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After ranking as one of the top health stories of 2016, the Zika virus has all but disappeared from the headlines.
But, out of the spotlight, scientists studying Zika have learned more about the nature of how this virus spreads, how it affects people exposed to it, how to prevent it, and where people are still at risk.
Here’s what you need to know about these developments.
Where Is Zika Still a Problem?
Right now, the Centers for Disease Control and Prevention (CDC) rates the continental U.S., including Florida and Texas, as areas with no known risk of Zika infection. (Zika virus transmission has never been recorded in Hawaii or Alaska.)
So far in 2019, officials know of no one in the 50 U.S. states who’s gotten Zika from a mosquito bite they received inside the country, and they’ve recorded just one person who brought the disease back to California after acquiring it in another country. That’s down from 72 travelers who acquired the disease internationally during 2018.
The situation is improving in Puerto Rico as well. In 2019, the island reported 147 cases of Zika picked up from local mosquitoes; so far in 2019, no cases of the disease have been reported in Puerto Rico or any other U.S. territories.
But Zika remains a potential threat. Currently, the CDC says that no country is experiencing an active outbreak, but that doesn't mean there’s no risk of picking up the disease.
The World Health Organization and CDC are still urging people to exercise caution and use insect repellent when traveling to countries that have reported locally acquired infections. And the CDC says pregnant women should talk to a healthcare provider about potential risks before traveling anywhere locally acquired infections have been reported at any time, even if there has not been any recent transmission. (The CDC maintains a list of these countries.)
How Should You Protect Yourself?
The advice for protecting yourself is basically the same as it has been throughout the global Zika outbreak: Avoid traveling to affected regions, especially if you are or are trying to become pregnant. If you live in an affected region or must travel to one, wear insect repellent that has been registered with the Environmental Protection Agency. (See our insect repellent ratings.)
Travelers who go to a country with an outbreak should wear repellent for at least two weeks after returning because that’s how long the virus stays in a person’s bloodstream. This helps protect your community once you return home, a key part of preventing locally acquired infections. If a mosquito bites a person who has Zika in their blood, that mosquito can pick up the virus and pass it on to another human when it takes its next blood meal.
People living in or near affected communities should practice integrated pest management around their homes. Ridding your yard of standing water (removing old tires, planters, and other water collectors) and keeping it free of trash is particularly important for diseases like Zika that are transmitted by the Aedes aegypti mosquito, because this bug thrives in human habitats and can breed in just a bottle cap’s worth of water.
This is good practice if you live somewhere that mosquitoes are common, even if Zika isn't a concern. Late last year, for instance, Miami-Dade county warned that it had confirmed one case of Dengue transmitted by a local mosquito.
What Precautions Should You Take If Exposed?
Last year, CDC released a report on preventing sexual transmission of Zika. There was one major change in the advice.
Previously, officials had said that men who were possibly exposed to Zika should wait six months before having unprotected sex or trying to conceive a child. Now, the CDC says men can shorten that wait time to three months. (The CDC defines possible Zika exposure as traveling to or living in an area where Zika is a risk, or having unprotected sex with someone who lives in or recently traveled to an area where Zika is a risk.)
“We have learned more about the persistence of Zika in different types of body fluids, including semen,” says Peggy Honein, Ph.D., M.P.H., the CDC’s director of the division of congenital and developmental disorders, and an author of the report. “Emerging data suggests that the infectious virus is there [in semen] for a shorter period of time.”
If a possibly exposed man’s partner is pregnant, however, Honein says that as an additional precaution for protecting a developing fetus, “we recommend that throughout the duration of pregnancy, the couples either use condoms or abstain from sex.”
The CDC’s advice to women remains the same: If it’s possible you’ve been exposed to Zika, wait two months before having unprotected sex or trying to conceive.
Pregnant Women and Zika
Scientists are making progress on better understanding Zika infections, but there’s a lot we still don’t understand. To that end, the CDC has been monitoring thousands of children born to mothers who had a confirmed or suspected case of Zika while pregnant. This data has shed light on two key questions:
How Likely Is it That a Fetus Exposed to the Virus Will Develop Birth Defects?
A recent study looked at 1,450 of those children, for whom researchers had medical records of follow-up care and who were at least a year old by February 2018.
The scientists found that among these children, the rate of birth defects associated with Zika, including microcephaly (a birth defect characterized by an abnormally small head and a severely underdeveloped brain) was 6 percent. In other words, among 100 pregnant women with Zika, six of their babies had Zika-related birth defects.
That rate is 30 times as high as the rate at which those same birth defects occurred in the general population in the pre-Zika era. This finding tracks with what other research have found, according to Honein, who worked on the study.
What Is the Scope of Birth Defects and Other Problems Caused by Zika in Pregnant Women?
For most of the epidemic, the focus has been on microcephaly.
A recent finding from the CDC’s data on Zika-exposed pregnancies calculates the rate of other problems, however—not birth defects, but what the CDC calls “neurodevelopmental abnormalities,” which emerge in the months and years after birth. These could include seizures, problems with moving or swallowing, hearing or visual impairment, learning disabilities, and more. Nine percent of the children studied had one of these problems.
In children with these issues, the problems weren’t always immediately identifiable, Honein says. “Most of them looked healthy at birth.” Included in this category, for example, are cases of microcephaly that developed over time, after head circumference measurements were normal at birth.
Because of the risk of health problems that may emerge months or years after birth, the CDC advises that any babies born to women who showed some evidence of Zika infection during pregnancy (either through confirmed diagnosis, or by virtue of exhibiting symptoms after returning from a Zika-affected region) have comprehensive testing done throughout the first few years of life to monitor for developmental delays. That testing includes newborn hearing tests, physical exams, and—most important—brain imaging studies such as a head ultrasound or CT scan. The CDC offers a full set of guidelines for follow-up care.
“If all of these recommendations are followed, we should be able to identify any problems these children are having early,” Honein says.
What About Babies and Children Who Are Exposed to Zika?
One piece of good news: There have been very few reports of serious health problems among newborns and toddlers bitten by Zika-infected mosquitoes.
In fact, the vast majority of children who test positive for the virus are asymptomatic, just like adults.
Scientists have an idea about why this might be the case: The Zika virus harms developing brains by disrupting the process of cell division. That process begins in the first three months of pregnancy and ends within the first 18 months of life. After that, they think, the risk of brain damage may be far lower because there are fewer dividing brain cells for the virus to act on.
Where's the Zika Vaccine?
There’s not yet a vaccine approved for protection against the Zika virus. But plenty of scientists and drug companies are working on developing one. The National Institutes of Health, for instance, is currently conducting a Phase 1 trial (meaning a small number of human test volunteers are trying the vaccine out for safety, rather than efficacy).
And that’s just one of several Zika experiments listed on the government’s clinical trial registry that are either underway or recruiting volunteers. Jodie Dionne-Odom, M.D., assistant professor of medicine and infectious disease at the University of Alabama at Birmingham School of Medicine, compares it to a race, with many companies working at the same time with the same goal.
It could still take several years before a Zika vaccine is commercially available. But given how many prospects are already being tested in humans, researchers and public health officials are optimistic. One review of vaccine efforts published last year in the journal NPJ Vaccines called the progress “spectacular.”
Still, one potential problem with a Zika vaccine, notes Dionne-Odom, is that given Zika’s effects on developing fetuses, the vaccine will need to be approved for use in pregnant women. And that means it must clear a higher safety bar than a vaccine being tested for the general population. “That has to be carefully thought out and carefully considered from a safety perspective,” she says.
But Dionne-Odom expects that once a viable vaccine is approved for the general population, scientists will try to speed the approval process for pregnant women as well.
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