Doctors confirmed the link between the Zika virus and microcephaly in April. While the most visible sign of microcephaly is the small size of the head, its actually inside the brain where the most damage occurs. (Whitney Leaming,Julio Negron/The Washington Post)

The birth defects caused by Zika have been described in heartbreaking detail as the virus has spread to more than 45 countries, infecting hundreds of thousands of people, including tens of thousands of pregnant women. Now researchers have concluded that a Zika infection during pregnancy is linked to a distinct pattern of birth defects that they are officially calling congenital Zika syndrome.

In a report released Thursday in JAMA Pediatrics, researchers from the Centers for Disease Control and Prevention describe five types of birth defects that are either unique to Zika or occur rarely with other infections during pregnancy:

  • Severe microcephaly (abnormally small head size) with partly collapsed skull.
  • Decreased brain tissue with a specific pattern of calcium deposits indicating brain damage.
  • Damage to the back of the eye with a specific pattern of scarring and increased pigment.
  • Joints with limited range of motion, such as clubfoot.
  • Too much muscle tone, restricting movement soon after birth.

Researchers at the CDC, along with colleagues elsewhere in the United States and Brazil, analyzed publicly available reports about defects among infants and fetuses whose mothers had either confirmed or presumed infection with Zika virus during pregnancy. Most of the clinical descriptions of Zika-affected infants are from Brazil, the heart of the epidemic.

The most common timing of infection that led to birth defects is late first and early second trimester, although third-trimester infections were also reported among infants with birth defects.

The five features described in the report are an initial list of clinical findings. It’s becoming increasingly clear, however, that the full spectrum of health problems caused by a Zika infection won’t be known for months and even years after birth.

At a conference in September on Zika’s effect on children, sponsored by the National Institute of Child Health and Human Development, researchers described an array of problems associated with Zika exposure beyond microcephaly, mostly stemming from the virus’s harm to the nervous system.

Children born to Zika-infected mothers will need to be regularly monitored because some problems don't show up until months later, said Catherine Spong, an obstetrician-gynecologist and the institute’s acting director.

“Although the severe cases are teaching us a lot, the impact is likely much more broad, and these impacts, although less striking, may be much more widespread and may need more monitoring and interventions,” she said.


These images show the different types of damage caused by congenital Zika infection. (JAMA Pediatrics/Cynthia A. Moore, J. Erin Staples, et. al)

Researchers say the purpose of the latest report is to describe what is known about the congenital syndrome. The description is intended to help health-care providers “better recognize the pattern of birth defects associated with congenital Zika virus infection,” said Cynthia Moore, a clinical geneticist and birth-defects expert for the CDC and lead author of the report.

Doing that will help providers evaluate and coordinate care for affected babies and their families, she said.

At least 1,005 pregnant women have Zika infections in the 50 states and the District of Columbia; 25 U.S. infants have been born with Zika-related birth defects and an additional five pregnancies are known to have resulted in miscarriage, stillbirths or terminations with evidence of birth defects.

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