The World Health Organisation (WHO) has warned that the Zika virus could become a global pandemic. Scientists say the outbreak could be more serious than the Ebola virus. Ebola killed over 11,000 people. The WHO estimated that the Zika virus could affect four million people this year. The virus is advancing across South and Central America. Dr Margaret Chan of the WHO warned that Zika is "spreading explosively". She added that it has quickly gone from being a mild to a serious threat. The mosquito that carries the virus is spreading worldwide because of warmer weather.

The Zika virus is linked to a rise in birth defects in South America. Scientists say it causes a disease called microcephaly. This is where a baby is born with a smaller head, and with brain damage. In Brazil there were around 4,000 babies born with microcephaly last year. In 2014, there were just 150 cases. Colombia's government just reported that more than 2,100 pregnant women in Colombia have the virus. It is difficult to find a vaccine for the Zika virus. A doctor said a vaccine needs to be tested on pregnant women. This would be "a practical and ethical nightmare".