The virus is spread by the same daytime-feeding mosquitoes that transmit dengue fever. The symptoms it causes are fever and joint pain and there is no vaccine to prevent or medicine to treat infection.
Six sub-counties of Mombasa and one in the district of Kilifi have reported suspected cases but the highest numbers are in Likoni and Mvita. There have been more than 450 suspected cases since the outbreak began in mid-December.
As there is no vaccine, preventing infection relies on avoiding mosquito bites. Advice to travellers is to apply an insect repellent containing an active ingredient, such as DEET, Picaridin or oil of lemon eucalyptus/PMD, to all exposed skin when outdoors.