The Zika virus has been linked with microcephaly. This is a birth defect that means the baby is born with an abnormally small head and underdeveloped brain. In the worst cases, this can be fatal as the brain is so underdeveloped that it cannot manage even the most basic functions needed for life. In less severe cases, children may survive but will probably face developmental and learning difficulties. Nobody's quite sure how the Zika virus causes microcephaly, or even if it does. At the moment, the link between the two is circumstantial and unconfirmed, but the key to understanding it may lie in some other infections with similar effects. Cytomegalovirus, or CMV, can also cause microcephaly and brain abnormalities. Again, it's not thoroughly understood, but some studies suggest that the virus attacks the stem cells during early development. Brazil has seen a breathtaking explosion in cases of microcephaly in a relatively short period of time. In the whole of 2014, there were just 150 cases of the defect. Since October of 2015, we have seen more than 4,000 cases and that number is ever increasing. The threat is so great in countries such as Brazil that women are being advised to completely avoid getting pregnant in the next couple of years. So where did it come from?
