In Brazil, there have been around 1,500 cases of microcephaly—where babies are born with a small head, and the brain is underdeveloped—since early 2015. The Zika virus, carried by mosquitoes, has been blamed, but researchers from the New England Complex Systems Institute doubt this.
The researchers have investigated the cases of more than 12,000 women in Colombia who have all been infected by the virus—and yet none have given birth to a baby with microcephaly.
Yet, the mothers of the four cases that were reported in the country hadn’t been infected. The rate of cases in Colombia is in line with general population expectations of two cases per 10,000 births.
Instead, scientists need to look for other causes. Several have been mooted: some suspect that the pesticide, pyriproxyfen, added to the public water supply in some regions of Brazil, could be to blame, while others point to a vaccination programme for pregnant women that began nine months before the first babies with microcephaly were born.