The risk of Zika virus infections at the Olympic Games in Rio de Janeiro is low and has been overcome, health officials in Brazil said on Sunday, five days before South America's first Games are due to begin.

Rio de Janeiro's health secretary, Daniel Soranz, said Zika should not deter travelers from coming to the Games, as cases of the virus had dipped significantly in recent months.

The mosquito-borne virus has been linked to microcephaly, a birth defect among babies of pregnant mothers infected by Zika, and its discovery in Brazil last year led to concern over the Games, which are expected to attract some 500,000 visitors.

However, with dry and cooler weather in Rio amid the southern hemisphere winter, the incidence of Zika and other mosquito-borne diseases such as dengue and Chikungunya has declined sharply in recent months.

"Since November of last year, we have already been showing projections and scientific studies that show this won't be an issue during the Olympics," Soranz told a news conference.

"Since two weeks before the Games, the number of cases were almost non-existent. In the city, cases are very rare and for us it is an issue that we have more than overcome," he said.

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Some 500,000 people are expected to visit the Rio Olympics, which have been overshadowed not only by Zika but also by concerns over crime and delays to infrastructure.

The metro line due to carry visitors from the city center to the distant western neighborhood of Barra de Tijuca that is hosting the Games was inaugurated only on Saturday.

Despite the alarm over Zika, U.S. government epidemiologists estimated in June that the Olympics presented only tiny risks of propagating the epidemic, which has spread rapidly through the Americas since it was discovered in Brazil last year. They noted that an estimated 240 million people travel yearly to areas infected with the virus, and said 500,000 more in Rio was not a major threat.

Zika is spread primarily through the bite of an infected mosquito, although it can also spread through sexual transmission.