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International audience; Yellow Fever (YF) remains a major public health issue in Sub-Saharan Africa and South America, despite the availability of an effective vaccine. In Africa, most YF outbreaks are reported in West Africa. However, urban outbreaks occurred in 2016 in both Angola and the Democratic Republic of Congo (DRC), and imported cases were reported in Chinese workers coming back from Africa. In Central Africa, Cameroon and the Republic of Congo host a high proportion of non-vaccinated populations increasing the risk of urban outbreaks. The main vector is Aedes aegypti and possibly, Aedes albopictus, both being anthropophilic and domestic mosquitoes. Here, we provide evidence that both Ae. aegypti and Ae. albopictus in Cameroon and the Republic of Congo are able to transmit Yellow fever virus (YFV) with higher rates of infection, dissemination, and transmission for Ae. aegypti. We conclude that the potential of both Aedes species to transmit YFV could increase the risk of urban YF transmission and urge public health authorities to intensify their efforts to control domestic vectors, and extend vaccine coverage to prevent major YFV outbreak.

Yellow fever is a vector-borne disease endemic in tropical regions of Africa, where 90% of the global burden occurs, and Latin America. It is notoriously under-reported with uncertainty arising from a complex transmission cycle including a sylvatic reservoir and non-specific symptom set. Resulting estimates of burden, particularly in Africa, are highly uncertain. We examine two established models of yellow fever transmission within a Bayesian model averaging framework in order to assess the relative evidence for each model’s assumptions and to highlight possible data gaps. Our models assume contrasting scenarios of the yellow fever transmission cycle in Africa. The first takes the force of infection in each province to be static across the observation period; this is synonymous with a constant infection pressure from the sylvatic reservoir. The second model assumes the majority of transmission results from the urban cycle; in this case, the force of infection is dynamic and defined through a fixed value of R0 in each province. Both models are coupled to a generalised linear model of yellow fever occurrence which uses environmental covariates to allow us to estimate transmission intensity in areas where data is sparse. We compare these contrasting descriptions of transmission through a Bayesian framework and trans-dimensional Markov chain Monte Carlo sampling in order to assess each model’s evidence given the range of uncertainty in parameter values. The resulting estimates allow us to produce Bayesian model averaged predictions of yellow fever burden across the African endemic region. We find strong support for the static force of infection model which suggests a higher proportion of yellow fever transmission occurs as a result of infection from an external source such as the sylvatic reservoir. However, the model comparison highlights key data gaps in serological surveys across the African endemic region. As such, conclusions concerning the most prevalent transmission routes for yellow fever will be limited by the sparsity of data which is particularly evident in the areas with highest predicted transmission intensity. Our model and estimation approach provides a robust framework for model comparison and predicting yellow fever burden in Africa. However, key data gaps increase uncertainty surrounding estimates of model parameters and evidence. As more mathematical models are developed to address new research questions, it is increasingly important to compare them with established modelling approaches to highlight uncertainty in structures and data., Author summary Yellow fever (YF) is notoriously under reported due to non-specific symptom spectrum and the true burden is highly uncertain as a result of a complex transmission cycle. As such, estimates surrounding YF burden are highly uncertain and the mechanisms behind transmission are often unclear. We assess these mechanisms and the resulting uncertainty by estimating two existing models of YF transmission within a product space framework. This allows us to produce updated estimates of transmission intensity and to compare the relative support for each model given the data. We find strong support for a model assuming a static force of infection, approximating the constant infection pressure from the sylvatic reservoir of YF. We also highlight areas where data is sparse, often the same areas estimated to have especially high transmission intensity. This is the first robust multi-model approach to applied YF modelling and provides a framework that could be extended to other disease models.

The production of a large number of mosquitoes of high biological qualities and reliable sex sorting before release are key challenges when applying the sterile insect technique as part of an area-wide integrated pest management approach. There is a need to fully evaluate the production capacity of the equipment developed in order to plan and maintain a daily production level for large-scale operational release activities. This study aimed to evaluate the potential use of the FAO/IAEA larval rearing unit for Aedes aegypti and the subsequent female contamination rate after sex sorting with a Fay-Morlan glass separator. Trays from each rack were tilted and their contents sorted either for each individual tray or after mixing the content of all trays from the rack. The pupal production and the female contamination rate were estimated with respect to day of collection, position of the tray, type of pupae collection, and sorting operator. Results showed significant daily variability of pupal production and female contamination rate, with a high male pupal production level achieved on the second day of collection and estimated female contamination of male pupae reached around 1%. Neither tray position nor type of pupae collection affected the pupal production and female contamination rate. However, the operator had a significant effect on the female contamination rate. These results highlight the need to optimize pupal production at early days of collection and to develop a more effective and automated method of sex separation.Développement larvaire et production de pupes d’Aedes aegypti dans le système d’élevage de masse de la FAO/AIEA et facteurs influençant l’efficacité de la séparation des sexes.La production d’un grand nombre de moustiques de haute qualité biologique et le tri des sexes avant les lâchers sont des défis clés lors de l’application de la technique des insectes stériles, dans le cadre d’une approche de lutte intégrée contre les ravageurs à l’échelle d’une zone. Il est nécessaire d’évaluer pleinement la capacité de production des équipements développés afin de planifier et de maintenir un niveau de production quotidien pour les activités de libération opérationnelle à grande échelle. Cette étude visait à évaluer l’utilisation potentielle de l’unité d’élevage larvaire FAO/AIEA pour Aedes aegypti et le taux de contamination par des femelles après le tri sexuel avec un séparateur en verre Fay–Morlan. Les plateaux de chaque rack ont été inclinés et leur contenu trié soit pour chaque plateau, soit après avoir mélangé le contenu de tous les plateaux du rack. La production de pupes et le taux de contamination par des femelles ont été estimés en fonction du jour de collecte, de la position du bac, du type de collecte des pupes et de l’opérateur du tri. Les résultats ont montré une variabilité quotidienne significative de la production de pupes et du taux de contamination par des femelles, avec un niveau élevé de production de pupes mâles atteint le deuxième jour de collecte et la contamination estimée des pupes mâles par des femelles a atteint environ 1 %. Ni la position du plateau ni le type de collecte des pupes n’ont affecté la production de pupes et le taux de contamination par des femelles. Cependant, l’opérateur avait un effet significatif sur le taux de contamination par les femelles. Ces résultats mettent en évidence la nécessité d’optimiser la production des pupes dès les premiers jours de la collecte et de développer une méthode de séparation des sexes plus efficace et automatisée.

Background Aedes-borne diseases as dengue, zika, chikungunya and yellow fever are an emerging problem worldwide, being transmitted by Aedes aegypti and Aedes albopictus. Lack of up to date information about the distribution of Aedes species hampers surveillance and control. Global databases have been compiled but these did not capture data in the WHO Eastern Mediterranean Region (EMR), and any models built using these datasets fail to identify highly suitable areas where one or both species may occur. The first objective of this study was therefore to update the existing Ae. aegypti (Linnaeus, 1762) and Ae. albopictus (Skuse, 1895) compendia and the second objective was to generate species distribution models targeted to the EMR. A final objective was to engage the WHO points of contacts within the region to provide feedback and hence validate all model outputs. Methods The Ae. aegypti and Ae. albopictus compendia provided by Kraemer et al. (Sci Data 2:150035, 2015; Dryad Digit Repos, 2015) were used as starting points. These datasets were extended with more recent species and disease data. In the next step, these sets were filtered using the Köppen–Geiger classification and the Mahalanobis distance. The occurrence data were supplemented with pseudo-absence data as input to Random Forests. The resulting suitability and maximum risk of establishment maps were combined into hard-classified maps per country for expert validation. Results The EMR datasets consisted of 1995 presence locations for Ae. aegypti and 2868 presence locations for Ae. albopictus. The resulting suitability maps indicated that there exist areas with high suitability and/or maximum risk of establishment for these disease vectors in contrast with previous model output. Precipitation and host availability, expressed as population density and night-time lights, were the most important variables for Ae. aegypti. Host availability was the most important predictor in case of Ae. albopictus. Internal validation was assessed geographically. External validation showed high agreement between the predicted maps and the experts’ extensive knowledge of the terrain. Conclusion Maps of distribution and maximum risk of establishment were created for Ae. aegypti and Ae. albopictus for the WHO EMR. These region-specific maps highlighted data gaps and these gaps will be filled using targeted monitoring and surveillance. This will increase the awareness and preparedness of the different countries for Aedes borne diseases. Electronic supplementary material The online version of this article (10.1186/s12942-018-0125-0) contains supplementary material, which is available to authorized users.

The sterile insect technique is a promising environmentally friendly method for mosquito control. This technique involves releasing laboratory-produced sterile males into a target field site, and its effectiveness may be affected by the extent of adult mosquito predation. Sterile males undergo several treatments. Therefore, it is vital to understand which treatments are essential in minimizing risks to predation once released. The present study investigates the predation propensity of four mantis species (Phyllocrania paradoxa, Hymenopus coronatus, Blepharopsis mendica, Deroplatys desiccata) and two gecko species (Phelsuma standingi, P. laticauda) on adult Aedes aegypti, Ae. albopictus and Anopheles arabiensis mosquitoes in a laboratory setting. First, any inherent predation preferences regarding mosquito species and sex were evaluated. Subsequently, the effects of chilling, marking, and irradiation, on predation rates were assessed. The selected predators effectively preyed on all mosquito species regardless of the treatment. Predation propensity varied over days for the same individuals and between predator individuals. Overall, there was no impact of laboratory treatments of sterile males on the relative risk of predation by the test predators, unless purposely exposed to double the required sterilizing irradiation dose. Further investigations on standardized predation trials may lead to additional quality control tools for irradiated mosquitoes.