The Zika virus is “spreading explosively”, the head of the World Health Organisation has warned amid fears it may be carried by the common mosquito.
Speaking at a meeting of WHO member states, Director-General Dr Margaret Chan said the level of alarm over the virus has become “extremely high”.
The mosquito-borne virus has been linked to a steep increase in the number of babies born with severe birth defects, including abnormally small heads.
“A causal relationship between Zika virus infection and birth malformations and neurological syndromes has not yet been established, but is strongly suspected,” the WHO chief said.
“The possible links, only recently suspected, have rapidly changed the risk profile of Zika, from a mild threat to one of alarming proportions,” she added.
Dr Chan has called an emergency meeting on 1 February to discuss whether the outbreak, which is taking hold across South and Central America and the Caribbean, qualifies as an international public health emergency.
The WHO warning came as scientists in Brazil said it is possible the virus is carried by the common mosquito.
Up until now it was thought the Aedes aegypti mosquito, which is confined to the tropics, was solely spreading the virus.
Cases have so far been reported in 23 countries and territories, with Brazil among the worst affected.
Between three and four million cases of the virus are expected, infectious disease expert Marcos Espinal warned, although he did not give a time frame.
US health authorities have confirmed 31 reported cases of the Zika virus in the country among people who have travelled to affected areas.
A small number of Europeans have also tested positive, including five British travellers.
The Foreign Office is advising pregnant women to reconsider travel to affected areas while France’s health minister has gone a step further and “strongly” urged pregnant women to postpone their trips.
In several of the affected areas, including El Salvador and Colombia, women have been advised not to get pregnant altogether.
There are no known vaccines, specific treatments or rapid diagnostic tests for the virus, something the WHO has highlighted as a particular concern.
With the exception of the risks for unborn babies, Zika is not considered dangerous.
Common symptoms can last up to a week and include fever, rashes, joint pain and conjunctivitis.