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    Here's What You Need To Know About the Zika Virus and Microcephaly

    The experts say to be aware, not afraid.

    The World Health Organization just declared a public health emergency over the Zika virus.

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    In the past weeks there have been countless headlines warning people of a new disease spreading to America, coupled with shocking images of its suspected victims: babies born with "shrunken heads." Pregnant women have been warned against traveling to affected countries, and the world has started to panic over the threat of a pandemic straight from a sci-fi film. But what is actually happening to these babies?

    BuzzFeed Health spoke to two experts on pregnancy and public health, Alix Casler, M.D., pediatrician at Orlando Health Physicians Associates, and Robert Amler, M.D., Dean and Professor of public health, pediatrics, and environmental health science at New York Medical College, to find out.

    1. First, some background: Zika is a mosquito-borne virus that's become an epidemic in Brazil and other parts of Central and South America.

    Centers for Disease Control (CDC) / Via

    Zika has been around since 1947, when it was found in Uganda. Up until 2015, outbreaks mostly occurred in Africa, Southeast Asia, and the Pacific Islands. In May 2015, the Pan American Health Organization (PAHO) confirmed the first outbreak in Brazil, and outbreaks are now occurring in 22 other countries in Central and South America — and the CDC reports that 31 travel-acquired cases have been confirmed in the United States. It is estimated that 3 to 4 million people in the Americas could become infected with Zika in the next year.

    The Zika virus is transmitted to people primarily through infected mosquitos in tropical regions. "It's a mild infection — 80% of people have no symptoms but the 20% who do get a fever, rash, and joint pain for one week," Amler says. There is no vaccine, and the only treatment is rest and hydration. During the first week of infection, the Zika virus is detectable in the blood and it can passed from the infected person to a new mosquito — but after about one week, the virus is out of your system, Amler says.

    2. So why the emphasis on pregnant women? The Zika epidemic in Brazil coincides with a rise in reported cases of microcephaly, a birth defect some people call "shrunken head syndrome."

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    "There has been an alarmingly high number of children born with brain damage associated with microcephaly in Brazil," says Casler. And according to the CDC, in rare cases the Zika infection can be spread from mother to newborn during birth.

    The CDC also reported that higher number of people than usual in Brazil have Guillain-Barré syndrome, a rare autoimmune disorder that can lead to paralysis. However, the link between Zika and Guillain-Barré is only a potential connection and requires further investigation.

    3. Health officials suspect that there's a link between the Zika virus in pregnant women and microcephaly.

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    According to reports from the CDC, the increased reports of microcephaly from congenital infections in Zika virus–affected babies suggests a possible relationship, but additional studies are needed to confirm an association. "It's a circumstantial link because these two things are occurring at the same time — but it is not very clear whether the virus alone is causing the birth defect or not," Casler says. Besides, Zika has been around since the last century and has been infecting people, including pregnant women, for decades, says Casler. But pregnant women in affected regions do seem to be at high risk.

    4. Microcephaly is a condition where a baby's head is abnormally small.

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    A baby is diagnosed with microcephaly when the head circumference is more than two standard deviations below the mean size (or in the third percentile) for sex and gestational age at birth. The top of the head appears very small and disproportionate to the body, says Casler. For this reason, many people still refer to the condition as "shrunken head syndrome."

    5. It occurs when the brain doesn't develop properly in the womb or if it stops growing after birth.

    Center for Disease Control / Via

    Since a baby's head grows as the brain grows, Casler says, microcephaly occurs when the brain fails to keep developing at some point in the pregnancy — or in some cases if the brain stops growing as a newborn. "It's not only that the head is small, the brain is damaged and it has little lumps called calcifications, which impairs the ability to move," says Amler.

    6. Microcephaly can have a range of devastating health effects, depending on how severely the brain is damaged.

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    Microcephaly causes cognitive and intellectual impairment, and the resulting disabilities can range from learning disabilities to significant developmental delays that can affect motor and speech, says Casler. It can also cause seizure disorders and sensory issues such as loss of vision and hearing. "It's impossible to grow up normally and it can have devastating effects on a family," says Amler.

    7. The cause of microcephaly in most babies is unknown, but most cases are due to genetics.

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    "We do not know the specific mechanism which causes the brain to stop growing or when exactly this happens in the pregnancy," says Amler. However, there are certain risk factors such as genetic conditions, malnutrition, and certain infections or chemical exposures during pregnancy.

    8. Infections such as rubella and toxoplasmosis (when they occur during pregnancy) may also cause congenital microcephaly.

    Bullit Marquez / AP / Via

    "There are infections where we absolutely know that the baby is at high risk for brain damage," Casler says. Rubella (also called German measles) can manifest as a mild infection in the mother but is usually asymptomatic, though there's at least a 20% chance it will cause microcephaly, mental retardation, cataracts, and deafness in the baby. Other infections such as toxoplasmosisis from cat litter and cytomegalovirus (CMV) also cause severe impairment to the brain.

    "The fetus is very vulnerable to infection because the body tissues are still developing and forming organs, so if there's a disruption in the process you can get terrible malformations, which we see as birth defects," Amler says. We usually prevent rubella with vaccinations and other infections or exposures can be avoided by the mother if she is aware and careful during her pregnancy.

    9. That said, we still don't know how likely microcephaly is in babies born to women who had the Zika virus.

    Felipe Dana / AP / Via

    The statistical risk is still unknown because the population of pregnant women infected with Zika and the number of women who gave birth to babies with congenital microcephaly is unknown. "We need to know how many infections it takes for one baby to be injured — one microcephalic baby out of 1 million moms who had Zika is extremely different from one in 500," says Casler. The WHO, CDC, and ministries of health in affected countries are all working to increase surveillance and update registries for Zika and microcephalic babies. However, it is difficult to report Zika infections during pregnancy retroactively, after the baby is born, because the virus is usually asymptomatic and many women are unable to recall if they had an infection.

    10. The good news is that the number of confirmed cases of microcephaly in Brazil is much smaller than originally thought.

    Felipe Dana / AP / Via

    The birth prevalence of microcephaly in Brazil during the second half of 2015 alone was over 10 times higher than the historical prevalence. However, the CDC reports that the protocol for reporting cases and the registry itself increased that number. As of Jan. 23, the actual confirmed rate is much lower than originally thought.

    Brazil's Ministry of Health reported 3,448 suspected cases of microcephaly, and so far only 270 have been confirmed, with 17 testing positive for Zika; 462 of the cases involving brain damage have been ruled out. But since testing for Zika is still difficult and time-consuming, there are about 3,000 cases of microcephaly that just haven't yet been verified. "Researchers are still collecting data on Zika and microcephaly to prove a causation and understand the infection timing," says Casler.

    11. And evidence has shown that Zika does not affect later pregnancies, and it's safe to conceive two weeks after an infection.

    Andre Penner / AP / Via

    "As far as we can tell, having Zika does not influence later pregnancies, and if you're infected it is safe to conceive in two weeks because the virus has left the body within about a week," says Amler. However, both experts recommend that people stay updated and alert, because there is new data emerging and reports are coming out every single week.

    12. The best strategy is to be aware, not afraid.

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    Health officials are responding to the outbreaks by reporting all cases to a national registry, removing breeding areas and treating infected water sources, and issuing travel warnings for pregnant women. The CDC has issued guidelines for all mothers and infants possibly infected with Zika. The CDC has issued an alert for people traveling to 14 countries in Latin America with special precautions for pregnant women. "The best prevention for women in endemic areas is wearing long sleeves and pants, using EPA-approved insect repellant, staying indoors, and sleeping with a mosquito net," says Amler.

    "Focus on self-care, not fear," says Casler. "It's not a definite risk, but it's uncertain, so you should protect yourself as best you can by avoiding travel or taking all those precautions seriously." Pregnant women who do have any symptoms of Zika (fever, rash, joint pain) or plan to travel should meet with their health care provider so they have the best chance of having a healthy baby.

    It's important to stay alert and educated by reading the most recent updates on Zika from reputable sources. Click on the sources below for more information:

    — Center for Disease Control (CDC)

    World Health Organization (WHO)

    Pan American Health Organization (PAHO)