GENEVA - The World Health Organization (WHO) has played down concerns over the spread of the Zika virus, amid calls for the Rio Olympics in August to be postponed. Senior WHO official Bruce Aylward told the BBC that risk assessment plans were in place, and reiterated that there was no need to delay the Games. The mayor of Rio said disease-carrying mosquitoes were being eradicated. The officials were responding to an open letter by scientists saying it was "unethical" for the Games to go ahead. The letter also said the global health body should revisit its Zika guidance. The Zika virus is linked to severe birth defects. Between February and April, Brazil registered more than 90,000 likely cases of Zika. The number of babies born with Zika-linked defects stood at 4,908 in April. "Those are two of the exact measures that that group has asked for and that is exactly what is being done, and clearly we need to have better communicated that." The World Health Organization is key here. As long as it continues to reject pleas to cancel or move the Games from Rio, the IOC will feel confident. No contingency plans are being put in place should the doomsday scenario occur. And privately, the IOC seems more concerned by the doping crisis; allegations of state-sponsored cheating at the 2014 Sochi Games, and the question mark over the participation of Russian athletes in Rio, than it is by Zika. But if the WHO changes its tune, the IOC would be left facing one of the biggest challenges in its history. Two years ago, it had to bar young athletes from the Ebola-affected region of West Africa from participating in certain events at the Youth Olympic Games in Nanjing, China, to rule out infection. But this would be on a whole different scale.(FA)