Paris: A woman infected by the Zika virus during the first three months of pregnancy faces a one-in-100 chance her child will suffer severe brain damage, according to a study released today.
Zika increases the risk of microcephaly — an otherwise rare condition that results in an abnormally small head — by fifty-fold, the researchers calculated.
“The first trimester is the most critical,” lead author Simon Cauchemez, a scientist at the Institut Pasteur in Paris, told AFP.
His team’s statistical analysis of a Zika outbreak in French Polynesia in 2013-14 that spread to two-thirds of the population is the most rigorous attempt yet to quantify the risk of microcephaly, which emerges in foetuses.
Brazil has been hardest hit by the mosquito-borne virus, with some 1.5 million people infected and 745 confirmed cases of the brain-deforming syndrome, but the ongoing epidemic and patchy data have thwarted similarly rigorous analyses.
One study from Brazil estimated the chance of birth defects for mothers carrying the virus during pregnancy at more than 20 percent, but carried a very large margin of error.
All told, some 40 countries have reported transmission within their borders since last year, according to the World Health Organization, which declared a global health emergency on February 1.
The new research does not prove that Zika causes the brain-deforming syndrome.
But recent experiments, including one showing that the virus singles out and attacks cells crucial to brain development, have left little doubt in the minds of many researchers that Zika is to blame.
A flurry of studies has also established strong links to other rare neurological disorders, including one — Guillain-Barre syndrome — in which immune defences turns against the body’s nervous system, sometimes causing lasting damage or even death.
A number of factors in French Polynesia — its small population, universal medical records, an epidemic with a clear beginning and end — created laboratory-like conditions favourable to research.