JAKARTA - An Indonesian research institute said Sunday it had found one positive Zika case on Sumatra island, adding that the virus has been circulating in the country "for a while".

Indonesia's health ministry could not immediately comment on the report by the Eijkman Institute for Molecular Biology.

The mosquito-borne virus has sparked widespread alarm in parts of the Americas. It is suspected of causing grave brain damage in newborns and has similar symptoms to dengue fever.

The institute said a 27-year-old man living in Jambi province on Sumatra island who had never travelled overseas had been found to be infected.

It said it stumbled on the case while studying a dengue outbreak in the province.

Researchers set aside specimens which produced dengue symptoms such as rashes and fever but which tested negative for dengue, and researched them further.

"Out of the 103 (dengue-negative) specimens that we checked, we found one positive for Zika," the institute's deputy director, Herawati Sudoyo, told AFP.

Zika is transmitted by the Aedes aegypti mosquito, which also spreads dengue fever and the chikungunya virus. It produces flu-like symptoms including a low-grade fever, headaches, joint pain and rashes.

Sudoyo said the specimens were taken during a dengue outbreak in Jambi between December 2014 and April 2015. It was not known how and when the man, who never travelled overseas, contracted the virus.

"We concluded that the virus has been circulating in Indonesia for a while," Sudoyo said.

The World Health Organisation warned in the past week the virus is "spreading explosively" in the Americas, with three million to four million cases expected this year. Hardest-hit so far has been Brazil, with more than 1.5 million cases since April.

Health authorities there are investigating the possible linkage between Zika and more than 3,400 suspected cases of microcephaly - abnormally small skulls and brains - in babies born to infected mothers.

OVER 2,100 COLOMBIAN

WOMEN INFECTED WITH ZIKA

More than 2,100 pregnant Colombian women are infected with the mosquito-borne Zika virus, the country's national health institute said.

There are 20,297 confirmed cases of the disease in Colombia, the national health institute said in a epidemiology bulletin, among them 2,116 pregnant women.

There are so far no reported cases of microcephaly or deaths from the virus in Colombia.

The institute said 37.2 percent of pregnant women with Zika live in Norte de Santander province, along the eastern border with Venezuela. Earlier figures from the health ministry showed 560 pregnant women had the disease, out of more than 13,500 infections.

Zika cases have been confirmed in 23 countries and territories in the Americas and scientists are racing to develop a vaccine for the virus.

Nearly half of Colombia's Zika cases have been reported in the country's Caribbean region, the bulletin said. More than 60 percent of those infected are women.

The health ministry has said Zika infection falls within the health requirements women must meet to get abortions in the country, which restricts the procedure unless patients are victims of rape, have significant medical problems or the fetus is fatally deformed.

Many women, especially those living far from large cities, struggle to find abortion providers even when they meet the legal requirements and illegal abortions are widespread.

The government has urged women to delay pregnancy for six to eight months to avoid potential infection. Officials expect up to 700,000 cases.

Brazil is the country hit hardest by the disease. It has reported around 3,700 cases of microcephaly strongly suspected to be related to Zika.

The World Health Organization has said as many as 4 million people in the Americas may become infected.