GENEVA, Switzerland (AFP) — The Zika virus is “spreading explosively” in the Americas, and the region may see up to four million cases of the disease strongly suspected of causing birth defects, the World Health Organization (WHO) said yesterday.

As the number of suspected cases of microcephaly — thought to be linked to the virus — surged in Brazil, WHO head Margaret Chan said an emergency committee would meet on February 1 to determine whether the outbreak amounts to a global health emergency and how the world should respond.

The number of microcephaly cases in Brazil has soared from 163 a year on average to more than 3,718 suspected cases since the outbreak, and 68 babies have died, according to the health ministry.

The condition causes babies to be born with an abnormally small head and a neurological disorder called Guillain-Barre syndrome.

Colombia, Ecuador, El Salvador and Jamaica have warned women to avoid getting pregnant for the time being, while France has urged women not to travel to French overseas territories in South America and the Caribbean.

Chan told an assembly of WHO member states in Geneva that the severity of the current outbreak was unprecedented in recent decades.

For decades after the Zika virus was first discovered in Uganda in 1947, the mosquito-borne virus was of little concern, sporadically causing “mild” illness in human populations.

“The situation today is dramatically different. The level of alarm is extremely high,” she said.

“A causal relationship between Zika virus infection and birth malformations and neurological syndromes has not yet been established, but is strongly suspected,” Chan said.

She told WHO members that the virus “is now spreading explosively” in the Americas, where 23 countries and territories have reported cases.

Marcos Espinal, the head of communicable diseases and health analysis at the WHO’s Americas office, said the region could see between three to four million cases of Zika infections.

That projection applied to the next 12 months and was based largely on historical spread patterns of similar mosquito-borne diseases like dengue fever, said Sylvain Aldighieri a WHO epidemic expert in the Americas.

Espinal drew a contrast with Ebola, which is transmitted through the bodily fluids of infected people and those who have died from the disease.

Zika virus “will go everywhere the mosquito is”. Espinal said. “We should assume that. We should not wait for it to spread,” he added, stressing that controlling the carrier mosquito was crucial to controlling the outbreak.

WHO has previously said that it expects the Zika virus to spread to every country in the Americas except Canada and Chile.

There have not yet been any cases of local transmission of Zika virus within the United States, although infected travellers have returned to the country after visiting other areas.

However, a recent study in

The Lancet suggests that Zika virus could reach regions of the United States in which 60 per cent of the population lives, or some 200 million Americans.

Chan explained that the February 1 emergency meeting would assess the severity of the outbreak and what response measures might be taken.

It will also aim to identify priority areas for urgent research, Chan said, after US President Barack Obama called for swift action, including better diagnostic tests as well as the development of vaccines and treatments.