WHO predicts up to four million Zika cases this year

The World Health Organisation has warned that between three to four million could be infected with the Zika virus in the Americas this year. Although most people will not develop symptoms, the infection has been linked to brain defects in babies.

"Zika has gone from a mild threat to one of alarming proportions,” WHO director general Margaret Chan said, adding that she has set up a Zika "emergency team" that will decide on Monday whether the pandemic should be treated as a global emergency.

The last time the WHO declared a global emergency was for the Ebola outbreak in West Africa that killed over 11,000 people.

Zika, which is spread by mosquitoes, was first detected in Uganda in 1947, but has never caused an outbreak on this scale.

Brazil reported the first cases of Zika in South America in May 2015, and WHO officials estimate that between 500,000 and 1.5 million people have been infected in the country since then.

It has now spread to over 20 countries in the region. At the same time there has been a steep rise in levels of microcephaly - babies born with abnormally small heads - and the rare nervous system disorder Guillain-Barre syndrome.

Although the link between the virus and these disorders has not been confirmed, Chan admitted that it was "strongly suspected" and was "deeply alarming".

Moreover, she warned that the situation could yet deteriorate as "this year's El Nino weather patterns are expected to increase mosquito populations greatly in many areas".

Earlier, doctors writing in the Journal of the American Medical said that Zika had "explosive pandemic potential" and said that the WHO's failure to act swiftly on Ebola probably cost thousands of lives.

“The level of concern is high, as is the level of uncertainty,” Chan told an executive board meeting of the WHO. "Questions abound - we need to get some answers quickly.

"For all these reasons, I have decided to convene an Emergency Committee.

"I am asking the Committee for advice on the appropriate level of international concern and for recommended measures that should be undertaken in affected countries and elsewhere."

Officials from the US National Institute of Health said they had two potential Zika vaccines in development.

One that is based on an experimental West Nile vaccine could be repurposed for Zika and enter clinical trials by the end of 2016, Dr Anthony Fauci from NIH said.

He said talks were already taking place with pharmaceutical companies, but a vaccine would not be widely available for several years.

Meanwhile Anne Schuchat, from the Centers for Disease Control confirmed there had been 31 cases of Zika in the country - all linked to travel to the affected areas.

Carissa Etienne, the regional-director for the WHO Pan American Health Organization, said the link between the abnormalities and Zika had not been confirmed.

But she added: "We cannot tolerate the prospect of more babies being born with neurological and other malformations and more people facing the threat of paralysis."