After ranking as one of the top health stories of 2016, the Zika virus all but disappeared from the headlines once mosquito season came to an end for most of the continental U.S.
But warmer days are coming back. And whether you're bracing for the return of mosquito season here in the states or thinking about heading someplace tropical for spring break, it's important to understand where things stand with this strange and troubling virus.
Here's our quick update on where Zika is spreading now, what we know about the threat it poses to human health, and what you must do to protect yourself:
Is Zika Still Spreading?
The World Health Organization lifted the “public health emergency of international concern” designation for Zika last November. But that status change did not mark the outbreak's end. Between then and January, some 4,000 new cases were reported in just the U.S. and its territories.
Still, the news is not all bad: Although every state in the continental U.S. has reported at least one case of Zika virus infection, Florida and Texas remain the only two states to have suffered local outbreaks (meaning they are the only ones where the virus has been transmitted through local mosquito populations); the remaining states’ cases are all travel-related.
What's more, Florida is no longer an active transmission zone, according to the Centers for Disease Control and Prevention. And although the south-Texas city of Brownsville is still under a travel-advisory issued in late November (when locally acquired infections were first reported there), the rest of Texas remains Zika-free.
There’s good news in Latin America, too. Several countries that struggled to contain outbreaks in 2016 are reporting lower case numbers than expected so far this season, suggesting that mosquito-control efforts are working and/or population immunity is taking hold and dimming the crisis as epidemiologists hoped it would. "The prevalence of Zika is dropping, certainly in the Americas," Ian Clarke, WHO incident manager for Zika, said recently. "The anticipation was that we would see a second wave, certainly in Brazil, and we haven't.”
But this drop in incidence does not mean that we can throw caution to the wind. The WHO and CDC are still urging people—pregnant women, especially—to be very careful about traveling to countries where locally acquired infections have been reported. For a list of these countries, see here.
How to Protect Yourself
For the most part, advice for protecting yourself is 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.
Travelers should wear repellent for at least two weeks after returning because that’s how long the virus stays in a person’s bloodstream. 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.
Travelers should also wait at least six months to have unprotected sex after visiting an endemic region because the virus can persist in semen and in the vaginal tract long after symptoms abate (or even if no symptoms ever emerge).
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 mosquito, because this bug thrives in human habitats and can breed in just a bottle cap’s worth of water.
The Disease and Its Effects
When it comes to Zika infection, scientists are still trying to answer three main questions. The data they have so far is still preliminary, and it will take few more years of monitoring before we have concrete answers. But here's what we know right now:
How likely is it that a fetus exposed to the virus will go on to develop birth defects? Some experts previously put the increased risk at 13 percent. But that was an educated guess based on an isolated outbreak in French Polynesia. More recent data (from Brazil and the U.S.) estimates the risk of microcephaly to be between 3 and 4 percent.
For other birth defects, the numbers are fuzzier. In one recent analysis of Brazilian cases, 42 percent of babies exposed to the virus in utero went on to develop birth defects; but in the U.S. the incidence was much lower. According to data from the U.S. Zika Pregnancy Registry, just 5 percent of babies born to mothers with suspected Zika virus infection went on to develop birth defects, and just 10 percent of babies born to women with confirmed Zika virus infection did.
To be sure, those percentages are not exactly small. As the CDC recently reported, it comes out to a 20- to 30-fold higher risk of microcephaly and other serious birth defects, compared with pre-Zika levels. But the fact remains that far fewer infected fetuses seem to be developing birth defects here compared with Brazil.
Scientists are still trying to understand the reasons for the discrepancy.
What is the scope of birth defects caused by Zika? For most of the epidemic, focus has been on microcephaly, a birth defect characterized by an abnormally small head and a severely under-developed brain. But health officials now suspect that less severe birth defects such as hearing loss, vision loss, and cognitive deficits (some of which can take years to emerge) may be far more common; in one study published recently in the New England Journal of Medicine, just 4 percent of babies infected with Zika in utero were born with microcephaly, but almost 40 percent had other defects.
The CDC has been tracking pregnancy outcomes for infected women through its Zika Pregnancy Registry. If you were infected with the virus during your pregnancy, your doctor may register your case there. The agency will use that information to better understand the types of birth defects that the virus can cause and the relative risk for each.
In the meantime, 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 exhibing 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 importantly—brain imaging studies such as a head ultrasound or CT scan.
How great is the risk to infants and young children? We know that the virus prefers to attack developing neurons (that’s why it’s largely asymptomatic in adults but can wreak havoc on a fetus). But because brain development continues after birth and well into childhood, scientists and parents alike have fretted about the risks posed to newborns and young children.
So far, the news here is good: 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 "works" by disrupting the process of cell division in a developing brain. This process begins in the first trimester of pregnancy and concludes within the first year and a half 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.
Zika's Technology Buzz
Last summer we reported on a number of efforts to thwart Zika through technology. Here's an update on some of the most significant ones:
Zika testing: Scientists have struggled to develop accurate and reliable Zika diagnostic tests. Part of the problem is the virus itself: Zika remains in the blood for only the first few days after infection, and if you don't test during that window (called the viremic stage), you can't be completely sure that a positive result is truly positive.
In December the Food and Drug Administration issued a safety warning to doctors and consumers about one Zika blood test in particular that appears to produce more false positives than expected.
The agency says people who test positive from a doctor-given test must still have their diagnoses confirmed through additional testing at the CDC. That confirmation can take months to arrive, but it's the only way to know for sure if you're infected.
Zika vaccines: The news here is much better. Several vaccines are being tested in Phase I trials right now (Phase I means small groups of human subjects), and at least one has already made it to Phase II (large groups of human subjects), with others expected to catch up this calendar year.
It could still take several years before a Zika vaccine is commercially available. But given how many prospects reached Phase I so quickly, researchers and public health officials are optimistic.
Genetically modified mosquitoes: Last August, the FDA approved a 22-month experimental release of Aedes aegypti mosquitoes that have been engineered to kill off their own population. But in November residents of the Florida Keys issued a split decision: The wider community voted in favor of a proposal from the British company Oxitec to conduct that trial in one of their communities. But Key Haven, where the company had set up shop, voted against that same proposal. Oxitec says it's working with federal regulators to identify a new host community (also in the Florida Keys) and still plans to launch the trial sometime this year.
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