Expert Commentary

Zika virus and birth defects in Brazil: New research

2016 study published in The New England Journal of Medicine that investigates the link between Zika infection and fetal abnormalities, including microcephaly, in Brazil.


Scientists are still trying to gain a better understanding of the Zika virus–which the World Health Organization has called an international public health emergency–while public health officials scramble to manage outbreaks without a complete scientific picture of the disease.

Zika is transmitted by mosquitoes and usually causes mild symptoms such as fever, joint pain and red eyes, according to the U.S. Centers for Disease Control and Prevention. However, new studies have linked the disease to devastating birth defects.

For example, a March 2016 study published in the Journal of American Medical Association reports that Brazil saw a 20-fold increase in cases of suspected microcephaly—a disease which results in an abnormally small head in newborns—from 2010 through 2014, or  nearly 4000 cases in 2015. The study notes that evidence of the virus has been found in the placenta and amniotic fluid of mothers and in the brains of fetuses or newborns. Yet a causal relationship between Zika virus and microcephaly has not been established.

New findings offer the first look into how Zika might be harming developing brains and fetuses. A March 2016 study, “Zika Virus Infection in Pregnant Women in Rio de Janeiro—Preliminary Report,” published in the New England Journal of Medicine  followed 88 pregnant women patients in Rio de Janeiro, Brazil from September 2015 through February 2016. Of the women, 72 (88 percent) tested positive for Zika in blood, urine or both.

The study’s findings include:

  • Although microcephaly has been a focus of concern for Zika infection in Brazil, the study noted that other fetal development problems were frequently found: 29 percent of ultrasonogram tests showed growth restriction, damage to the central nervous system, weakened placenta and death.
  • The damage to the fetus was the same regardless of whether the mother exhibited mild or severe symptoms of the virus. In other words, only 28 percent of the women had a fever, one of the symptoms of Zika, so screening for the virus based on the presence of fever would miss 70 percent of the cases.
  • Zika infection can cause some of the same birth defects as rubella—which was responsible for a U.S. pandemic in the early 1960s before it was eradicated by a vaccine—such as microcephaly and other types of brain malformations and central nervous system problems. But rubella causes problems only in the first half of pregnancy whereas Zika-infected women experience these problems in later stages of gestation too.
  • Researchers contrasted their findings on pregnancy problems experienced by women infected with Zika to those of woman infected by HIV who had taken part in a prior study. They noted the results were alarming: Over a period of the few months that the Zika study took place, the fetal death rate was 4.8 percent—nearly twice the rate, 2.5 percent, for the HIV-infected group which had been followed for nearly a decade.

Given the risk of abnormal fetal development and death, women with suspected or confirmed Zika infection should be monitored closely, with scheduled ultrasound tests, according to the study’s authors. The study cautions, “despite mild clinical outcomes, Zika infection during pregnancy appears to be associated with grave outcomes, including fetal death.”

Related research: A 2016 study, “The Emerging Zika Pandemic: Enhancing Preparedness,” examines what steps need to be taken against the further spread of Zika, including vector control, health information campaigns, travel advisories for people traveling to Zika-infected areas and accelerated research and development on vaccines. A 2014 study published in the Journal of the Royal Society Interface, “Global Rise in Human Infectious Disease Outbreaks,” offers a general look at infectious disease outbreaks between 1980 and 2013.


Keywords: microcephaly, infectious disease, epidemics, pandemics, outbreaks

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