S.

By Dennis Thompson
HealthDay Reporter

THURSDAY, May 26, 2016 (HealthDay News) — Are health officials in the United States overreacting to the threat posed by the Zika virus this summer?

Some leading insect and infectious-diseases experts think so, arguing that the mosquito-borne virus is unlikely to become a widespread hazard to pregnant women throughout the United States.

“I think the risk for Zika actually setting up transmission cycles that become established in the continental U.S. is near zero,” said Chris Barker, a mosquito-borne virus researcher at the University of California, Davis School of Veterinary Medicine.

He said Zika should follow a pattern similar to other tropical diseases spread by mosquito bites, such as dengue fever and chikungunya, which have failed to gain any significant foothold in the United States.

“We do a pretty good job of shielding ourselves from mosquito bites in this country, with our screening and air conditioning. That seems to be enough to limit the risk for dengue, and we think the same will be true for Zika,” Barker said.

If that proves true, then small Zika outbreaks could occur in southern states where the breeds of mosquito that carry these diseases are most active, Barker and other experts said.

Zika virus is frightening because it’s the first mosquito-borne illness known to cause a brain-related birth defect — in this case microcephaly — if an expectant mother becomes infected.

Microcephaly results in babies born with abnormally small heads and brains. Nearly 5,000 babies have been born with microcephaly in Brazil, the epicenter of the Zika epidemic, according to the World Health Organization.

Given the threat to pregnant women and their fetuses, the U.S. Centers for Disease Control and Prevention has chosen to err on the side of caution in its Zika response, said agency spokesman Tom Skinner.

“The bottom line is that no one can predict with absolute certainty what’s going to happen here in the United States when it comes to local transmission of Zika virus,” Skinner said. “Many areas in the U.S. have the type of mosquitoes that can transmit this virus. We just can’t predict with any absolute certainty what’s going to happen.”

At the same time, federal health officials know that some parts of the United States are more vulnerable than others, he said.

“Based on what we’ve seen in years past with dengue and chikungunya, we certainly wouldn’t be surprised to see Zika emerge in an area like Florida or Texas or somewhere along the Gulf Coast or the Mexico border,” Skinner said. “While those areas are likely to be a priority, we want to make sure that other states — where we know these mosquitoes can possibly transmit the virus — are prepared to the extent they can be prepared.”

To limit any potential spread of Zika, health officials on the federal, state and local levels are deploying a three-pronged strategy: improving mosquito control; expanding their ability to test for Zika; and urging the public to protect themselves against mosquitoes.

However, officials acknowledge it won’t be possible to test every woman who’s pregnant or might become pregnant to see if she has been infected with the virus. That’s why self-protection and mosquito control are critical components of the Zika strategy, officials say.

Gulf Coast states like Florida, Louisiana and Texas are most at risk for local Zika outbreaks as this year’s mosquito season progresses, agreed Dr. Amesh Adalja, a senior associate at the University of Pittsburgh’s UPMC Center for Health Security in Baltimore.

The reason: those are the states in which Aedes aegypti and Aedes albopictus mosquitoes “are abundant and/or in which Aedes-spread diseases such as dengue and chikungunya have had local transmission,” Adalja said.

The Aedes mosquitoes can range farther north, but it’s highly unlikely that they’ll flourish enough to carry Zika into more northern states, said Laura Harrington, chair of entomology at Cornell University in Ithaca, N.Y.

“Here in New York state, there’s been a lot of pressure placed on mosquito-control districts to do as much as they can. And, they’re really strapped for resources, and there’s not a huge risk of transmission compared to a place like Florida,” Harrington said.

Much of the national concern stems from maps released recently by the CDC showing that the Aedes mosquitoes can range as far north as New York, Ohio, Kansas, Missouri and California, she said.

“They’re showing this mosquito in places where there’s no way you’re going to find them,” Harrington said. “It’s really unfortunate, because it’s causing a lot of hysteria in places where people should be focusing on other health issues, like Lyme disease.”

All three experts — Barker, Adalja and Harrington — agreed that Zika requires a strong public health response, but it needs to be focused on the southern states most at risk.

“Those are the places that should have more resources,” Harrington said.

Florida is the state in the continental United States that warrants the most concern regarding Zika, with Texas close behind, Barker said.

“They have high travel volumes to places where Zika is transmitted regularly, and lots of travelers returning,” he said, referring to Latin America and the Caribbean. “We don’t have evidence for local transmission in those places (Gulf Coast states) at this point, but people should be aware the possibility exists.”

At the same time, Barker said people shouldn’t alter any travel plans within the United States based on concerns over Zika.

“We are starting to see people wondering whether they should take vacations to places like Georgia or Louisiana. And, I think the answer is to be aware of the risks that mosquito bites pose, but I wouldn’t be canceling vacations to most U.S. states at this point,” he said.

So what can women who are pregnant or planning to become pregnant do to protect themselves and their fetuses from mosquito bites? They should wear long-sleeved shirts and long pants, use mosquito repellent when outside, and stay indoors as much as possible.

These women should also use condoms or refrain from sex with a male partner if they are living in an active Zika area.

And people can cut their local risk by eliminating mosquito habitats from their property. Get rid of any source of standing water — such as buckets, plastic covers, toys or old tires. Empty and change the water in birdbaths, fountains, wading pools and potted plants once a week. Also, drain or fill with dirt any temporary pools of water, and keep swimming pool water treated and circulating, according to the CDC.

More information

For more on Zika virus, visit the U.S. Centers for Disease Control and Prevention.

This Q&A will tell you what you need to know about Zika.