Predicting tiger mosquito breeding sites through earth observation and statistical analysis

International audienceReunion Island is a densely populated French region of the Indian Ocean. There, the Asian Tiger mosquito, Aedes albopictus, is the main vector of arboviroses such as dengue and chikungunya. Recently, vector control services have been collecting in situ data on potential breeding sites covering about 10% of the districts of the island. This study investigates the capability of environmental features extracted from earth observation data to be used in predicting the distribution of potential breeding sites of Ae. albopictus in Reunion Island. Spectral indices (NDVI, NDWI and Brightness index) were calculated from a very-high spatial resolution Pléaides mosaic of 2020 images over the island, while data on the annual cumulative rainfall and the annual average temperature were obtained from the Météo-France / CIRAD network. Textural information over urban areas was also extracted from the Pléaides mosaic. Corresponding textural indices highlight different district typologies based on spatial arrangements between buildings and vegetation. For each district, we analyzed the correlations between i) the number of potential observed breeding sites and ii) the mean values of textural and spectral indices, as well as the mean precipitation and annual temperature, through both univariate and multivariate analysis; the most significant variables were eventually combined using a generalized linear model. We found that the correlation between those combined variables and in situ data on breeding sites of Ae. albopictus is significant. This statistical relationship makes it possible to use earth observation environmental variables as predictors of the number of potential breeding sites for all areas in the island

Predicting tiger mosquito breeding sites through earth observation and statistical analysis

International audienceReunion Island is a densely populated French region of the Indian Ocean. There, the Asian Tiger mosquito, Aedes albopictus, is the main vector of arboviroses such as dengue and chikungunya. Recently, vector control services have been collecting in situ data on potential breeding sites covering about 10% of the districts of the island. This study investigates the capability of environmental features extracted from earth observation data to be used in predicting the distribution of potential breeding sites of Ae. albopictus in Reunion Island. Spectral indices (NDVI, NDWI and Brightness index) were calculated from a very-high spatial resolution Pléaides mosaic of 2020 images over the island, while data on the annual cumulative rainfall and the annual average temperature were obtained from the Météo-France / CIRAD network. Textural information over urban areas was also extracted from the Pléaides mosaic. Corresponding textural indices highlight different district typologies based on spatial arrangements between buildings and vegetation. For each district, we analyzed the correlations between i) the number of potential observed breeding sites and ii) the mean values of textural and spectral indices, as well as the mean precipitation and annual temperature, through both univariate and multivariate analysis; the most significant variables were eventually combined using a generalized linear model. We found that the correlation between those combined variables and in situ data on breeding sites of Ae. albopictus is significant. This statistical relationship makes it possible to use earth observation environmental variables as predictors of the number of potential breeding sites for all areas in the island

Texture des images satellite et caractérisation des milieux urbains favorables aux moustiques vecteurs

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Modelling the Potential Human Exposure to Japanese Encephalitis Virus (JEV) in Case of Introduction into Reunion Island

International audienceJapanese encephalitis virus (JEV) is a vector-borne zoonotic virus and the leading cause of human acute encephalitis in Asia. Continuous human and commercial exchanges between Southeast Asia where JE is endemic and Reunion Island increase the risk of introducing JEV on the island, where putative vectors of JEV such as Culex quinquefasciatus and amplifying hosts such as pigs are present. Each of the 255 Reunionese pig farms was assumed to harbor a Cx. quinquefasciatus population and, together with the competent hosts: pigs and poultry and noncompetent hosts: humans, dogs, and cattle, located within a radius of 1 km, formed an epidemiological unit. We used a deterministic compartmental model to investigate whether these epidemiological units could be invaded by JEV in the event of an introduction. Since the vector population size changes seasonally, we computed the basic reproduction number (R0) using vector population sizes ranging from 100 to 100,000 vectors for each of the 255 epidemiological units. The size of the potentially exposed human population was calculated in the case where the virus would be introduced in a single epidemiological unit and in the extreme case where the virus would have spread over the whole island. For a vector population of 1,000 vectors per unit, 2 out of 255 units had an R0 ≥ 1. With 50,000 vectors per unit, more than 75% (193/255) of the units had an estimated R0 ≥ 1, representing a median of approximately 2,500 potentially exposed people if JEV was introduced in a single unit, and about 140,000 potentially exposed people if JEV had expanded throughout the island. The unit located a few kilometers from the large port area of Reunion Island had an estimated R0 ≥ 1 with at least 10,000 vectors, making it a potential gateway to JEV given a virus introduction of infected vectors

Could Sterile Aedes albopictus Male Releases Interfere with Aedes aegypti Population in Reunion Island?

International audienceIn Reunion Island, the feasibility of an Aedes albopictus control program using the Sterile Insect Technique (SIT) is studied. Because, in some regions, Ae. albopictus is living in sympatry with Aedes aegypti, the impact of releasing millions of sterile male Ae. albopictus on female Ae. aegypti reproduction needs to be assessed. Thus, to study the potential heterospecific matings, a marking technique using rhodamine B has been used. Rhodamine is given in solution to male mosquitoes to be incorporated into the male body and seminal fluid and transferred during mating into the bursa inseminalis and spermathecae of females. The presence of rhodamine in females occurred in 15% of cases when Ae. aegypti females were offered non-irradiated Ae. albopictus males, 5% when offered irradiated Ae. albopictus males and 18% of cases in the inverse heterospecific matings. Moreover, our results also showed that these matings gave few eggs but were not viable. Finally, the results showed that whatever the type of mating crosses, females in cages previously crossed with males of another species can re-mate with males of their species and produce an equivalent amount of egg compared to females only mated with conspecific males. Despite the promiscuity of the males and females in small cages for three days, heterospecific mating between sterile male Ae. albopictus and female Ae aegypti, 95% of the females have not been inseminated suggesting that in the field the frequency satyrization would be very low

Successes and failures of sixty years of vector control in French Guiana: what is the next step?

Since the 1940s, French Guiana has implemented vector control to contain or eliminate malaria, yellow fever, and, recently, dengue, chikungunya, and Zika. Over time, strategies have evolved depending on the location, efficacy of the methods, development of insecticide resistance, and advances in vector control techniques. This review summarises the history of vector control in French Guiana by reporting the records found in the private archives of the Institute Pasteur in French Guiana and those accessible in libraries worldwide. This publication highlights successes and failures in vector control and identifies the constraints and expectations for vector control in this French overseas territory in the Americas

Aedes albopictus Adult Medium Mass Rearing for SIT Program Development

International audienceFor the production of several hundred thousands of Aedes albopictus sterile males for the implementation of a Sterile Insect Technique (SIT) program, no costly mass-rearing equipment is needed during the initial phases, as optimized rearing at laboratory scale can be sufficient for the first steps. The aim of this study was to maximize the egg production by optimizing adult rearing methods for Ae. albopictus. The effect of parameters such as male/female ratio, density of adults, membrane type for blood feeding, quantity of blood delivered, continuous or discontinuous blood feeding, and surface of substrates for egg laying on overall egg production was tested to find optimized conditions. Based on the number of eggs produced per cage in response to the parameters tested, the optimum cage set-up was seen to be 1500 adults in a 30 × 30 × 30 cm cage with a male/female sex ratio of 1:3, fed by fresh bovine blood for periods of 30 min using a cellulose membrane covering a 10 cm stainless steel plate heated by a Hemotek device, and the provision of five oviposition cups to collect eggs. With this set-up, production per cage can reach a maximum of 35,000 eggs per week

Successes and failures of sixty years of vector control in French Guiana: what is the next step?

<div><p>Since the 1940s, French Guiana has implemented vector control to contain or eliminate malaria, yellow fever, and, recently, dengue, chikungunya, and Zika. Over time, strategies have evolved depending on the location, efficacy of the methods, development of insecticide resistance, and advances in vector control techniques. This review summarises the history of vector control in French Guiana by reporting the records found in the private archives of the Institute Pasteur in French Guiana and those accessible in libraries worldwide. This publication highlights successes and failures in vector control and identifies the constraints and expectations for vector control in this French overseas territory in the Americas.</p></div

Impact of selection regime and introgression on deltamethrin resistance in the arbovirus vector Aedes aegypti – a comparative study between contrasted situations in New Caledonia and French Guiana

International audienceBACKGROUNDPyrethroid insecticides such as deltamethrin have been massively used against Aedes aegypti leading to the spread of resistance alleles worldwide. In an insecticide resistance management context, we evaluated the temporal dynamics of deltamethrin resistance using two distinct populations carrying resistant alleles at different frequencies. Three different scenarios were followed: a continuous selection, a full release of selection, or a repeated introgression with susceptible individuals. The responses of each population to these selection regimes were measured across five generations by bioassays and by monitoring the frequency of knockdown resistance (kdr) mutations and the transcription levels and copy number variations of key detoxification enzymes.RESULTSKnockdown resistance mutations, overexpression and copy number variations of detoxification enzymes as a mechanism of metabolic resistance to deltamethrin was found and maintained under selection across generations. On comparison, the release of insecticide pressure for five generations did not affect resistance levels and resistance marker frequencies. However, introgressing susceptible alleles drastically reduced deltamethrin resistance in only three generations.CONCLUSIONThe present study confirmed that strategies consisting to stop deltamethrin spraying are likely to fail when the frequencies of resistant alleles are too high and the fitness cost associated to resistance is low. In dead-end situations like in French Guiana where alternative insecticides are not available, alternative control strategies may provide a high benefit for vector control, particularly if they favor the introgression of susceptible alleles in natural populations

Évaluation de la lutte anti-vectorielle à La Réunion

Citation suggérée : Anses. (2023). Évaluation de la stratégie de lutte anti-vectorielle (LAV) à La Réunion. (saisine n°2023-SA-0003). Maisons-Alfort : Anses, 53 p.La Réunion est une île volcanique de 2 512 km2 située au sud-ouest de l'océan Indien qui possède une population d’environ 850 000 habitants principalement localisée en zone urbaine le long du littoral. Bien que 12 espèces de moustiques appartenant aux genres Aedes, Anopheles, Culex et Orthopodomyia aient été décrites sur l'île, Ae. albopictus et Cx. quinquefasciatus sont les espèces les plus abondantes et se rencontrent couramment dans les zones urbaines, périurbaines et rurales, parfois jusqu'à 1 200 m d’altitude. Bien qu’Ae. aegypti était historiquement présente à La Réunion, cette espèce a été fortement impactée suite à l’arrivée compétitive d’Ae. albopictus avec seulement deux populations isolées subsistant aujourd’hui dans des ravines sur les communes de Saint-Joseph et de Trois Bassins.À La Réunion, jusqu’en 2006, les traitements de LAV étaient principalement basés sur l’utilisation du téméphos en traitement anti-larvaire puis remplacés par des traitements adulticides avec la deltaméthrine lors de l’épidémie de Chikungunya en 2005-2006 (forte intensité de traitements durant cette période).À partir de 2006, la LAV a essentiellement reposé sur une surveillance des vecteurs, une sensibilisation de la population et sur l’utilisation de la deltaméthrine comme adulticide (Aqua K-Othrine en pulvérisation spatiale) et du Bti comme larvicide. Jusqu’à 2012, le service de LAV de l’ARS Océan Indien (OI) est intervenu chez les particuliers à leur demande pour des désinsectisations péridomiciliaires dites de « confort » ou suite à l’identification, dans le cadre des actions de surveillance, d’indices stégomyiens1 élevés. À partir de 2012, l’ARS a engagé une démarche de réduction de la pression insecticide par ciblage des actions de traitement insecticides LAV traitements adulticides uniquement ciblés autour des cas de transmissions et arrêt des nébulisations spatiales de nuit à partir de 2020 - 2021).À partir de 2017, une circulation active et récurrente de la dengue est constatée dans l’île de La Réunion et les actions de LAV se sont centrées sur les actions de sensibilisation, de lutte mécanique, des traitements insecticides péridomiciliaires et des pulvérisations spatiales de nuit notamment dans les zones connaissant des foyers de dengue. Cette dernière pratique a été totalement suspendue en 2021 du fait d’une évaluation, effectuée au Laboratoire d’entomologie du Service LAV, très défavorable de son efficacité.Sur le plan épidémiologique, la première épidémie de dengue décrite à La Réunion est survenue en 1977-1978 et aurait touché environ 30% de la population. Depuis 2017, l’île de La Réunion connaît une circulation active récurrente de la dengue avec, de 2018 à 2021, la survenue de quatre épisodes épidémiques importants ; en 2021, près de 30 000 cas ont été biologiquement confirmés et la période épidémique s’est étalée sur une durée de 18 semaines.Depuis fin 2021, le niveau 4 du plan ORSEC-LAV , qui avait été activé en phase épidémique, a été maintenu à ce niveau sans correspondance avec la situation épidémiologique de la dengue, pour redescendre finalement au niveau 2A (circulation virale modérée autochtone) en juillet 202