How realistic is the potential global spread of Zika virus and should we all be worried?

Unless you have taken a holiday on Mars for the whole of this year no doubt by now you will have heard of Zika. This is the virus that has emerged in the last 18 months to cause an epidemic in South and Central America. Currently, at least 50 countries are known to have active Zika transmission. Most infections occur with either very mild flu-like symptoms or, far more often, are in fact symptomless, i.e. the person is not ill. However, it is a strikingly different story for newborn babies, who can suffer from a condition called microcephaly, literally having a small head – and hence an underdeveloped brain. In Brazil, the centre of the current outbreak, more than 5,000 cases of babies born with brain defects have been reported. These appear to be associated with Zika infection of the pregnant mother, from whom it is passed to the foetus in her womb. Scientists are still determining the direct role played by the virus and if it responsible in all instances.