Analysis of a Dengue Virus Outbreak in Rosso, Senegal 2021

Abstract

Senegal is hyperendemic for dengue. Since 2017, outbreaks have been noticed annually in many regions around the country, marked by the co-circulation of DENV1-3. On 8 October 2021, a Dengue virus outbreak in the Rosso health post (sentinel site of the syndromic surveillance network) located in the north of the country was notified to the WHO Collaborating Center for arboviruses and hemorrhagic fever viruses at Institut Pasteur de Dakar. A multidisciplinary team was then sent for epidemiological and virologic investigations. This study describes the results from investigations during an outbreak in Senegal using a rapid diagnostic test (RDT) for the combined detection of dengue virus non-structural protein 1 (NS1) and IgM/IgG. For confirmation, samples were also tested by real-time RT-PCR and IgM ELISA at the reference lab in Dakar. qRT-PCR positive samples were subjected to whole genome sequencing using nanopore technology. Virologic analysis scored 102 positives cases (RT-PCR, NS1 antigen detection and/or IgM) out of 173 enrolled patients; interestingly, virus serotyping showed that the outbreak was caused by the DENV-1, a serotype different from DENV-2 involved during the outbreak in Rosso three years earlier, indicating a serotype replacement. Nearly all field-tested NS1 positives samples were confirmed by qRT-PCR with a concordance of 92.3%. Whole genome sequencing and phylogenetic analysis of strains suggested a re-introduction in Rosso of a DENV-1 strain different to the one responsible for the outbreak in the Louga area five years before. Findings call for improved dengue virus surveillance in Senegal, with a wide deployment of DENV antigenic tests, which allow easy on-site diagnosis of suspected cases and early detection of outbreaks. This work highlights the need for continuous monitoring of circulating serotypes which is crucial for a better understanding of viral epidemiology around the country.

Dengue 1 outbreak in Rosso, northern Senegal, October 2021: entomologic investigations

“…The Maximum Likelihood (ML) tree (Fig. 4) revealed that all the sequences obtained during this entomological investigation belonged to DENV-1/Genotype V and to the same clade as determined for samples from human cases detected in Rosso during this outbreak (Dieng et al 2022). Interestingly strains from this cluster were different from strains sequenced during previous DENV-1/Genotype V outbreaks in Senegal which occurred in the Louga area.…”

“…Molecular serotyping confirmed DENV-1 as the etiologic agent of this outbreak, suggesting that DENV-1 replaced DENV-2, that was responsible for the 2018 outbreak in Rosso (Dieng et al 2022). The introduction of this new serotype combined with other factors such as the increasing urbanization of Rosso and the strong presence of Ae.…”

“…During this entomological survey, which was carried out at the same time as the epidemiological studies, 107 suspected cases were recorded, 102 of which were confirmed as DENV (Dieng et al 2022).…”

“…Sequencing and phylogenetic analysis. Confirmed DENV-1-positive samples were subjected to genome sequencing as previously described by Dieng et al(2022). Briefly, RNA samples were subjected to cDNA synthesis using Lunascript RT supermix kit (New England Biolab, County Road, Ipswich, MA, USA) according to the manufacture's recommendations.…”

Insecticide resistance status of Aedes aegypti and Aedes albopictus mosquitoes in southern Benin, West Africa

“…albopictus in Nigeria since 1971. Recently, 238 and 380 confirmed cases of dengue fever have been recorded in Senegal and Côte d'Ivoire, respectively [ 22 , 23 ]. To plan an effective and sustainable control strategy against arbovirus vectors in Benin, there is an urgent need to determine the susceptibility level of Ae.…”