With mosquito season arriving in the Gulf Coast states, U.S. public health officials have begun deploying a three-pronged battle plan to combat Zika virus, which has caused thousands of birth defects in Latin America in the last year.
Zika is the first mosquito-borne illness known to cause birth defects, U.S. Centers for Disease Control and Prevention Director Dr. Tom Frieden has reported. While the virus typically prompts either mild or no symptoms in nearly all adults, it can inflict terrible brain-related birth defects if a pregnant woman becomes infected.
Brazil has been the epicenter of the Zika outbreak with nearly 5,000 confirmed or suspected cases of microcephaly, which causes babies to be born with abnormally small heads and brains.
The virus is expected to become active in at least some portions of the continental United States this spring and summer, especially Gulf Coast states, as it passes from person to person via mosquito bites, federal health officials say.
Health experts are hopeful that Zika will not spread as widely in the United States as it has in Central and South America. The main reasons: people aren’t as exposed to mosquitoes in the United States, and much of the nation’s climate isn’t as tropical as Latin America’s.
“The fact that we have more access to screens and air conditioning by itself is probably very highly protective,” Dr. John Hellerstedt, commissioner of the Texas Department of State Health Services, said during a recent Zika seminar.
To limit any potential spread of Zika, health officials on the federal, state and local level 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.
Each state has a good idea which of its regions is more likely to have the Aedes aegypti mosquito, the main carrier of Zika, said Dr. Frank Welch. He is medical director of the Louisiana Department of Health and Hospitals’ Center for Community Preparedness.
For example, Louisiana officials are first directing their attention toward the Lake Pontchartrain area near New Orleans, along with some other smaller pockets around the state, Welch said.
“By really focusing on the neighborhoods where we know this mosquito is active, we really hope to head off local transmission,” he said.
Florida has included 17 counties in a Declaration of Public Health Emergency regarding Zika, according to the Florida Department of Health. The counties are scattered throughout the state.
“We’re working to make sure that all Florida residents and visitors are informed about Zika virus and mosquito-borne illness in general,” said Mara Gambineri, a spokeswoman for the Florida Department of Health.
In Texas, public health officials are keeping an eye on the Lower Rio Grande Valley, the Gulf Coast, and particularly the Texas/Mexico border, Hellerstedt said.
Zika has become active in some parts of Mexico, and there is concern people could carry the virus across the border into the United States.
“All along that border every day, hundreds of thousands of people legally cross over from one side to the other and return,” Hellerstedt said. “That is their way of life. That’s the basic socioeconomic reality of those communities.”
In a similar vein, Louisiana health officials are keeping a keen eye on cruise ships returning from Central and South America, Welch said.
People disembarking from cruise ships are warned that they may have been exposed to Zika, he said, and that they could inadvertently start local transmission of the virus if a mosquito bites them and then spreads the virus to other people.
“We are confident that Zika is returning to Louisiana every day among travelers,” Welch said.
Mosquito control key to containing the virus
Mosquito control will play a pivotal role in preventing the spread of Zika. But, it’s not likely that pesticides will do much good. The A. aegypti mosquito has developed strong and varied resistance to insecticides, Frieden said, and what works in one place will likely not work in another.
Frieden recently visited a lab in Puerto Rico where they were testing the effectiveness of pesticides against local mosquitoes. The island territory has had nearly 700 confirmed cases of Zika and one death linked to the virus.
“Unfortunately in Puerto Rico, many of the pyrethroid insecticides met with a high degree of resistance,” Frieden said. “So I saw very effective insecticides with mosquitoes flying happily around an hour later; it doesn’t affect it whatsoever. And then with at least one of the insecticides, mosquitoes were knocked down within 15 minutes.”
As a result, the public will have to take an active role in mosquito control if people want to prevent active Zika transmission, Welch and Hellerstedt said.
The A. aegypti mosquito feeds exclusively on humans, and often breeds in small pools of water near homes and communities rather than in ponds or swamps, Hellerstedt said. The mosquito particularly prefers close-quartered urban areas, where there are many people from which to feed.
People will need to regularly police their homes, backyards and neighborhoods, eliminating any sources of standing water, Welch said. This could become tedious, since every new rain shower will bring fresh pools of standing water in flower pots, lawn furniture and the like — but it must be done.
“If we reduce the incidence of this mosquito breeding in everybody’s yard, garden and neighborhood, we will reduce the risk of establishing local transmission of the Zika virus,” Welch said.
Tests are ready to check for infections, but they aren’t fool-proof
Much of the public health response to Zika will depend on doctors’ ability to test patients for the virus, and some officials are concerned that a wave of infections could overwhelm state and federal laboratories.
There currently are two approved lab tests for Zika, according to the CDC:
- One is the PCR test, which tests for Zika by looking for the virus’ genetic material in a person’s bloodstream.
- The other test, called the MAC-ELISA, examines a person’s blood for Zika antibodies. These antibodies show that a person has been infected with Zika and has developed the antibodies to fight off the virus.
The only way health officials will be able to tell if Zika has become active in a community is by testing people for the virus, Welch and Hellerstedt said.
“Our ability to do surveillance is going to be largely dependent on our ability to identify Zika disease in human beings, and not in mosquitoes,” Hellerstedt said.
Officials can trap and test mosquitoes for Zika, but “it’s not as useful as you might imagine,” he said. “If you went out and trapped 100 mosquitoes in a given area, you have no way of knowing the 101st and all the other 10,000 mosquitoes in that area don’t have it as well.”
The PCR test is easy to produce and administer, and health departments across the nation are arming themselves with it, the CDC says. At least 44 of the more than 150 labs in the CDC’s national Laboratory Response Network now have the ability to perform PCR tests for Zika, according to agency officials.
On top of that, the FDA recently granted emergency authorization for the national private company Quest Diagnostics to perform PCR testing. The company plans to charge $500 for each test, or $120 for people who lack health insurance, said Dr. Rick Pesano, Quest Diagnostics’ vice president of research and development.
Pesano said his company will help health officials keep up with demand for Zika testing, relieving the “stress and strain of having these tests done in a timely manner.”
However, the PCR test has one major drawback — it can only detect an active Zika infection, and people usually clear the virus from their bloodstream within a week, Pesano said.
“That will help some, but it probably won’t by itself solve our testing problem,” Hellerstedt said of Quest’s contribution.
Pregnant women who are worried they’ve been infected with Zika will need the MAC-ELISA test, which can show whether they have ever had the virus. But even that test has drawbacks, Hellerstedt noted. It’s tougher to administer, slower to produce results, and not as accurate as might be hoped, he said.
A woman who’s been infected with another virus in the same “family” as Zika — dengue or chikungunya, for example — would receive a positive result from the MAC-ELISA, Hellerstedt said. Blood with any positive result would then need to be forwarded to the CDC for even more rigorous testing before a woman would know whether her pregnancy truly is at risk.
Given this, “it won’t be possible to test every pregnant woman if we have to do so over a very broad area,” Hellerstedt said.
Frieden said CDC lab workers are testing new innovations that could cut the one-week confirmation time for the MAC-ELISA down to three or four days, but added that his lab’s ability to increase production will depend on future funding.
The Obama administration has asked Congress to allocate $1.9 billion to combat the Zika threat, but the lawmakers have yet to act on the request.
“The bottom line is, without significantly increased resources, it’s going to be very difficult to do the kind of innovations that provide rapid testing and rapid control,” Frieden said.
In the meantime, women of child-bearing age who live in areas where Zika transmission is occurring can protect themselves from mosquito bites by wearing long-sleeved shirts and long pants, using mosquito repellent when outside, and staying indoors as much as possible, health officials advise.
And women should use condoms or refrain from sex with a male partner if they’re living in an active Zika area. They should also follow these precautions for at least eight weeks if the man has traveled to an active Zika area, or for at least six months if the man has been diagnosed with Zika.
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.