Zika-linked abnormalities that occur in human foetuses are more extensive and severe than previously thought, according to scientists who found that microcephaly is not the most common congenital defect caused by the infection.
The study suggests that damage during foetal development from the mosquito-borne virus can occur throughout pregnancy and that other birth defects are more common than microcephaly, when babies are born with very small heads.
These defects may only be detected weeks or months after the baby is born, said Karin Nielsen, a professor at University of California, Los Angeles (UCLA).
“This means that microcephaly is not the most common congenital defect from the Zika virus,” Nielsen said. The absence of that condition does not mean the baby will be free of birth defects, because there are problems that are not apparent at birth and such difficulties may not be evident until the age of six months, she said.
The results are a follow-up to a smaller study that used molecular testing to find an association between Zika infection in pregnant women and a series of serious outcomes that included foetal deaths, abnormal foetal growth and damage to the central nervous system.
This is the largest study to date of Zika-affected pregnancies in which the women were followed from the time they were infected to the end of their pregnancies.
All the women were enrolled before any abnormalities in their pregnancies had been identified. The study was based 345 women in Brazil, who were enrolled from September 2015 through May 2016.
Of those women, 182, or 53 per cent, tested positive for Zika in the blood, urine or both.
In addition, 42 per cent of the women who did not have Zika were found to be infected with chikungunya, another mosquito-borne virus; three per cent of Zika-positive women also had chikungunya.
From there, the researchers evaluated 125 women infected with Zika and 61 who were not infected with the virus who had given birth by July 2016.
The previous study was based mainly on prenatal ultrasound findings; by contrast, the current research evaluated infants from Zika-affected pregnancies through physical examination and brain imaging.
Researchers found that there were nine foetal deaths among women with Zika infection during pregnancy, five of those in the first trimester.
Foetal deaths or abnormalities in the infants were present in 46 percent of Zika-positive women, contrasted with 11.5 percent of Zika-negative women.
Forty-two per cent of infants born to the Zika-infected mothers were found to have microcephaly, brain lesions or brain calcifications seen in imaging studies, lesions in the retina, deafness, feeding difficulties and other complications. The study was published in the New England Journal of Medicine.