A new study shows the Zika virus was circulating in Haiti in 2014, long before it became obvious that it was spreading in Brazil, NBC News reported. 

The team checked out three mysterious infections in Haiti caused by the Zika virus. Their study raises questions about when and how Zika arrived in the Americas.

"We know that the virus was present in Haiti in December of 2014," said Dr. Glenn Morris, a professor of medicine and the director of the University of Florida's Emerging Pathogens Institute. "And, based on molecular studies, it may have been present in Haiti even before that date." 

Earlier this year, international experts used a "genetic clock" to show the Zika virus has changed. And it very closely matches a strain that circulated in French Polynesia in 2013. What's not clear is why it's now being seen to cause disease. Tests show it has mutated, but it's not yet clear if the mutations somehow make it more virulent.