Concerns about the spread of the Zika virus in the Americas have prompted the World Health Organisation (WHO) to convene an expert panel to determine if the outbreak constitutes a global health emergency, WHO chief Margaret Chan said today in Geneva.

"The level of alarm is extremely high," Chan told WHO member state representatives meeting in Geneva, adding that the virus was spreading "explosively" in the region. The panel is set to meet Monday.

In most patients, the Zika virus causes only mild symptoms including fever and rashes. However, there are concerns that, in cases where a pregnant women is infected, the child might eventually be born with a head malformation.

There are also indications that the Zika virus might be linked to cases of Guillain-Barre muscle weakness syndrome.

Chan emphasized that more research was needed to establish what connections, if any, there are between Zika and the other health problems.

There are estimates that there may have been 1.5 million Zika cases in Brazil, where the outbreak started last year, a senior WHO official said. A senior Brazilian health official said via video link that some 4,000 babies had been born with unusually small heads amid the outbreak.

Besides the observed birth defects and neurological syndromes, Chan said WHO was also deeply concerned because of the risk that the virus might spread further through mosquitoes, because people in the Americas lack immunity, and because there is currently no vaccine or rapid diagnostic method.

"Moreover, conditions associated with this year's El Nino weather pattern are expected to increase mosquito populations greatly in many areas," Chan said, referring to the warming of ocean temperatures that occurs every few years.

The disease, which is spread by mosquitoes, has spread to 24 countries and territories in the Americas including the United States.

A man tested positive for the virus in a Danish hospital this week, but local health authorities said there was no risk of an epidemic since the Aedes mosquito is not found in the country.

WHO has recommended pregnant women avoid mosquito bites and consult doctors before planning a trip to countries where the virus is circulating.

Marcos Espinal, a senior expert in WHO's Americas branch, said the main tasks now were to strengthen health systems in affected countries, step up mosquito control and speed up research on the disease.

"We don't even know yet if this virus crosses the placenta from mother to child,” he said.

- dpa