Another pathogen has jumped its traditional boundaries to begin what some fear is a march around the globe. This time the invader is a virus that causes chikungunya, a crippling and painful disease until now found only in the tropics. This summer, it sickened more than 160 people in and around two small villages in Italy. Chikungunya is transmitted by the Asian tiger mosquito (Aedes albopictus), a species that is taking the world by storm, and medical entomologists worry that the disease has the potential to follow the insect.
Chikungunya is rarely fatal but can cause severe fevers, headaches, fatigue, nausea, and muscle and joint pains. People started falling sick in Castiglione di Cervia and Castiglione di Ravenna--two small villages separated by a river in the province of Ravenna--in early July, says Antonio Cassone of the Istituto Superiore di Sanità (ISS), a national government lab in Rome. But because symptoms overlap with those of other diseases, such as the Toscana virus, it took a long time to get noticed, he says. Samples reached ISS on 27 August, and the virus was identified the next day.
Epidemiological detective work suggests that the index patient was a man who traveled to one of the villages and fell sick there, after having been infected in India. Isolation and sequencing of the virus is under way to confirm that theory, Cassone says. One patient, an 83-year-old man with severe previous medical problems, has died; more than 30 cases are still awaiting lab confirmation.
Chikungunya caused a massive outbreak at La Réunion, a French island in the Indian Ocean, as well as several nearby islands, in 2005 and 2006. (ScienceNOW, 17 February 2006). India, too, has been hit very hard in recent years. Several European countries had seen "imported" cases of chikungunya lately--that is, people who were infected elsewhere. But local transmission in Europe has never been observed before. "It's fascinating," says entomologist Paul Reiter of the Pasteur Institute in Paris, France.
It's too early to tell whether the virus now has a permanent foothold in Europe. New cases have slowed down to a trickle, says Cassone, in part because the mosquito population is dwindling. But the critical question is whether infected mosquitoes can survive the winter or pass on the virus to their offspring via their eggs, says Reiter. "If they can, we might see a rip-roaring epidemic next year," he says.
There are neither drugs nor vaccines against chikungunya, but the outbreak at La Réunion has triggered renewed interest in an old vaccine candidate developed in the 1980s by a U.S. Army lab in Fort Detrick, Maryland, that was later shelved. Scientists at three French government institutions are currently working on that vaccine, and new clinical trials might begin before the end of 2008, says epidemiologist Antoine Flahault, who chaired a French task force on chikungunya last year.