On the right is the Aedes mosquito, which is responsible for transmitting the Zika virus. How the Zika virus got to Brazil is still under investigation, but several hypotheses exist.
Many public health officials are concerned that the upcoming 2016 Summer Olympics in Brazil could write the recipe for a global Zika pandemic. While an athletic event may yet unleash Zika virus from Brazil to the rest of the world, it is also possible that an athletic event introduced Zika to Brazil. A genomic analysis of the Zika virus published in Science sheds some light on how the Zika virus got to Brazil and its relation to the 2013 outbreak in French Polynesia (Zika virus in the Americas: Early epidemiological and genetic findings, 2016. Nuno Rodrigues Faria, et al.).
Zika virus was detected in Brazil for the first time in May of 2015. However, microcephaly Zika-associated cases were not discovered until November 2015. It is possible that the Zika virus was introduced into Brazil a year before the first confirmed cases, putting the virus's entry date sometime in 2014. Genomic analysis showed that the Brazilian Zika virus ancestral origin is likely linked with the Zika virus epidemic in French Polynesia. Between late 2013 and early 2014 Zika hit an estimated 20,000 people in the southeastern Asian islands. No Zika-associated birth defects were found at the time, but respective analysis found a high level of birth defects during this period although the link was never proven. The Zika epidemic in French Polynesia ended quickly, after just a few months it was gone. There has not been a confirmed case of Zika since April 2014 in French Polynesia.
The Zika virus is hypothesized to have come to Brazil from the Pacific Islands during one of several athletic events held in Brazil during 2013 and 2014. These include the 2014 FIFA World Cup, the 2014 Va’a canoe event in Rio De Janeiro, and the 2013 FIFA Confederations Cup. Although the introduction of Zika could have occurred at any of these events, there was a nearly 50% increase in airline passengers arriving from South Pacific countries with prior Zika epidemics to Brazil throughout 2013. These athletic events all likely contributed to this increase in Brazil-bound airline passengers. Thus, it may be more important to look at overall travel patterns rather than any single athletic event to determine the spot of viral origin.