GENEVA • The World Health Organisation (WHO) said yesterday that it will know in a matter of weeks whether the Zika virus causes microcephaly and neurological illness Guillain-Barre syndrome.

The UN health agency also said large-scale trials for vaccines against the virus are at least 18 months away.

WHO's deputy director for health systems and innovation, Ms Marie-Paule Kieny, told journalists it will take an estimated four to eight weeks to establish whether Zika causes microcephaly - a condition that can cause babies to be born with abnormally small heads and brains - and Guillain-Barre syndrome, which can cause paralysis or even death.

"We have a few more weeks to be sure to demonstrate causality, but the link between Zika and Guillain-Barre is highly probable," said Ms Kieny.

While most people infected with Zika have only mild symptoms, rising global anxiety about the virus is driven by its strongly suspected link to the two more serious conditions.

An estimated 15 companies or groups have begun work on a vaccine for the virus, the spread of which has been declared an international health emergency.

There are currently two vaccine candidates which appear most promising - one being developed by the United States' National Institutes of Health and another from India-based Bharat Biotech, said Ms Kieny.

Zika has spread rapidly through Latin America and the Caribbean, with Brazil the worst-hit, followed by Colombia.

But cases have been reported around the world.

Venezuelan President Nicolas Maduro said on Thursday that three people had died of complications linked to the mosquito-borne Zika virus and that the number of suspected cases of Zika had risen to 5,221.

Brazil also said on Thursday that three people who died last year had the Zika virus, although the authorities could not confirm that Zika alone was responsible for their deaths.

Meanwhile, a second pregnant woman had been diagnosed with the Zika virus in Australia, officials said yesterday, adding that the disease was acquired overseas and there was no public health risk.

The confirmation comes after a pregnant woman in the northern state of Queensland was diagnosed with the virus on Tuesday.

In south-west China, the border province of Yunnan is on high alert for Zika, providing 24-hour laboratory tests for the virus after China confirmed its first imported case of the virus on Tuesday.

Yunnan shares borders with Myanmar, Laos and Vietnam, and China's National Institute for Viral Disease Control and Prevention has warned that the virus is spreading not only in Latin America but also in some South-east Asian countries that are popular destinations for Chinese tourists.

AGENCE FRANCE-PRESSE, REUTERS, XINHUA