Zika virus 'spreading explosively', millions of cases expected, World Health Organisation says

The World Health Organisation expects the Zika virus, which is spreading through the Americas, to affect between 3 million and 4 million people, a disease expert says.

 The WHO's director-general said the spread of the mosquito-borne disease had gone from a mild threat to one of alarming proportions.

Marcos Espinal, an infectious disease expert at the WHO's Americas regional office, said: "We can expect 3 to 4 million cases of Zika virus disease", but he gave no time frame.

There is no vaccine or treatment for Zika, which is a close cousin of dengue and chikungunya and causes mild fever, rash and red eyes.

An estimated 80 per cent of people infected have no symptoms, making it difficult to know whether they have been infected.

WHO director-general Margaret Chan said the organisation would convene an emergency committee on Monday to help determine the level of the international response to an outbreak of the virus spreading from Brazil that is believed to be linked to severe birth defects.

"The level of alarm is extremely high," Ms Chan told WHO executive board members at a meeting in Geneva.

Zika is now spreading explosively.

"As of today, cases have been reported in 23 countries and territories in the [Americas] region."

Five French citizens who were infected with the Zika virus while travelling abroad have returned home since the beginning of the year, authorities there said.

"None of the patients presented a severe form of the infection," the Health Ministry said in a statement, without naming the regions where the five had been travelling.

"There is no actual risk of transmission of the Zika virus in mainland [France]," the ministry added.

Three Canadians had also been infected with the virus while travelling abroad, Canadian health authorities said.

"We have no reason to believe that local transmission is a concern for Canadians," Canadian Health Minister Jane Philpott said, while urging travellers to take precautions.

 A man wearing protective clothing sprays grave stones with a fumigation machine

PHOTO: A specialist fumigates the Nueva Esperanza graveyard in the outskirts of Lima. (AFP: Ernesto Benavides)

Virus may also be transmitted through sex