Zika Virus May Affect Infants Even Without Microcephaly and Cause Tissue Death, Studies Find

— -- Researchers are learning more about the Zika virus and how it affects the development of infants in utero -- and what they're learning is painting a grim portrait of the destructive nature of the infection for the fetus.

Two studies published today in the medical journal the Lancet shed new light on the effects of the virus.

In one study, researchers from multiple institutions, including the Brazilian Ministry of Health, examined children who had been born to mothers with suspected Zika virus infections. The virus has been found to cause microcephaly, a birth defect characterized by an abnormally small head. However, researchers found of the approximately 1,500 births they studied, about 20 percent of the babies born with Zika virus had normal head circumferences. This means these infants may have developmental delays or other defects even though they do not have microcephaly.

The other study published by researchers from multiple institutions, including the National Center for Emerging and Zoonotic Infectious Diseases at the U.S. Centers for Disease Control and Prevention, examined the ways the virus affects brain tissue. They looked at brains of three infants who died after being born with Zika-related microcephaly and also at fetal tissue from two pregnancies that ended in miscarriage related to Zika infection.

By looking at the tissue, researchers found evidence of body deformities, cell death and abnormal calcium deposits in brain tissue related to the viral infection.

The researchers hope to be able to better understand how the virus attacks the developing brain through these studies.

Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical Center, told ABC News that the study findings show how much researchers are playing catch-up with this disease.

"I’m afraid the more we learn the nastier the Zika virus is," Schaffner said. "It’s quite evident that the Zika virus, if it gets into a pregnant woman, can get into the placenta and into the baby and it gets right into the brain cells."

Schaffner said other birth defects, including those that affect sight and hearing, often appear if brain development is affected in utero.

"Some of the babies will have blindness and hearing defects," if their brain development is impacted, Schaffner explained. "Some of the babies who appear normal at birth on follow-up can be found tragically later to have limitations of brain function, vision and hearing."