​New Zealander middle-distance runner Nick Willis and his wife already have a toddler, and they're looking to add to their family. Concern over the Zika virus is putting those plans on hold.

Willis, the 2008 Olympic silver medallist in the 1,500 metres, hopes to compete this summer at the games in Rio de Janeiro. Wife Sierra is one of his coaches.

"We've had a lot of conversations about the Zika virus. ... We have a 2 1/2-year-old son, my wife and I, and we'd like to add to that family and grow it," Willis said. "The biggest impact, I suppose, is we've decided not to try to get pregnant now."

Willis, 32, suggested that perhaps he'd consider freezing his sperm until the couple knows more about the virus. Like many athletes headed to Brazil this summer, he is refusing to let Zika derail his Olympic dreams. Most say they are trusting federations to make sure they are safe, although one medal hopeful is warning a vulnerable relative to stay home.

The husband of American Jenn Suhr, who holds the world indoor record for the pole vault and won the gold at the 2012 Olympics, said a cousin cancelled plans to go to Brazil this summer to watch Suhr jump because the cousin has one child and is expecting another.

"We've never been to South America. We don't know what we're in for down there," Rick Suhr said. "As long as they keep putting these events in challenging cities, you're going to have challenging issues come up. It seems like the farther you compete from home, the more challenging it is."

The Zika virus — spread mainly by mosquito bites — is epidemic in Latin America and the Caribbean. The virus causes mild illness or no symptoms in most people. But in Brazil, officials are investigating a possible link to babies born with unusually small heads, a rare birth defect called microcephaly that can signal underlying brain damage.

In guidance issued Friday night, the U.S. Centers for Disease Control and Prevention addressed people planning to travel to Brazil for the Olympics in August and the Paralympic Games in September. The agency again advised that pregnant women consider not going and that their male sexual partners use condoms after the trip or abstain from sex during the pregnancy.

Women who are trying to become pregnant should talk to their doctors before making the trip, the CDC advised.

The CDC also recommends that all travellers use insect repellent while in Zika outbreak areas and continue to use it for three weeks after travel in case they might be infected but not sick.

The U.S. women's national soccer team held two meetings to discuss the virus with doctors while in Texas for its Olympic qualifying tournament. Two players, Amy Rodriguez and Sydney Leroux, already had planned to take a break from the team for the Rio Games because of pregnancy.

Goalkeeper Hope Solo first raised questions in an interview with Sports Illustrated, suggesting she wouldn't do anything to jeopardize the health of her child if she were to decide to start a family.

"If the Olympics were today, I would not go," Solo reiterated during the tournament. "Fortunately, the Olympics are six months away. So, I believe we have some time to get our doubts and questions answered."

The CDC says there is no evidence to suggest that Zika poses a risk of birth defects for future pregnancies. The virus remains in the blood of an infected person for only about a week.

Spanish wind surfing gold medallist Marina Alabau believes she contracted Zika while training in Rio in December. First she came down with a fever, then other symptoms arose.

"Then my whole body turned red and everything itched. Two days later, my joints started aching," she said. "First it was in the fingers, then my wrists and finally my ankles. It was then that I decided to return to Spain because I was a little worried."

Alabau can't confirm her illness was Zika because she wasn't tested at the time. But she says the painful symptoms she suffered won't stop her from competing in the games in August.

At an event this week in Rio, 2012 Olympic diving silver medallist Abby Johnston pointed to another concern: The flu-like symptoms caused in some who contract the Zika virus can impact performance.

"That's really not what you would want, particularly for something you have trained your whole life for. To think that that could be taken away by a virus is pretty scary," said Johnston, a second-year medical student at Duke University.

The virus puts the International Olympic Committee, as well as national organizations and sports federations around the world, in the position of being educators to make sure athletes are armed with information about Zika and its risks. They were in a similar position for the 2008 Games, when poor air quality in Beijing raised concerns among athletes.

The Australian Olympic Committee has advised athletes to wear long sleeves and keep windows closed in the Olympic village, among other precautions.

U.S. Olympic Committee CEO Scott Blackmun sent a letter to all possible Olympians, acknowledging the growing worries over the virus. The USOC will hire two infectious disease specialists to advise potential Olympians who are worried about the Zika outbreak in Brazil.

"I want to emphasize that it is to us, as well, and that your well-being in Rio this summer is our highest priority," Blackmun wrote.

The IOC has expressed confidence in measures being taken against the virus in Brazil — spraying and removing standing water — and is following the advice of the World Health Organization. The IOC has distributed the guidance to all national Olympic committees.

"If you are a young woman who is pregnant, and not many athletes will be, or planning to get pregnant, then there are precautions you should take. Beyond that, for me it's a manufactured crisis," IOC member Dick Pound said.

Canadian heptathlete Brianne Theisen-Eaton, who is married to American decathlete Ashton Eaton, expressed what many athletes have voiced: As of now, they are going.

"I've had people say, 'If it was me, I wouldn't go. It's just not worth the risk.' I'm like, 'Do you understand how long I've been training for this? It's easy for you to say,"' Theisen-Eaton said. "Of course, of course, if they were saying we don't know the health implications later, yes, I would have a very tough decision to make."