An urgent global race is under way to establish how and why the Zika virus could be causing a devastating spike in cases of babies being born with underdeveloped brains in South America.
Brazil has reported around 4,000 cases of microcephaly since October – an unprecedented number.
The World Health Organization has declared a global public health emergency in response.
But experts are unsure what exactly is behind the rise.
Zika virus has now hit more than 20 countries and the WHO believes it is likely to spread “explosively” across nearly all of the Americas, making the need for fast answers clear.