Science Magazine (Internet / Print) 02/24/06 A French island in the Indian Ocean is reeling from an explosive outbreak of a little-known viral disease. On 17 February, the French National Institute for Public Health Surveillance said that an estimated 110,000 residents of Réunion, population 770,000, had been infected with the chikungunya virus--almost 22,000 of them between 6 and 12 February alone. Chikungunya, which is spread by mosquitoes, is rarely fatal--of 52 patients who died, all but one were suffering from other diseases as well--but it can cause high fevers, rashes, and excruciating joint and muscle pains. "It's a massive outbreak, it's absolutely alarming," says Stephen Higgs of the University of Texas Medical Branch in Galveston, one of a few dozen researchers around the world who study chikungunya, a member of the alphavirus genus that also includes rarities such as eastern equine encephalitis and western equine encephalitis.