The rapid spread of the Zika virus in Latin America is causing concern around the world.Spread by mosquitoes, the virus is being linked to birth defects in babies born to women who have been infected.With cases now also having been reported in Australia, Thailand and the US, among others, the World Health Organization has declared the virus a global public health emergency.So, how should we interpret the WHO's warning?How concerning is this outbreak?And what are the affected countries doing to combat the spread of the virus?