Stopping Zika's spread in Puerto Rico

Zika has hit 31 countries is South America so far, and is thought to be fast approaching mainland US. So far there have only infections by travel or sexual contact in that part of the world.

The virus is spread by the aedes aegypypti mosquito which is found in some southern states of the US. The BBC has been given special access to the Centers for Disease Control's labs on the Caribbean island of Puerto Rico.