Chikungunya outbreak in eastern Senegal, 2023

BACKGROUND: Chikungunya virus (CHIKV) is a mosquito-borne Alphavirus that has caused several epidemics around the world in recent years. CHIKV is endemic in eastern Senegal, particularly in Kédougou, where epidemiological and virological surveillance is implemented in combination with the 4S network. In August 2023, an outbreak was reported in Kédougou, which rapidly spread to Tambacounda. Epidemiological and virological investigations were carried out in both regions by teams from the Institut Pasteur de Dakar, the WHO, the Africa CDC and the Senegalese Ministry of Health. METHODS: The team first visited residential areas of confirmed cases, then a definition of suspected cases including socio-demographic aspects and clinical signs was used in an active door-to-door search for other cases. The blood samples were tested for CHIKV infection by real-time RT-PCR and anti-CHIKV IgM ELISA. Continuous variables were described using mean ± SD or median (IQR), and categorical variables as percentages with 95% confidence intervals, with group comparisons via Pearson’s χ2 or Fisher’s exact test. Kruskal–Wallis tests assessed differences in age across case categories. A multivariate logistic regression (variables with p < 0.25 in bivariate analysis, manual topdown stepwise selection) was fitted, and model fit evaluated using the Hosmer–Lemeshow test with interaction terms retained at p < 0.05. RESULTS: Out of 1070 blood samples tested, 315 confirmed cases were identified, resulting in an infection rate of 29.4%. There were no deaths. Under 15 and 15–30 age groups, male gender, headache, myalgia, joint pain, asthenia, and retro-orbital pain were among the factors associated with these cases. CONCLUSIONS: The present study provides clinical and epidemiological characteristics of CHIKV-positive cases, emphasizing the large geographical extension of the epidemic. It outlines the largest chikungunya outbreak documented in Senegal to date, hypothesizes sylvatic transmission, and describes the changing epidemiologic profile of CHIKV. It also stresses that a One-Health strategy is of primary importance in effectively controlling zoonoses.