"These babies do not catch up as they grow," says Dr. Antonio Augusto Moura da Silva of the Federal University of Maranhao, Sao Luis, Brazil.
He's describing the findings from a study of 48 babies whose mothers were believed to have been infected with the Zika virus. Forty-two of the children were diagnosed with microcephaly. The study, on the early neurological growth pattern of the infants, will be published in the journal Emerging Infectious Diseases in November but was released early online.
The infants were studied for about four months and up to 8 months of age. Born below average on measures of weight, length and head circumference, they fell even further below average as time passed.
"As they grow, they get worse, and we would expect that they will continue to fall further behind," says da Silva, who was part of the research team. "We were expecting some degree of falling behind average, but we were astonished by the degree to which they were lagging behind."
The Zika virus can pass from pregnant mother to developing fetus. The result can be microcephaly, a birth defect in which the brain does not develop normally and the head is smaller than normal. Other causes of microcephaly include infections during pregnancy with German measles, chickenpox or toxoplasmosis.
Microcephaly caused by Zika was especially cruel to the babies in the study. In those babies, a severe form of disease progressed more rapidly than usually seen in babies with microcephaly due to other causes.
Even when babies exposed to the Zika virus in the uterus are born with normal-size heads, they might suffer other forms of brain damage. In fact, da Silva says, six of the Zika-infected babies in the study did not have microcephaly. And yet, when examined with electroencephalographs to measure brain activity, they showed evidence of brain damage that caused problems including seizures and involuntary muscle movements.
So when there are indications that a mother was exposed to Zika during her pregnancy, screening of the infant should include more than looking for signs of microcephaly, da Silva suggests. "If there is suspicion of Zika infection, you should have a CT scan of the baby to look for lesions of the brain," he says. "Microcephaly does not give the whole picture of this infection."
Most of the mothers of the 48 babies were thought to be infected with Zika during the first trimester of their pregnancy. And because the babies were enrolled at a regional center that assists children with neurological disorders, their symptoms may be among the most severe. Some questions are still unanswered, da Silva says: If an infant is infected after birth, is the virus still able to damage the baby's brain? And what will be the long-term consequences for infants born with less severe cases of microcephaly? "So far, we've studied only the tip of the iceberg," da Silva says.
Still, the findings are valuable, says Dr. James Bale, professor of pediatrics and neurology at the University of Utah who was not part of the study. Until now, medical information about infants born with Zika-caused microcephaly was limited to their appearance at birth. This report provides a look at some short-term consequences of Zika in a handful of infants. "It's a very early snapshot of what these babies are going to look like," says Bale.
What we need next, says Bale, are long-term studies of the full spectrum of infants born to Zika-infected mothers — those babies with severe symptoms and those with milder symptoms. "We don't know anything yet about cognitive outcomes. This paper implies that these babies are going to have difficulties, but we don't know that yet," says Bale. "That takes years to find out."
The study adds to the cumulative information on the catastrophic impact of Zika on developing fetuses, says Dr. Neil Silverman, professor of obstetrics and gynecology at UCLA's School of Medicine and a member of the American Congress of Obstetrics and Gynecology's Zika Expert Work Group. Like Bale, he was not part of the study.
While tests were done to rule out the most common causes of microcephaly other than Zika for the babies in the study, tests to positively confirm that the mothers and babies were infected with Zika were not done. "In an ideal world, we should have pre-delivery testing of the mother," says Silverman. "And at the very least, Zika testing of the babies." Such testing was less readily available when the Brazil study was done than it is now, he says.
What is known for sure is that the children in the study, and others like them, will need lifelong services from specialists including neuropediatricians, ophthalmologists, physiotherapists, nutritionists, nurses and psychologists.