US researchers are estimating a wide range of potential risk for the birth defect microcephaly following Zika infection in the mother, putting the figure at anywhere between 1 per cent and 13 per cent, according to new findings.
Their findings are based on statistics from a 2013 Zika outbreak in French Polynesia and ongoing reports of the virus and birth defects in Brazil's Bahia state during the current outbreak.
The analysis was conducted by the US Centers for Disease Control and Prevention (CDC) and published in the New England Journal of Medicine.
Microcephaly is a rare birth defect marked by unusually small heads and can cause developmental problems. Brazil’s ministry of health has confirmed 1,434 cases of microcephaly that it believes are related to Zika infection throughout the country, according to data released this week.
The CDC researchers said the highest potential risk for microcephaly appears to be when the mother is infected during the first three months of pregnancy, after which the risk was greatly reduced.
Zika is carried by mosquitoes, which transmit the virus to humans. It can also be transmitted through unprotected sex with an infected man.
The analysis found the risk of having a baby with microcephaly in the French Polynesia outbreak was 1 per cent. But in Brazil, where the outbreak is far more widespread, that is likely to be higher and the alarming numbers of cases of severe microcephaly have surprised experts.
CDC researchers, however, noted several limitations of the report. It said the available data are very limited, especially in recently affected areas such as Bahia, where total infection rates are unknown and microcephaly cases are still being reported.
In addition, most people infected with Zika show no symptoms, meaning little is known about the effects of mild infections early in pregnancy, when women may be unaware they are pregnant.
They also cautioned that microcephaly may be just one of a range of potential problems with foetal development that are linked to Zika.– (Reuters)