Analyzing Transmission Patterns of Two Dengue Virus Serotypes during the 2023 Outbreak in Mali, West Africa

Dengue fever, a vector-borne disease caused by four serotypes of dengue virus (DENV), ranges from asymptomatic to severe illness, including hemorrhagic fever and shock syndrome. A 2023 outbreak (August 2023-May 2024) in Mali affected six districts in Bamako, causing 1,422 confirmed cases with a 2.7% fatality rate. In this study, viral sequencing provided insights into the molecular epidemiology and transmission dynamics of this outbreak. From September to October 2023, 23 of 42 suspected cases detected through national dengue surveillance activities were tested using the pan-vertebrate virus metagenomics method (virome capture sequencing platform for vertebrate viruses [VirCapSeq-VERT]). Sequencing data were analyzed using the Rapid Identification of Microbes pipeline, and Bayesian phylogenetic inference with Monte Carlo methods was used to assess viral genomic evolution. Among 23 patients, 61% were male, and the median age was 37 years (range: 20-74). The most common symptoms were fever (93.1%), headache (56.5%), and asthenia (47.8%). The largest proportion experienced dengue with warning signs (65.2%), followed by dengue without warning signs (30.4%) and severe dengue (4.4%). The successful sequencing of 19 samples revealed dengue virus serotype 3 (DENV-3; genotype III) in 15 (65.21%) samples and dengue virus serotype 1 (DENV-1; genotype III) in 4 (17.39%) samples. The DENV-1 sequences were analogous to West African sequences, and the DENV-3 were clustered with West African, Asian, and Caribbean sequences. In this study of DENV in Mali, we offer insights into the molecular epidemiology of the virus and underscore the benefits of the genomic surveillance of arboviruses in West Africa.