"If a person is infected and then travels to a country where the Aedes mosquito is present, the mosquito can bite the person and thereby introduce the virus in a place where it previously did not exist," Bellei said.

International Olympic Committee president Thomas Bach said on Jan 28 that the committee will make its best effort to keep the Rio Olympics safe from the Zika virus.

"We will do everything to ensure the health of the athletes and all the visitors," Bach said during a visit to Athens, Greece, adding that a circular on the issue would go out to national Olympic committees by Jan 29.

"The Olympic Games will take place during the Brazilian winter, so we will also have different climatic conditions," he also emphasized.

"We are in close contact with the World Health Organization, as well as with the organizing committee and Brazilian authorities," he added.

The Zika virus is believed to have originated in Africa and is thought to have been spread to Brazil by tourists in 2014.

Local health officials say the mosquito is behind a rise in the incidence of microcephaly, a condition that causes unusually small infant head size. It can lead to stillbirths and long-lasting health problems for survivors.

Brazil's Ministry of Health has recorded 4,180 suspected cases of Zika-related microcephaly since October. Less than 150 cases were reported in the country in 2014.

The Washington Post reported on Jan 29 that after experts examined 732 of the cases they found that more than half of them were not microcephaly or were not Zika virus related.

The Pan American Health Organization (PAHO) issued an epidemiological alert against the Zika virus in May, but given the relatively mild effects of the mosquito bite, it wasn't until growing evidence suggested a link to birth anomalies that governments sprung into action.

The virus is "now circulating in 18 countries and territories in Latin America and the Caribbean", PAHO said in its latest update on Jan 18, recommending that countries "strengthen prenatal care" and continue efforts to eradicate mosquitoes.

The health alert coincides with Brazil's worst recession in decades, exacerbated by a sprawling corruption scandal at state-run oil company Petrobras.

Rio is also struggling to finish a raft of infrastructure projects in time for the Olympics, including a new subway line and several event venues.

In addition, Olympic organizers have cut about $500 million from their budget while Rio's sailing and rowing venues face ongoing pollution concerns linked to the city's sub-standard sewage system.