Co-circulation of Dengue Virus Serotypes 1 and 3 during the 2019 epidemic in Dar es Salaam, Tanzania

BackgroundDengue is an important mosquito-borne viral disease in tropical and sub-tropical countries. In this study molecular characterization was carried out to determine dengue viruses circulating among patients at health facilities during 2019 epidemic in Dar es Salaam, Tanzania.\n\nMethodsThe study involved outpatients seeking care for febrile illness at four health facilities in Kinondoni and Ilala Districts of Dar es Salaam City in Tanzania. A total of 45 sera from the outpatients were confirmed dengue-positive for dengue virus (DENV) non-structural protein 1 (NS1) antigen and/or NS1-IgG/IgM antibodies using on-site rapid test. The presence of the virus was detected by reverse-transcription polymerase chain reaction (RT-PCR) method. Of the 45 sera, 20 samples were selected randomly for identification of specific dengue virus serotypes using RT-PCR followed by evaluation of resulting amplicons on agarose gel electrophoresis.\n\nFindings and significanceBoth Dengue virus serotypes 1 (DENV-1) and 3 (DENV-3) were detected in the samples tested with the former being dominant. We present the first evidence of dengue virus co-infection of DENV-1 and DENV-3 serotypes in Tanzania. The emergence of DENV-1 indicates the possibility of importation of the virus to Tanzania from endemic countries. Due to DENV serotype co-circulation, there is an increased risk of severe dengue in future epidemics. Our findings advocate the importance of genomic-based surveillance to provide rapid evidence of dengue virus emergence/re-emergence and spread.\n\nAuthor SummaryDengue viruses are the most important mosquito-borne pathogens that pose a serious global health threat. Tanzania has reported several dengue virus epidemics since 2010 with the majority of the epidemics occurring in Dar-es-Salaam city. Until August 2019, a total of 6,859 dengue cases have been confirmed in the country. We performed molecular characterization of dengue viruses (DENV) circulating during the 2019 epidemic phase. It was found that DENV-1 serotype was dominant during the epidemic and two samples of the tested sera were co-infected by DENV-1 and DENV-3 serotypes. These findings emphasize the importance of genomic-based surveillance of dengue viruses in Tanzania to guide strategies for appropriate interventions.