An open letter to the U.N. health agency, signed by almost 150 public health experts, calls for the games to be delayed or relocated "in the name of public health."
It cites recent scientific evidence that the Zika virus causes severe birth defects, most notably babies born with abnormally small heads. In adults, it can cause a rare and sometimes fatal neurological syndrome.
Several public health academics have previously warned that hundreds of thousands of people heading to the August 5-21 games in Brazil will lead to brain-damaged babies and speed up the virus' global spread.
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Zika virus: pregnant women shouldn't travel to Brazil