It could take years to learn how long men infected with Zika are capable of sexually transmitting the virus, which can cause crippling birth defects and other serious neurological disorders.

In the meantime, health officials have warned couples to refrain from unprotected sex for six months after a male partner is infected. The extraordinary recommendation, based on a single report of Zika surviving 62 days in semen, could affect millions.

The grave risks associated with Zika, along with its potential reach, are driving U.S. health authorities to pursue research even though funding is mired in Congressional gridlock. A study of sexual transmission risk is one example of science that health officials said can't wait for politics.