The suspected culprit is a mosquito-borne virus called Zika. Officials in Colombia, Ecuador, El Salvador and Jamaica have suggested that women delay becoming pregnant. And the Centers for Disease Control and Prevention has advised pregnant women to postpone travel to countries where Zika is active.
Zika virus was discovered almost 70 years ago, but wasn’t associated with outbreaks until 2007. So how did this formerly obscure virus wind up causing so much trouble in Brazil and other nations in South America?
Where did Zika come from?
Zika virus was first detected in Zika Forest in Uganda in 1947 in a rhesus monkey, and again in 1948 in the mosquito Aedes africanus, which is the forest relative of Aedes aegypti. Aedes aegypti and Aedes albopictus can both spread Zika. Sexual transmission between people has also been reported.
Zika has a lot in common with dengue and chikungunya, another emergent virus. All three originated from West and central Africa and Southeast Asia, but have recently expanded their range to include much of the tropics and subtropics globally. And they are all spread by the same species of mosquitoes.
Until 2007 very few cases of Zika in humans were reported. Then an outbreak occurred on Yap Island of Micronesia, infecting approximately 75 percent of the population. Six years later, the virus appeared in French Polynesia, along with outbreaks of dengue and chikungunya viruses.
How did Zika get to the Americas?
Genetic analysis of the virus revealed that the strain in Brazil was most similar to one that had been circulating in the Pacific.
Brazil had been on alert for an introduction of a new virus following the 2014 FIFA World Cup, because the event concentrated people from all over the world. However, no Pacific island nation with Zika transmission had competed at this event, making it less likely to be the source.