Four people suffering from the Zika virus in Florida are probably the first cases contracted within the US, health officials say. So far, cases outside of Latin America and the Caribbean, where the virus is prevalent, have been spread by travel to that region or sexual transmission. The four Florida cases mean US mosquitoes may be carrying the virus. Zika causes only a mild illness in most people but the virus has been linked to severe brain defects in newborns.

Zika virus: Florida cases 'likely' to be first US-based infections