Zika virus causes different types of brain damage in babies, not just microcephaly, according to two new reports.
Brazilian researchers found as many as one in five babies born with brain damage caused by Zika had normal-sized heads. That means babies who may seem normal may in fact suffer from serious conditions that parents and doctors may not notice until they get older.
The findings show that if a pregnant woman is infected with Zika — even if a baby is born with a normal-sized head — the child could have severe brain damage.
Worse, the study confirms that many of the pregnant women whose babies were affected didn't have the obvious symptoms of Zika, such as a rash. The virus is known to cause invisible infections in most people who catch it — usually good news, but that's bad news for pregnant women who may not know anything is amiss until their babies start showing symptoms as they grow.
And the study also found that even late in pregnancy, babies can suffer brain damage caused by Zika. In other words, there's no stage of pregnancy that's safe.
More than 7,000 suspected cases of Zika brain damage have been reported in Brazil, where Zika started spreading fast more than a year ago. In the U.S., the Centers for Disease Control and Prevention knows about 287 pregnant women infected with Zika -- all via travel -- plus another 250 in U.S. territories such as Puerto Rico. Of these, seven have been born with defects and six have died, miscarried or been aborted.
Dr. Cesar Victora of the Federal University of Pelotas in Rio Grande do Sul, Brazil, looked at 602 newborn babies suspected of having been affected by Zika.
"About one in five definite or probable cases had head circumferences in the normal range," they wrote in their report, published in the Lancet medical journal.
That suggests that many babies may have been part of Brazil's Zika epidemic but their doctors and parents may not yet know. "The finding of several newborn babies with neuroimaging abnormalities despite normal sized heads suggests that the initial focus on microcephaly was too narrow," they wrote.
Other studies have shown that Zika homes in on developing brain and nerve cells and doctors feared babies who seemed fine at first in fact would have brain damage caused by Zika. This study confirms it's true.
Other studies have also shown that Zika causes far more symptoms than microcephaly alone. Babies born to moms infected with Zika can have vision and hearing problems and other disorders that depend on just what part of the brain the virus has damaged.
Zika targets brain and nerve cells. The Brazilian team's finding confirms this happens throughout pregnancy.
"As expected, the earlier the rash occurred during pregnancy, the smaller was the mean head circumference at birth, suggesting a causal association," they wrote.
"Rashes in the third trimester of pregnancy were associated with brain abnormalities despite normal-sized heads," they added.
"Among Zika virus affected pregnancies, some fetuses will have brain abnormalities and microcephaly, others will have abnormalities with normal head sizes, and presumably others will not be affected."
Another recent study found that while Zika usually clears up within two weeks at the longest, pregnant female monkeys could be infected for as long as two months. Doctors suspect the same thing may happen in pregnant women and if that's the case, the virus could affect a developing baby all during the time, as well.
And, Victora's team said, newborn babies may be at risk, also.
In another report in Lancet, Dr. Sherif Zaki of the Centers for Disease Control and Prevention and colleagues examined three Zika-affected babies who died after they were born, and the placenta from two babies who miscarried.
They found Zika caused many different types of brain damage as well as limb and genital malformations. The two women who miscarried were infected early in pregnancy, and lost the pregnancies soon after, they said.