Many parts of Brazil also feature a very warm climate, crowded living conditions and poor sanitation — all conditions under which the Aedes mosquito thrives, Evans said.

“You can imagine the water and sanitation systems in the underdeveloped regions of Brazil might leave more room for mosquitoes to breed,” she said. “That may have been the kindling that lit the fire.”

Quoted in Zika: Why Brazil, Why Now, MedicineNet.com August 4, 2016