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  • Blue Ocean l 16-06-22 00:00:00 l View : 748
  • Science Magazine June 2016

    Experts fear Zika's effects may

    be even worse than thought

    Doctors and researchers are scrambling to define “Zika congenital syndrome”

    By Gretchen Vogel

     

    Zika keeps unveiling menacing new talents. For many years the virus was thought to cause only mild symptoms. Then, in July 2015 doctors in northeast Brazil noticed a spike in cases of microcephaly, or unusually small heads, showing up in ultrasound examinations of pregnant women. Many of the women reported having had a fever or the rash typical of Zika infection, which had started spreading in the region a few months earlier. In April, the U.S. Centers for Disease Control and Prevention concluded that Zika virus causes this brain defect, which can result in developmental and learning disabilities. Now, case reports make it increasingly clear that babies infected in utero also have problems in their eyes, ears, limbs, and perhaps other organs.

    “It seems there are a broader range of effects that go beyond microcephaly,” says Tarun Dua, who is helping cooordinate the response to Zika at the World Health Organization (WHO) in Geneva, Switzerland. Earlier this month WHO announced that it is launching an effort to characterize what doctors are now calling Zika congenital syndrome. “We are looking at many thousands of babies, and we need a systematic process for defining their symptoms,” Dua says.

    Animal- and cell-based studies have shown that Zika virus readily infects the cells of the nervous system, which would explain most of the symptoms identified so far. “We've been learning very bad things on a weekly basis,” says Paolo Zanotto, a virologist at the University of São Paulo in Brazil. He notes that the damage is so extensive in some cases that the skull has filled mostly with fluid, and “there is no brain.” Those babies die shortly after birth. Other infants may have only mild brain damage that will not be apparent until learning disabilities or other problems show up years later.

    Doctors focusing on microcephaly may miss significant problems. On 7 June, doctors in Recife, Brazil, reported in The Lancet that they had diagnosed brain damage and scars on the retina of a 2-month-old baby that did not have microcephaly but did have limb spasms shortly after it was born. A brain scan revealed significant defects, including ventricles that were larger than normal and brain tissue that was smoother than it should be. The mother reported no symptoms of Zika infection during pregnancy. However, further tests showed that the baby had antibodies to the virus in its cerebrospinal fluid, strong evidence that it was infected before birth.

    Several cases suggest that the damage may go well beyond the nervous system, says Pilar Ramón-Pardo, coordinator for Zika emergency response at the Pan American Health Organization in Washington, D.C. Doctors in Panama and Colombia are reporting that a handful of mothers who had Zika symptoms during pregnancy have given birth to children with problems in the heart, digestive system, and genitals, Ramón-Pardo says. “We need to investigate whether those cases are related to Zika” or have some other cause.

    In July, WHO will gather about 50 clinicians and researchers in Recife to draw up a preliminary definition of Zika congenital syndrome. The participants will also develop guidelines for the tests that doctors should use, both at birth and during several years of follow-up, to try to capture the full spectrum of problems the virus might cause, Ramón-Pardo says. The work should help countries better understand what kinds of treatment and support affected children and their families will need, Dua says.

    One continuing challenge is the difficulty of diagnosing Zika itself. Symptoms are often mild, or even absent, and a blood test is accurate for only a few days after infection. Previous infections with dengue virus, very common across Latin America, can cloud results on antibody tests, the standard for detecting past infections in people who have already recovered. And many symptoms can have multiple causes. For example, microcephaly can be caused by genetic disorders, alcohol or drug exposure, and infections such as cytomegalovirus, toxoplasmosis, and syphilis.

    To try to get a clearer picture of the risk for pregnant women and their babies, researchers have started several prospective studies, enrolling thousands of women in areas where Zika is circulating. The researchers plan to test the women regularly for infection and then follow them and their babies for at least 2 years. Such studies “will provide some information, but it is going to take some time,” Dua says.

    In the meantime, there is a glimmer of good news from the Recife region. A few months ago, Manoel Sarno, a fetal medicine doctor at the Federal University of Bahia in Salvador, says he saw as many as 10 cases of microcephaly per week. He now sees only about one a month. That may only reflect a seasonal drop in Zika infections during last year's dry season, but there are other signs that the outbreak in the region is receding. It's possible, he says, that so many people were infected last year that the population's “herd immunity” is high enough to stop the virus's spread—and make Zika congenital syndrome a rare occurrence in the region.