The patient showed up at the University of Miami Jackson Memorial Hospital feverish and hobbled by joint pain, a rash spreading across her face, and was presumed to be suffering from lupus or severe rheumatoid arthritis.

But in talking to the middle-aged woman last week, doctors realized that her symptoms and recent history of travel to the Dominican Republic added up to a different diagnosis: chikungunya, an infectious disease carried by the same mosquitoes that spread dengue fever.

Chikungunya (pronounced chick-un-GOON-ya) has plagued other parts of the world—particularly Asia and Africa—for decades, becoming more prevalent in recent years. But it arrived in the Caribbean only in December and has already infected as many as 250,000 people there.

The virus is