Epidemiology of dengue fever in Gabon: Results from a health facility-based fever surveillance in Lambaréné and its surroundings

Molecular surveillance for dengue serotypes among the population living in Moyen-Ogooué province, Gabon; evidence of the presence of dengue serotype 1

BACKGROUND

Despite dengue virus (DENV) outbreak in Gabon a decade ago, less is known on the potential circulation of DENV serotypes in the country. Previous studies conducted in some areas of the country, are limited to hospital-based surveys which reported the presence of some cases of serotype 2 and 3 seven years ago and more recently the serotype 1. As further investigation, we extend the survey to the community of Moyen Ogooué region with the aim to assess the presence of the dengue virus serotypes, additionally to characterize chikungunya (CHIKV) infection and describe the symptomatology associated with infections.

METHOD

A cross-sectional survey was conducted from April 2020 to March 2021. The study included participants of both sexes and any age one year and above, with fever or history of fever in the past seven days until blood collection. Eligible volunteers were clinically examined, and blood sample was collected for the detection of DENV and CHIKV using RT-qPCR. Positive samples were selected for the target sequencing.

RESULTS

A total of 579 volunteers were included. Their mean age (SD) was 20 (20) years with 55% of them being female. Four cases of DENV infection were diagnosed giving a prevalence of 0.7% (95%CI: 0.2-1.8) in our cohort while no case of CHIKV was detected. The common symptoms and signs presented by the DENV cases included fatigue, arthralgia myalgia, cough, and loss of appetite. DENV-1was the only virus detected by RT-qPCR.

CONCLUSION

Our results confirm the presence of active dengue infection in the region, particularly DENV-1, and could suggest the decline of DENV-2 and DENV-3. Continuous surveillance remains paramount to comprehensively describe the extent of dengue serotypes distribution in the Moyen-Ogooué region of Gabon.

Mosquito-Borne Arboviruses Occurrence and Distribution in the Last Three Decades in Central Africa: A Systematic Literature Review

Arboviruses represent a real public health problem globally and in the Central African subregion in particular, which represents a high-risk zone for the emergence and re-emergence of arbovirus outbreaks. Furthermore, an updated review on the current arbovirus burden and associated mosquito vectors is lacking for this region. To contribute to filling this knowledge gap, the current study was designed with the following objectives: (i) to systematically review data on the occurrence and distribution of arboviruses and mosquito fauna; and (ii) to identify potential spillover mosquito species in the Central African region in the last 30 years. A web search enabled the documentation of 2454 articles from different online databases. The preferred reporting items for systematic reviews and meta-analyses (PRISMA) and the quality of reporting of meta-analyses (QUORUM) steps for a systematic review enabled the selection of 164 articles that fulfilled our selection criteria. Of the six arboviruses (dengue virus (DENV), chikungunya virus (CHIKV), yellow fever virus (YFV), Zika virus (ZIKV), Rift Valley fever virus (RVFV), and West Nile virus (WNV)) of public health concern studied, the most frequently reported were chikungunya and dengue. The entomological records showed >248 species of mosquitoes regrouped under 15 genera, with Anopheles (n = 100 species), Culex (n = 56 species), and Aedes (n = 52 species) having high species diversity. Three genera were rarely represented, with only one species included, namely, Orthopodomyia, Lutzia, and Verrallina, but individuals of the genera Toxorhinchites and Finlayas were not identified at the species level. We found that two Aedes species (Ae. aegypti and Ae. albopictus) colonised the same microhabitat and were involved in major epidemics of the six medically important arboviruses, and other less-frequently identified mosquito genera consisted of competent species and were associated with outbreaks of medical and zoonotic arboviruses. The present study reveals a high species richness of competent mosquito vectors that could lead to the spillover of medically important arboviruses in the region. Although epidemiological studies were found, they were not regularly documented, and this also applies to vector competence and transmission studies. Future studies will consider unpublished information in dissertations and technical reports from different countries to allow their information to be more consistent. A regional project, entitled "Ecology of Arboviruses" (EcoVir), is underway in three countries (Gabon, Benin, and Cote d'Ivoire) to generate a more comprehensive epidemiological and entomological data on this topic.

Distribution of Aedes mosquito species along the rural-urban gradient in Lambaréné and its surrounding

BACKGROUND

Aedes albopictus and Aedes aegypti are known for their potential as vectors of dengue (DENV) and chikungunya (CHIKV) viruses. However, entomological surveys are mostly carried out during epidemics. In Gabon where outbreaks of both viruses have occurred, there is no vector control program targeting these arboviruses. Therefore, we assessed the presence of Aedes species along a rural-urban gradient in Lambaréné (Gabon) and its surroundings and determined ecological factors associated to their presence.

METHODS

An entomological survey was conducted in Lambaréné and its surrounding rural areas. Mosquitoes were collected with aspirators around human dwellings, and ecological and environmental data were collected from each study area. Morphological identification keys were used to identify Aedes species. RNA was extracted from pools of female mosquitoes and amplified by RT-qPCR to detect the presence of DENV and CHIKV.

RESULTS

Overall, the most common vector collected was Aedes albopictus (97%, 4236/4367 specimens), followed by Aedes aegypti (3%, 131/4367). Albopictus vectors was more abundant in the rural area (Wilcoxon signed-rank test, Z = 627, P = 0.043) than in the urban area. In the urban area, a higher number of mosquitoes (45%) were recorded in the economic zone (zone 3) than in the historical and administrative zones (zone 1 and 2). In the rural area, the proportions of species numbers were significantly higher along the south rural transect (92%) compared to the north rural transect (Wilcoxon signed-rank test, Z = 43, P ˂ 0.016). We also noted a high abundance of vectors in environments characterized by monocultures of Hevea brasiliensis (Hevea) and Manihot esculenta (cassava) (Kruskal-Wallis H-test, H = 25.7, df = 2, P < 0.001). Finally, no mosquito pools were positive for either DENV or CHIKV.

CONCLUSION

Aedes albopictus was the dominant vector across the study sites due to its high invasiveness capacity. This presence re-affirms the potential for local transmission of both DENV and CHIKV, as indicated previously by serological surveys conducted in our study area, even though no transmission was detected during the current study. These findings underscore the need for regular arbovirus surveillance in the study region, with the aim of supporting vector control efforts in the event of outbreaks.

Seroprevalence of Dengue and Chikungunya Virus Infections in Children Living in Sub-Saharan Africa: Systematic Review and Meta-Analysis

Dengue and chikungunya viruses are frequent causes of malarial-like febrile illness in children. The rapid increase in virus transmission by mosquitoes is a global health concern. This is the first systematic review and meta-analysis of the childhood prevalence of dengue and chikungunya in Sub-Saharan Africa (SSA). A comprehensive search of the MEDLINE (Ovid), Embase (Ovid), and Cochrane Library (Wiley) databases was conducted on 28 June 2019, and updated on 12 February 2022. The search strategy was designed to retrieve all articles pertaining to arboviruses in SSA children using both controlled vocabulary and keywords. The pooled (weighted) proportion of dengue and chikungunya was estimated using a random effect model. The overall pooled prevalence of dengue and chikungunya in SSA children was estimated to be 16% and 7%, respectively. Prevalence was slightly lower during the period 2010-2020 compared to 2000-2009. The study design varied depending on the healthcare facility reporting the disease outbreak. Importantly, laboratory methods used to detect arbovirus infections differed. The present review documents the prevalence of dengue and chikungunya in pediatric patients throughout SSA. The results provide unprecedented insight into the transmission of dengue and chikungunya viruses among these children and highlight the need for enhanced surveillance and controlled methodology.

Re-emergence of dengue, chikungunya, and Zika viruses in 2021 after a 10-year gap in Gabon

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DENV-1, CHIKV, and ZIKV were detected in Gabon in 2021.

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DENV appeared to switch to serotype 1 from serotype 2 and 3 since 2010.

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Aedes albopictus‒adapted CHIKV appears to circulate repeatedly in Central Africa.

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The recent Gabonese ZIKV strain was genetically different from the previous strain.

Mosquito-borne viral infections are a major concern in endemic areas, such as Africa. Although outbreaks have been reported throughout Africa, only a few surveillance studies have been conducted in Gabon since the outbreaks of dengue virus (DENV) and chikungunya virus (CHIKV) in 2010. Therefore, the current situation is unknown. This study aimed to investigate the presence of arboviruses, especially DENV (serotypes 1–4), CHIKV, and Zika virus (ZIKV), in Gabon, Central Africa. Between 2020 and 2021, we collected 1060 serum samples from febrile patients and screened them against viruses using reverse transcription-quantitative PCR. We detected two DENV serotypes 1 (DENV-1), one CHIKV, and one ZIKV, and subsequently analyzed the genome sequences. To determine the genetic diversity and transmission route of the viruses, phylogenetic analysis was performed using complete or partial genome sequences. The DENV-1 and CHIKV strains detected in this study were closely related to the previous Gabonese strains, whereas the recent ZIKV strain was genetically different from a strain detected in 2007 in Gabon. This study provides new genomic information on DENV-1, CHIKV, and ZIKV that were detected in Gabon and insight into the circulation of the viruses in the country and their introduction from neighboring African countries.

Arboviruses as an unappreciated cause of non-malarial acute febrile illness in the Dschang Health District of western Cameroon

Acute febrile illness is a common problem managed by clinicians and health systems globally, particularly in the Tropics. In many regions, malaria is a leading and potentially deadly cause of fever; however, myriad alternative etiologies exist. Identifying the cause of fever allows optimal management, but this depends on many factors including thorough knowledge of circulating infections. Arboviruses such as dengue (DENV) cause fever and may be underdiagnosed in sub-Saharan Africa where malaria is a major focus. We examined cases of fever in western Cameroon that tested negative for malaria and found 13.5% (13/96) were due to DENV, with 75% (9/12) of these being DENV serotype 2 infections. Two complete DENV2 genomes were obtained and clustered closely to recent isolates from Senegal and Burkina Faso. The seroprevalence of DENV in this region was 24.8% (96/387). Neutralizing antibodies to DENV2 were detected in all (15/15) seropositive samples tested. Chikungunya (CHIKV) is an arthritogenic alphavirus that is transmitted by Aedes mosquitoes, the same principal vector as DENV. The seroprevalence for CHIKV was 15.7% (67/427); however, CHIKV did not cause a single case of fever in the 96 subjects tested. Of note, being seropositive for one arbovirus was associated with being seropositive for the other (Χ² = 16.8, p<0.001). Taken together, these data indicate that Aedes-transmitted arboviruses are endemic in western Cameroon and are likely a common but underappreciated cause of febrile illness. This work supports the need for additional study of arboviruses in sub-Saharan Africa and efforts to improve diagnostic capacity, surveillance systems, and arbovirus prevention strategies.

Acute illness with fever is common but can be challenging for clinicians to manage, particularly in resource-limited settings. In sub-Saharan Africa, malaria is a major cause of fever, but other causes of fever are poorly documented or monitored, which impairs optimal medical care to patients and implementation of public health interventions to control leading causes of disease. Viruses transmitted by mosquitoes are a prevalent and expanding problem throughout the tropics and beyond; however, there is concern that these infections frequently go undetected in sub-Saharan Africa. We discovered a previously unrecognized outbreak of dengue virus in western Cameroon by testing remnant samples from over 400 patients that presented with fever. Our results indicate that dengue has circulated in this region for decades with little recognition. This study adds important information about causes of fever in sub-Saharan Africa and advocates for increasing investment in surveillance systems and prevention strategies for mosquito-borne viruses.