 The Zika virus has been around in humans since 1952, when the first case was documented in Africa, a continent with close to double the land mass of South America. Why only now has it become an epidemic? What's changed? The virus may have changed, but there's no doubt that we have. We now travel more, live closer together and our planet's climate has become warmer and wetter. Born in shallow pools of water, the Aedes aegypti mosquito is a carrier of the Zika virus and others such as yellow fever and dengue. Unlike us, it only travels an average of 400 metres from where it's born. A female mosquito's top priority is to lay eggs and to do so she must feed, and so she goes hunting, biting in an attempt to find a rich source of nutrition, blood. If she's carrying the Zika virus, it can enter the fresh wound, leaving a small amount of the virus behind. The virus can now multiply, often unnoticed, triggering a relatively minor fever and rash in around a fifth of those infected. And when an uninfected mosquito bites an infected person, the virus can be passed along again, continuing the cycle. Largely oblivious to the infection, we carry on, living, working and travelling. As a consequence, Zika has hopped the globe from Africa through several countries and smaller islands until it reached South America. Here, the huge landmass and dense populations now exposed to Aedes aegypti means that infection can spread. And because most of us have never been exposed to the virus, our immune systems are unable to fight back. For Zika and Aedes aegypti, geographical borders are irrelevant. They'll continue to spread as long as population density, urban living and environmental change allow. Unless we do something. So what do we do? Well, if local communities and global organisations work together, we can share ideas that will help us slow the rate of Zika's spread. We can monitor the movement of other diseases and create new drugs and vaccines and develop other public health measures to make sure that the next time we encounter a new infection, we're better prepared.