Chikungunya fever is a viral disease transmitted to human beings by Aedes genus mosquitoes. From 1972 to 1986 in Kédougou, Senegal, 178 Chikungunya virus strains were isolated from gallery forest mosquitoes, with most of them isolated from Ae. furcifer-taylori (129 strains), Ae. luteocephalus (27 strains), and Ae. dalzieli (12 strains). The characteristics of the sylvatic transmission cycle are a circulation periodicity with silent intervals that last approximately three years. Few epidemics of this disease have been reported in Senegal. The most recent one occurred in 1996 in Kaffrine where two Chikungunya virus strains were isolated from Ae. aegypti. The retrospective analysis of viral isolates from mosquitoes, wild vertebrates, and humans allowed to us to characterize Chikungunya virus transmission cycles in Senegal and to compare them with those of yellow fever virus.

As part of monitoring programs for yellow fever, dengue, and Rift Valley fever in Senegal, arboviruses not specifically studied are often isolated. These include Ngari, Chikungunya, Wesselsbron, Zika, and West Nile viruses. These wild vertebrate arboviruses, in equilibrium in their natural environment, can spread in human populations. For that reason, they represent a potential or real threat to public health as shown by fatal cases of infection with West Nile virus in Romania and by isolation of Ngari virus from humans in Senegal. 1, 2 Chikungunya virus is an Alphavirus of the family Togaviridae. It was first isolated by Ross in 1953 during a dengue epidemic that occurred in the Newala district of Tanzania. 3 Following 2–4 days of incubation, clinical symptoms include fever, headache, nausea, vomiting, photophobia, and arthralgia. Its association with fatal hemorrhagic forms was reported in India. 4 It is transmitted by mosquitoes, mainly of the genus Aedes. Its geographic distribution covers tropical regions of sub-Saharan Africa, Asia, and South America. In Senegal, three epidemics of Chikungunya fever were reported in 1966, 1982, and 1996 (Thonnon J, unpublished data) in the western part of the country. 5–7 Chikungunya virus was also isolated from different mosquito species. This study describes the occurrence of Chikungunya virus in Senegal after 25 years of entomologic monitoring and its transmission cycles.