A new mosquito-borne virus that causes high fever and intense joint pain is rapidly gaining a foothold in the Caribbean.
There are currently more than 4,000 confirmed cases of the fast-spreading chikungunya virus, most in the French Caribbean islands of Martinique, Guadeloupe and St Martin.
Another 31,000 suspected cases have been reported across the region of scattered islands.
The often painful illness most commonly found in Asia and Africa was first detected in December in tiny St Martin.
It was the first time that local transmission of chikungunya had been reported in the Americas. Since then, it has spread to nearly a dozen other islands and French Guiana, an overseas department of France on the north shoulder of South America.
It is rarely fatal and most chikungunya patients recover within a week, but some people experience continuing joint pain.
There is no vaccine and it is spread by the pervasive Aedes aegypti mosquito that transmits dengue fever, a similar but often more serious illness.
The US Centres for Disease Control and Prevention (CDC) said it was closely monitoring the spread of the virus and has been advising travellers about how best to protect themselves.
It recommends use of mosquito repellant and sleeping in screened rooms. It is also closely watching for any signs of chikungunya in the US.
"To help prepare the United States for possible introduction of the virus, CDC has been working with state health departments to increase awareness about chikungunya and to facilitate diagnostic testing and early detection of any US cases," said Dr Erin Staples, a medical epidemiologist with the CDC.