While the disease, called chikungunya, usually is not fatal, the epidemic has overwhelmed hospitals, cut economic productivity and caused its sufferers days of pain and misery. And the count of victims is soaring.
In El Salvador, health officials report nearly 30,000 suspected cases, up from 2,300 at the beginning of August, and hospitals are filled with people with the telltale signs of the illness, including joint pain so severe it can be hard to walk.
"The pain is unbelievable," said Catalino Castillo, a 39-year-old seeking treatment at a San Salvador hospital. "It's been 10 days and it won't let up."
Venezuelan officials reported at least 1,700 cases as of Friday, and the number is expected to rise. Neighboring Colombia has around 4,800 cases but the health ministry projects there will be nearly 700,000 by early 2015. Brazil has now recorded its first locally transmitted cases, which are distinct from those involving people who contracted the virus while traveling in an infected area.