Gaspary Mwanyika of the SACIDS Foundation for One Health, Sokoine University of Agriculture, Tanzania describes the importance of genomic characterization in the control of dengue
Dengue is the main mosquito-borne viral disease of public health. Worldwide, the disease affects about 400 million people, leading to more than 25,000 deaths each year. The overall prevalence of dengue infection in Africa is 14% with serotypes 1 and 2 being the leading causes of outbreaks on the continent. Combating dengue faces several challenges. Lack of vaccine against dengue viruses makes control of the disease more difficult, increasing the risk of transmitting the virus. The disease often presents with non-specific symptoms similar to other diseases such as malaria, yellow fever, zika, chikungunya, and flu, therefore rapid laboratory confirmation is needed for an accurate diagnosis. This underlines the need for improved differential diagnosis of feverish diseases on the continent. Vector control and early detection remain the most important strategies to prevent and control dengue.
Dengue in Tanzania
Before 2010, very little was known about dengue epidemiology in Tanzania and its impact was: underreported due to insufficient monitoring capacity and diagnosis. Since then, annual outbreaks of dengue have been reported in the city of Dar es Salaam, which has become the epicenter of outbreaks in Tanzania.
Studies in Tanzania show that dengue infections are common in both rural and urban communities. Misdiagnosis of dengue and co-infections with other febrile diseases such as malaria and chikungunya have also been reported in Tanzania.
Dengue virus exposure in different ecological zones of Tanzania
Population-based serological studies have reported the presence of dengue viruses in the human population throughout Tanzania, with the highest seroprevalence reported in the northeastern part of the country; with an overall prevalence of 16.1%. These findings suggest a widespread spread of the viruses and that a large proportion of exposed individuals are unlikely to be diagnosed through mainstream health care due to the lack of reliable rapid diagnostic tools. Therefore, it is important that surveillance and diagnostic platforms for dengue viruses in Tanzania are strengthened to improve early diagnosis, patient management and outcomes.
Dynamics of the circulation of dengue virus serotypes in Tanzania: a lesson for future response to outbreaks
Studies in Tanzania have shown that 1, 2 and 3 serotypes of dengue are common. Nevertheless, genomic characterization of circulating serotypes is not commonly performed. Using field-deployable Oxford nanopore MinION sequencing technology, a recent study confirmed for the first time active transmission of dengue serotype 1 during the 2019 outbreak.
The analysis indicates that there was a possible introduction of the dengue virus serotype 1 genotype V into Tanzania from a single source in Asia. These observations suggest that the introduction of new serotypes and/or genotypes into Tanzania may increase the risk of serious disease outbreaks in the future. This is because immunity to previous serotypes does not provide long-term cross-protection against subsequent infecting serotypes. These findings argue for the need for genomic characterization and surveillance of the viruses recovered from the human population in Tanzania.
Opportunities to improve point-of-care diagnosis of dengue
Studies show that rapid diagnostic tests show poor specificity due to inherent cross-reactivity that can lead to misdiagnosis of dengue infection. In a study in Tanzania, we characterized antigenic determinants on dengue virus envelope protein domain III using bioinformatics tools.
The domain III protein harbors serotype-specific antigenic determinants and induces strong neutralizing antibodies that make it a suitable biomarker to develop new diagnostic tools. In our study in Tanzania, we demonstrated that domain III proteins consist of conformational antigenic determinants that can be expressed in simple bacterial cells as potential targets to develop diagnostic nanobodies. The application of nanobody-based diagnostic tools can help improve diagnosis of dengue virus infection at the point of care and minimize misdiagnosis in other infections.
The risk of transmission and spread of dengue is inevitable in Tanzania
Dengue is common in various ecological zones of Tanzania, which can be partly attributed to the tropical climate and human activities that promote the presence and abundance of mosquito vectors near human habitats. The circulation of multiple dengue virus serotypes 1, 2 and 3 in Tanzania could lead to explosive outbreaks and an increased risk of serious diseases in the future.
Globalization resulting from international connectivity through massive human travel from epidemic and endemic countries makes the risk of dengue transmission and spread inevitable in Tanzania. Studies in Tanzania point to the need to characterize the genomes of the dengue virus to monitor the spread of new/emerging genotypes and to develop reliable point-of-care diagnostic tests that can provide rapid evidence of the disease outbreak to guide for public health interventions.
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© 2019. This work is licensed under CC-BY-NC-ND.
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