The 2016 Rio de Janeiro Olympics are shaping up to be some of the most competitive Games yet. However, they could be missing some of the world’s top athletes, all because of the threat of the Zika virus. The presence of the virus in South America, and particularly in Brazil, has prompted many top athletes, especially female athletes, to question whether or not they want to participate.

Numerous high level athletes have threatened to miss the games due to Zika. Hope Solo, star goalkeeper for the United States Women’s soccer team, has said that if she had to decide right now, she would skip the games due to the potential risk to her future children. Great Britain Track runner Jessica Ennis-Hill, who won the Gold in the Heptathlon last games, says that she is monitoring the outbreak closely before she decides whether or not to participate. Kenya was considering not sending any teams because of Zika, but has since decided that they will participate in the Rio Games.

Athletes have also spoken out saying that Zika is not deterring their plans for Rio. US Sprinter DeeDee Trotter said in an interview she wasn’t worried, “if the only danger is to women who are pregnant.” Male athletes like US Tennis player John Isner said that he is taking precautions before going, but is not worried about contracting the virus or about any long-term effects.

The biggest consideration for female athletes is the potential to not know about a pregnancy and competing in the games anyway,.like Kerry Walsh-Jennings, who didn’t know she was pregnant while she was competing in London. There has also recently been a fear that Zika could be transmitted through sex or saliva, which would put both male and female athletes at risk for contracting the virus, regardless of the potential for birth defects.

Zika was first identified in Uganda in 1947, and progressed through states in Africa, Asia and Oceania. In 2015, there was a Zika outbreak in South America as well as an increase in the birth defect Microcephaly. Microcephaly causes incomplete brain development and thus, a small and deformed skull, which often leads to a short life. While there was no proven causal link between the two, it was widely accepted that Zika was the reason for these abnormalities. Since the 2015 outbreak, the World Health Organization as well as the CDC and its equivalent institutions around the world have come out with recommendations to avoid Zika.

As more research has been done about Zika and its potential long-term consequences, it has become increasingly clear that the fears of athletes are largely unfounded. As far as any study can conclude up to this point, only women who are pregnant at the time of their contraction of Zika are at any sort of measurable risk for their children having birth defects. Considering there have only been 18 women in the modern Olympics who have competed while pregnant, this is not a huge deterrent for female athletes. There is also a less substantiated fear that the virus can lay dormant in the body and affect pregnancies in the future, even if the mother is not experiencing symptoms anymore. While this hasn’t been proven, the WHO and the CDC recommend that women either postpone traveling to areas where Zika is most prevalent, or wait 6-8 months after traveling to try and become pregnant. While this fear could still make female athletes hesitant to participate in the Games, any link that there is between Zika and birth defects like Microcephaly is easily circumvented by heeding these warnings.

Overall, education about avoiding Zika and its possible causal relationship to birth defects is the best way to avoid a boycott of the Rio Olympics. If athletes are aware of the best ways to avoid getting sick, and are aware of the post-Olympics guidelines for limiting their chances of passing on the infection to their unborn child, fewer athletes will remain hesitant about competing in the games.