The Zika virus was discovered in a Ugandan forest in 1947.

It was first identified in rhesus macaque monkeys when scientists were conducting routine surveillance for yellow fever there.

But the virus, which has since made headlines around the world, soon spread beyond Africa to Asia. The first large outbreak later occurred on the Pacific island of Yap in 2007. But it was only last year, when Zika surfaced in Brazil, that people started to take notice.

According to the World Health Organisation (WHO), 70 countries and territories have now reported evidence of mosquito-borne Zika virus transmission since 2007, with 67 of them reporting it since last year .

Twenty countries or territories, including Costa Rica and Haiti, have reported microcephaly and other central nervous system malformations potentially associated with Zika virus infection or congenital infection.

From reports received by the WHO from the national health authorities, there have so far been no laboratory-confirmed cases of Zika virus in spectators, athletes or anyone associated with the Olympic Games held in the Brazilian city of Rio de Janeiro this year. The situation is still being closely monitored, the WHO said.

The Zika virus is spread by the Aedes aegypti mosquito, which is also a vector for dengue and chikungunya.

Symptoms, if any, are generally mild and include fever, conjunctivitis and rashes, which go away within a week.

Of greater concern is Zika's association with microcephaly - a condition where a baby is born with a small head. Babies with microcephaly often have smaller brains that may not have developed properly.

Last week, Singapore announced its first locally transmitted case when a 47-year-old woman tested positive for Zika. The news came after a 48-year-old Singapore permanent resident who had returned from Brazil tested positive for Zika in May.

As of Wednesday, the total number of local transmissions stands at 115.

Carolyn Khew