The changing epidemiology and distribution of dengue in African countries: A scoping review

Protocol and registration

Scoping reviews are designed to systematically and comprehensively survey the literature on a broad subject area.^[17] While they do not include quality assessments of the included studies, scoping reviews employ a thorough and structured approach to explore the range and nature of research within a specific field. We conducted our scoping review following a predetermined protocol, adhering to established methods for scoping studies as outlined in the literature on systematic reviews^[18] and in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines for scoping reviews (PRISMA-ScR).^[19]

Eligibility criteria

The inclusion criteria used for this study include prospective studies, retrospective, cross-sectional, and case reports that focus on dengue studies reporting on the prevalence, incidence, or distribution of dengue in African countries, Articles examining factors contributing to the spread of dengue in new areas within Africa, research on the impact of climate change on the distribution and frequency of dengue outbreaks, comparative studies on the spread of dengue in urban versus rural areas in Africa and peer-reviewed articles, reports, and grey literature published in English. We excluded studies focusing solely on dengue epidemiology outside of Africa, articles on general mosquito control not specific to dengue, editorials, opinion pieces, and non-English publications. The inclusion and exclusion criteria that were applied to assess the eligibility of articles are shown in Table 1.

Search strategy

We conducted a comprehensive search to identify relevant studies on the epidemiology and distribution of dengue fever in African countries. The following databases were searched: PubMed, Scopus, and Google Scholar. The search was limited to articles published between January 2010 and May 2024. PubMed search string includes (“Dengue” [Mesh] OR “Dengue virus” OR “Dengue fever” OR “Aedes aegypti”) AND (epidemiology OR prevalence OR incidence OR distribution) AND (Africa OR “African countries”) AND (“climate change” OR “urban” OR “rural” OR “environmental factors”). Scopus search includes (TITLE-ABS-KEY [dengue OR “dengue fever” OR “dengue virus”]) AND (TITLE-ABS-KEY [epidemiology OR prevalence OR incidence OR distribution]) AND (TITLE-ABS-KEY [Africa OR “African region”]) AND (TITLE-ABS-KEY [“climate change” OR urban OR rural]). Google Scholar typically yields a very large number of records with inconsistent indexing. To ensure reproducibility, the search was restricted to the first 200 results sorted by relevance using the following string: “Dengue” AND “Africa” AND (“epidemiology” OR “prevalence” OR “distribution”) AND (“climate change” OR “urban” OR “rural”). The titles and abstracts retrieved from Google Scholar were screened manually to remove duplicates and non-peer-reviewed sources unless they met criteria for grey literature.

Screening and study selection process

All identified articles were uploaded into Covidence (Veritas Health Innovation, Melbourne, Australia; accessible at www.covidence.org), which is a specialized software designed to assist with systematic reviews. This platform facilitated the organization and screening of search results. Initially, two independent reviewers conducted a screening of the titles and abstracts of the articles to determine their compliance with the inclusion criteria. Any differences in opinion were reconciled by involving a third reviewer. Following the initial screening, the articles that passed this phase were subjected to a thorough full-text review by the same two reviewers to ensure that each met all the inclusion criteria, particularly emphasizing the necessity for a systematic search approach within the studies. Discrepancies during this phase were similarly resolved through consultation with a third reviewer. This structured approach ensured a rigorous and unbiased selection of studies for inclusion in the review.

Data extraction

Data extraction was conducted using a single standardized extraction form developed in Covidence. This form was used to systematically collect all relevant information from each included study. The extracted items included:

The extracted details included bibliographic data such as the article’s title, authors, and publication year;^[20] contextual information covering the article’s objectives, review type, diseases studied with specific attention to dengue (noted as either a primary or secondary focus), and the geographical area of study; the main findings of the study, specifically focusing on evidence of climate change effects on disease emergence, transmission, or spread, as well as any noted policy responses, interventions, or adaptive measures.^[21]

Data synthesis

The extracted data were synthesized to provide a comprehensive overview of the epidemiology and distribution of dengue fever in African countries. Descriptive statistics and thematic analysis were used to summarize the prevalence/incidence data to identify common factors contributing to the spread of dengue and the impact of climate change.

Reporting

The findings of the scoping review were reported following the PRISMA-ScR guidelines. This ensured transparency and reproducibility of the review process.

Characteristics of included studies

A total of 1301 records were identified through a database search of Scopus (651), PubMed (390) and Google Scholar (260). After the removal of duplicates, 641 records remained. From these, 409 were excluded due to several factors, such as the focus on dengue epidemiology outside Africa. Articles centered on general mosquito control not specific to dengue, editorial and opinion pieces and non-English publications. During the full-text article assessment, 162 articles were excluded resulting in 70 studies included in our analysis [Figure 1].

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Figure 1:

Flow chart of the study selection process.

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Selected variable from reported studies

The study types included 35 prospective studies (50.0%), 17 (24.2%) retrospective, 12 (17.1%) cross-sectional, and 6 (8.6%) case reports. The location of the included studies on reporting includes multiple region studies (28.7%), Central Africa (21.4%), East Africa (17.1%), West Africa (14.3%), North Africa (11.4%), and Southern Africa (7.1%). The Dengue serotype prevalence in the included study includes DENV-2 (27.1%) and DENV-1 (25.7%), respectively; mixed serotype also accounts for 17.2%. More than half of the studies used the clinical method only (54.3%) to select eligible participants, followed by 25.7%, which used laboratory methods such as immunoglobulin M/immunoglobulin G or reverse transcription polymerase chain reaction and 20.0%, who used both methods. Contrarily, the most frequent method of confirming dengue infection was through laboratory testing (70.0%), followed by the combination of both clinical and laboratory methods (14.3%) and then clinical methods (12.9%). This is depicted in Table 2 below.

Historical and current prevalence of dengue in different African countries

Among the 20 publications included in this section, a significant majority of the research articles (n=13, 65.0%) predicted an increase in the prevalence of dengue in the future. In contrast, a smaller proportion (n=7, 35.0%) projected a decline. Similarly, a significant majority of the studies (n=12, 60.0%) indicated that the areas conducive to the presence of Aedes aegypti, the mosquito species linked to dengue outbreaks, will expand. The projected rise in these figures was specifically anticipated in central, eastern, and south-eastern Africa. The remaining studies (n = 8, 40.0%) projected that there would be more losses than gains in terms of habitat range across southwestern and northern Africa.

Factors contributing to the spread and emergence of dengue in new areas

The primary risk factor, as determined by the majority of the included studies (n = 12, 48.0%), for the spread and establishment of dengue in new areas was the lack of effective mosquito control strategies. In addition, research has found that sociodemographic factors are associated with an increased risk of the illness. These characteristics include a lack of knowledge about the disease and its treatment approaches (n = 4, 16.0%), certain occupations (n = 3, 12.0%), advancing age (n = 1, 4.0%), and living in low-income areas (n = 3, 12.0%). Ecological factors, including climate, were identified as risk factors in 2 of the 20 studies included in this category (n = 2, 8.0%).

Impact of climate change on the geographic distribution and frequency of dengue outbreaks

The impact of climate change on the distribution of dengue fever was assessed in 17 included studies. Four out of the 17 (n = 4, 24.0%) studies concluded that climate change, such as temperature and rainfall, is affecting the prevalence and incidence of dengue outbreaks, compared to 3 (n = 3, 12.0%) studies that did not find such a relationship. Some studies (n = 3, 18.0%) concluded that based on the current climatic conditions, areas with low climatic suitable for A. aegypti in relation to dengue fever incidence was mainly found in northern and southern Africa, while high-to-moderate suitability areas were predicted for Western and part of central Africa. Most of the studies (n = 8, 47.0%) highlighted these African countries such as Kenya, Ethiopia, Angola, Madagascar, Mozambique, Chad, South Sudan, Niger, and Guinea will become more suitable for infectious A. aegypti in relation to dengue incidence in the future due to climate change.

Comparative analysis of urban versus rural spread of dengue

Eight studies highlighted the prevalence of dengue in urban areas, attributing this to the highly dense population present in these areas and also poor sanitation cultures in these areas.

The remaining studies focused on the spread of dengue in rural areas; several factors, such as lower socioeconomic conditions, lack of access to healthcare, and insufficient public health infrastructure, were mentioned.

Implications for public health

The growing suitability of African environments for A. mosquitoes has several implications for disease control. Weak vector management systems, fragmented surveillance, and inadequate diagnostic facilities may delay outbreak detection, allowing sustained transmission. Strengthening entomologic surveillance and integrating climate-based early warning systems would improve preparedness. In addition, targeted health education, urban sanitation improvements, and investments in laboratory diagnostic capacity could significantly reduce misdiagnosis and under-reporting. Understanding circulating serotypes is also critical because secondary infections with different serotypes increase the risk of severe disease. The continued predominance of DENV-1 and DENV-2 suggests the need for enhanced genomic and serotype monitoring to detect shifts that may influence disease severity or outbreak patterns.

Data gaps

Limitations

Scoping reviews strive to provide a comprehensive summary of the available literature. However, this is typically accomplished by omitting a full assessment of individual features, which may result in the removal of detailed findings or specific interventions mentioned in more specialist studies. Furthermore, there is the possibility of publication bias, in which studies with positive outcomes are more likely to be published than those with negative or inconclusive results, and could cause a slight misinterpretation of the overall findings.