The World Health Organisation has designated the Zika virus a public health emergency of international concern, an action it has taken only three times before, which paves the way for the mobilisation of more funding and manpower to fight the mosquito-born pathogen spreading "explosively" through the Americas.
Zika, which was first identified more than 50 years ago, has alarmed public health officials in recent months as it was potentially linked to thousands of cases of brain defects in newborns. Estimates are that the virus will infect up to 4 million people in the coming year.
The declaration represents the WHO's highest level of alert and is only invoked in response to the most dire threats. The first time was in 2009 during the H1N1 influenza epidemic that is believed to have infected up to 200 million worldwide; the second in May 2014 when a paralysing form of polio re-emerged in Pakistan and Syria; and the third in August 2014 with Ebola in West Africa.
Infectious disease experts and others have been pressuring the WHO to escalate its response to Zika for several months, warning of the mistakes world leaders made during the Ebola crisis when a lack of coordination delayed quarantines and treatment.