Women infected with the Zika virus late in their pregnancies had babies with no apparent birth defects, a study has found.
The greatest risk to infants comes from infection early in pregnancy, the research seems to confirm.
However, the study found troubling cases of severe birth defects in babies born to women who never realised they had contracted Zika – and had no symptoms.
Commenting on the findings, experts today warned pregnant women: ‘You’re not out of the woods if you don’t have symptoms’.
Women infected with the Zika late in their pregnancy had babies with no apparent birth defects, a study found
Ever since a Zika virus outbreak in Brazil was linked to severe birth defects late last year, health experts have been trying to understand when developing foetuses are most vulnerable.
They were also seeking to find out whether foetuses are at risk if the mother is infected but never experiences symptoms.
The Colombian researchers tracked 1,850 pregnant women with Zika. They knew which trimester these mothers-to-be had become infected.
Of the 600 women infected during their third trimester, 90 per cent have delivered their babies, and none gave birth to a child with microcephaly or other obvious birth defects, researchers found.
Women MUST delay pregnancy in Zika-ravaged countries: WHO…
Revealed, the areas of Europe where Zika is most likely to…
Mother is told she has cervical cancer while GIVING BIRTH:…
More than a QUARTER of pregnant women light up in Blackpool:…
The Zika virus is spread mainly through the bite of a tropical mosquito, the Aedes Aegypti – but can also be spread sexually as the virus can live for months in semen.
And studies showing Zika can also survive in saliva raised concerns the virus could be passed through kissing or sharing cutlery or toothbrushes with people who are infected.
Most people with the virus never develop symptoms. Others get a fever, rash, joint pain, or red eyes, and recover within a week.
There is no vaccine so in outbreak areas, the main defense is to avoid mosquito bites.
Brazil, which has suffered the largest outbreak of Zika, has had more than 500 cases of Zika-linked microcephaly, a severe birth defect in which a baby’s skull is much smaller than expected because the brain hasn’t developed properly.
Severe birth defects were seen in babies born to women who didn’t know they had Zika and never experienced symptoms. Pictured is a baby with microcephaly – a birth defect linked with Zika
Experts have been watching to see if the epidemic would play out in Colombia, Brazil’s northern neighbor, in similar fashion.
The study’s authors call the report ‘preliminary’ as most of the women followed by researchers were still pregnant at the time the report was completed.
Researchers want to track both the pregnancies and the children who have already been born, said one of the study’s authors, Margaret Honein, of the Centers for Disease Control and Prevention.
WOMEN MUST DELAY PREGNANCY IN ZIKA-RAVAGED COUNTRIES: WHO SAYS IT IS THE ONLY WAY TO AVOID DEVASTATING BIRTH DEFECTS
Women who live in areas where Zika is spreading should consider delaying pregnancy, leading health experts urged.
The World Health Organization issued the advice as it said there is no certain way to avoid the devastating birth defects caused by the virus.
It echoes advice already given by several countries where the virus is in widespread transmission.
The warning came just weeks after officials said sexual transmission of the virus is more common than first believed.
Zika is primarily transmitted by the Aedes aegypti mosquito, but research shows it can also be transmitted sexually – and possibly through saliva from kissing or sharing cutlery.
The agency released a correction to its guidance for preventing sexual transmission of Zika to clarify the difference between people who live in the Zika-affected areas and people who visit them.
‘In order to prevent adverse pregnancy and foetal outcomes, men and women of reproductive age, living in areas where local transmission of Zika virus is known to occur, be correctly informed and oriented to consider delaying pregnancy,’ it said.
It’s possible that the babies who have been born and appear not to have any defects may still develop problems, she said.
And Colombian officials have only been reporting on live births.
They have not said how many Zika-affected pregnancies developed birth defects but ended in stillbirth, miscarriage or abortion.
It’s not surprising that infections later in pregnancy did not lead to apparent defects, because Zika and other viral infections early in pregnancy are more likely to cause defects like microcephaly, said Dr Neil Silverman, a UCLA professor of obstetrics who has been advising the California Department of Public Health on Zika issues.
He said the total number of defects out of Colombia appear to be surprisingly low, however.
Colombia saw only four confirmed Zika-related microcephaly cases between August and April, when the study was conducted. Two more have been reported since then.
The researchers don’t know at what trimester the mothers of the four microcephaly cases were, because none of the women experienced symptoms, Ms Honein said.
That means that while it is unlikely, a third trimester infection could not be completely ruled out in each of those cases.
It also ‘really heightens’ the concern that even women who don’t feel sick can pass a Zika infection to their babies, and the babies can develop defects, Ms Honein said.
‘You’re not out of the woods if you don’t have symptoms,’ said Dr Ian Lipkin, a Columbia University infectious diseases expert who was not involved in the research.
Most Zika-caused birth defects have been reported in mothers who said they developed Zika symptoms while they were pregnant.
The study was conducted by Colombian and American health officials, tracking reports of Zika infections and of birth defects seen between early last August and early April.
It was published online in the New England Journal of Medicine.
The Zika virus is spread mainly through the bite of a tropical mosquito, the Aedes Aegypti (pictured) – but can also be spread sexually as the virus can live for months in semen