What began with just 10 confirmed cases of the chikungunya virus on the French side of St. Martin last month has quickly spiraled into a much larger outbreak with nearly 300 confirmed cases spanning the Caribbean from Martinique to the British Virgin Islands.

With more than 200 “probable or confirmed cases,” St. Martin remains the epicenter of the outbreak, though there have been four-dozen more cases on Martinique and another two-dozen on Saint Barts, according to the European Centre for Disease Prevention and Control. Health officials in Dominica, Guadeloupe and French Guiana also reported cases of chikungunya virus, which can cause severe joint pain, fever and headaches. The case in French Guiana is of particular concern because it could mean that the virus has reached the South American mainland.

More than 100 laboratory-confirmed cases of chikungunya were identified in the United States between 1995 and 2009, but none of the infected contracted the disease in the Western Hemisphere. All but three of the cases occurred between 2006 and 2009 with travelers to India and Indian Ocean Islands, where there were large outbreaks of the disease.

While outbreaks of chikungunya have been documented across Africa, Europe, Asia and the Pacific, the cases in the Caribbean mark the first time the disease has been reported among non-travelers in the Western Hemisphere, the Centers for Disease Control and Prevention noted in a warning issued last month. It said the affected St. Martin residents had not traveled abroad recently, suggesting that the chikungunya virus was present in island populations of mosquitoes and being spread locally.

“Microbes know no boundaries, and the appearance of chikungunya virus in the Western Hemisphere represents another threat to health security,” CDC Director Tom Frieden said in a statement. “CDC experts have predicted and prepared for its arrival for several years and there are surveillance systems in place to help us track it. To protect Americans, we have to support and maintain capacity to detect and respond to the emergence of new viruses."

CDC said it had been working since 2006 with the Pan American Health Organization to prepare for the arrival of chikungunya in the Americas, and conducted a planning workshop for 22 Caribbean countries to increase awareness. It noted that while there is no vaccine and no specific treatment for the infection, chikungunya is rarely fatal and those who endure it are thought to confer lifelong immunity.

Chikungunya is similar to the more common dengue virus, which has historically been a much bigger problem in Caribbean. The World Health Organization documented about 79,000 cases of dengue last year, including 141 deaths (most of which occurred in the Dominican Republic).

The same mosquitoes that spread the dengue virus also carry chikungunya. Known by the scientific names of Aedes aegypti and Aedes albopictus, these mosquitoes are found throughout the Caribbean, the tropics and parts of the southern United States.

Like dengue, symptoms of chikungunya include fever, joint and muscle pain, headache and rash -- all of which last for about a week and begin between four and seven days after the bite of an infected mosquito. In rare cases, some patients experience long-term joint pain.

CDC advised anyone returning from the Caribbean with such conditions to seek immediate medical assistance.

The Caribbean is one of the most tourism-dependent regions in the world, and a dramatic decrease in visitors could have devastating effects on the region’s economy. While officials in Europe, the United States and South America have issued alerts over the virus, none have called for their citizens to avoid the region altogether.

Rather, health officials advised tourists to the Caribbean to take several steps to protect themselves against mosquito bites, like wearing long sleeves and pants, purchasing insect repellent and using air conditioning and screens on windows and doors to keep mosquitoes out.