Epidemiology of Chikungunya infection on Reunion Island, Mayotte, and neighboring countries.

Since 2004, the frequency of chikungunya virus infections has been increasing in Africa, Indian Ocean islands, and Asia. The epidemic began on the Kenyan coast, and reached the Comoros at the end of 2004 before spreading to the South-western Indian Ocean islands (SWIOI) in 2005 and especially in 2006. The epidemic then spread to Asia where epidemic foci are still active today. This increase also affected temperate zone countries where imported cases were reported, and indigenous transmission was reported in Italy in 2007, and in France (Var) in 2010. This review provides an update on the knowledge gained from monitoring chikungunya infections in SWIOI. Despite significant differences in design and performance, the implementation of surveillance systems has allowed describing the evolution of epidemic waves in the affected areas. Synchronous epidemic waves were observed in SWIOI, despite the differences between the preventive measures locally implemented. Between 2005 and 2007, all SWIOI were in inter-epidemic situation, except for Madagascar where a persistent virus circulation in an endemic-epidemic pattern was observed. In 2009, and in 2010, two moderate indigenous outbreaks were identified on the Reunion Island by the inter-epidemic surveillance system. Strains analyses demonstrated a reintroduction of the virus from Madagascar. These limited outbreaks should be a reminder of the vulnerability of SWIOI to arbovirosis, since the entomological indexes for competent vectors are high and the virus keeps on circulating more or less actively in the area.