“The clearest consequence is that you increase the risk of spreading the virus and the disease. With half-a-million people going to Rio for the Games – not just the usual visitors but people coming from every corner of the world – you open up the possibility of someone from each one of those places getting infected. Once the individual returns to his country, the local mosquitoes may then transmit the disease,” says Amir Attaran, a professor of epidemiology and public health at the University of Ottawa. Attaran co-authored the letter that more than 170 scientists have signed and sent to the World Health Organization (WHO) and the International Olympic Committee, urging them to postpone the upcoming Games – scheduled for August 5 to August 21 – until the Zika virus is no longer a threat. The letter also asks the organizations to consider moving the Games to another host country.