Reemergence of Sylvatic Dengue Virus in Southern Senegal, 2021

As part of the syndromic surveillance of fever in Senegal, the virology department at Institut Pasteur de Dakar (IPD) in collaboration with the Epidemiology Unit and the Senegalese Ministry of Health conducted syndromic surveillance of fever in Senegal. Sample are from all suspected arboviral infections patients attending any of the sentinel sites. Collected blood samples were sent on a weekly basis at WHOCC for arboviruses and hemorrhagic fever viruses for screening of seven medically important arboviruses, including dengue virus (DENV). From January to December 2021, 2010 suspected cases were received among them 124 for confirmed to be DENV+ by RT-qPCR attempt of serotyping led to the detection of atypical DENV case from Sare Yoba area (Kolda region) which is unable to be correctly assigned to a serotype by the available tools (TIB Molbiol Modular Dx Dengue typing kit). Performed genome sequencing et phylogenetic analysis leads to the identification of a sylvatic DENV-2 strain closely related to a virus previously detected in Guinee-Bissau in 2009. This finding constitutes proof of the contemporary circulation of DENV-2 strain belonging to the sylvatic cycle in addition to well-known epidemic strains; this adds a piece of complexity to dengue management in Senegal. Alarmingly, it calls for improved genomic surveillance of DENV to know the genetic diversity of circulating strains in order to strengthen future vaccination policies

General characteristics of the study cohort.

<p>General characteristics of the study cohort.</p

Map of the study area of Niakhar showing the villages studied and the snail sampling sites in the fresh-water ponds and backwaters.

<p>Map of the study area of Niakhar showing the villages studied and the snail sampling sites in the fresh-water ponds and backwaters.</p

Baseline <i>S</i>. <i>haematobium</i> infection, efficacy of three treatments of praziquantel and reinfection levels over three years in nine villages of the Niakhar study area.

<p>Baseline <i>S</i>. <i>haematobium</i> infection, efficacy of three treatments of praziquantel and reinfection levels over three years in nine villages of the Niakhar study area.</p

Baseline <i>S</i>. <i>haematobium</i> infection, efficacy of three treatments of praziquantel and reinfection levels over three years according to age group and sex.

<p>Baseline <i>S</i>. <i>haematobium</i> infection, efficacy of three treatments of praziquantel and reinfection levels over three years according to age group and sex.</p

Global results of the malacological survey in water bodies from 2011 to 2013 in the nine villages selected in the Niakhar study area.

<p>Global results of the malacological survey in water bodies from 2011 to 2013 in the nine villages selected in the Niakhar study area.</p

Analysis of a Dengue Virus Outbreak in Rosso, Senegal 2021

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