In an open letter sent to the World Health Organization (WHO) on Friday, the experts said the games should be delayed or relocated "in the name of public health."

"The Brazilian strain of Zika virus harms health in ways that science has not observed before," the letter said. "An unnecessary risk is posed when 500,000 foreign tourists from all countries attend the games, potentially acquire that strain, and return home to places where it can become endemic."

The letter was signed by 150 experts, including bioethicists, scientists and doctors, and was addressed to WHO Director General Margaret Chan.

Zika has been linked to microcephaly, a birth defect marked by an abnormally small head in babies that can lead to severe developmental problems. Around 1,300 babies have been born with microcephaly in Brazil since the virus started circulating there early last year. Zika has also been connected with Guillain-Barre, a paralyzing and potentially fatal neurological syndrome that causes the immune system to attack nerves.

Zika cases going up

The WHO in February declared a public health emergency over Zika, which spreads via mosquitoes and sexual contact.

The signatories of Friday's letter, who come from over a dozen countries, pointed out that despite increased efforts to wipe out Zika-bearing mosquitoes, infections in Rio had continued to rise.

"The fire is already burning, but that is not a rationale not to do anything about the Olympics," said Amir Attaran, a professor at the University of Ottawa and one of the letter's authors. "It is not the time now to throw more gasoline onto the fire."

The WHO has already advised pregnant women not to attend the games, while other travelers have been told to exercise caution and avoid overcrowded areas.

Conflict of interest?

Friday's letter also called on the WHO to convene an independent group to advise it and the International Olympic Committee (IOC) on the Zika situation. It questioned whether the UN health agency was able to make an unbiased assessment given its close collaboration with the IOC.

"WHO cannot credibly assess the public health risks of Zika and the Olympics when it sets neutrality aside," the letter stated.

The WHO has not yet responded to the letter. In an email to the Associated Press, the IOC said it would "always consult the WHO for guidance and advice on health matters."

nm/gsw (Reuters, AP)