Clément Kerah-Hinzoumbé

Le but de lenquête était d'identifier les vecteurs de chikungunya et d’étudier leur bioécologie afin de contribuer aux activités de riposte contre l’épidémie de 2020 dans les villes d’Abéché et de Biltine à l’Est du Tchad. Les stades immatures des moustiques Aedes ont été collectés et les indices de risque épidémique (indices Récipient, Maison et de Breteau) ont été calculés et comparés par le test du Khi carré. Les larves et nymphes collectées ont été mises en élevage et les adultes qui en sont issus ont été identifiés morphologiquement à l'aide d'une clé dichotomique. La faune résiduelle endophile a été échantillonnée par pulvérisation matinale d'insecticide dans les chambres où seules les femelles étaient collectées. Au total, 2 039 spécimens de moustiques appartenant à trois genres ont été collectés : 470 (23%) ont été identifiés comme Aedes aegypti, 731 Anopheles spp (36%) et 838 Culex spp (41%). Les pots de fleurs étaient les gîtes les plus représentés (69%) suivis des jarres/fûts d'eau (17%) et des pneus/récipients abandonnés (14%). Partout, les indices de risque étaient largement au-dessus des seuils épidémiques définis par l’OMS. Entre les deux villes, seul l'indice Maison a présenté une différence significative (p=0,004) : il était plus élevé à Abéché qu’à Biltine. L'enquête a permis d'identifier A. aegypti comme vecteur probable de chikungunya présent dans les deux villes. Il importe de chercher à comprendre ses comportements de piqûre et de repos ainsi que sa sensibilité aux différentes classes d'insecticides afin d'organiser une lutte antivectorielle efficace.

Introduction: malaria is a major public health issue in Africa. In Chad in 2019, with 955,243 confirmed cases and 2,955 deaths, malaria is the main cause of consultations. A longitudinal entomological study was conducted in Moissala Health District. Its objective was to assess the impact of indoor residual spraying with 80% bendiocarb wettable powder on malaria transmission. Methods: two areas were defined for the study: Dembo, located in the sprayed area, Moissala, in the untreated area. Two sampling methods were used: pyrethrum spray catches and human landing catches. Results: sixteen sessions of human landing catches totalling 32 man-nights were conducted and 160 rooms/site were sprayed. Two anopheles were captured in Dembo and 547 in Moissala. In Moissala, An coluzzii, An funestusand An rufipeswere captured in the rooms and on human bait. An colluzziiand An funestuswere captured in pyrethrum spray catches in Dembo. The anophelian human landing catches density was zero in Dembo while it was 8.38 bites/man/night in outdoor and 10.06 bits/man/night in indoor in Moissala. Only An coluzziiwas found infected in human landing catches and sporozoite index of was 7.46% (10/134) in outdoor and 7.45% (12/161) in indoor in Moissala. Malaria transmission was estimated at 0.53 infected bites/man/night in outdoor and 0.75 infected bites/man/night in indoor i.e. 229.95 infected bites/man/year in outdoor and 273.75 infected bites/man/year. In pyrethrum spray catches, An coluzziiand An rufipeswere the two species found infected in Moissala with sporozoite indices of 6.70% (23/343) and 20% (2/10) respectively. However, in Dembo, neither of the two captured mosquitoes was found infected. Conclusion: the indoor residual spraying campaign in the eastern zone of Moissala has led to the collapse of vectors' density and aggressiveness. However, its evaluation over a short period of time is not sufficient to assess the impact of malaria transmission in this constant and endemic malaria zone.

BackgroudMalaria is a major public health and development problem in Africa. In Chad in 2016, with 720 765 confirmed cases and 1 686 deaths, malaria is the main cause of consultations, hospitalizations and deaths in health facilities. A longitudinal entomological study was carried out from 07 to 24 December 2016 in the Moïssala health district. The objective of the study was to assess the impact of malaria transmission one year after two cycles of indoor residual spraying of 80% bendiocarb wettable powder (Ficam WP 80 W).MethodsTwo areas were defined for the study: the town of Dembo, located in the sprayed area, was chosen as the test town and Moïssala, located in the untreated area, was chosen as the control town. Two sampling methods were used: collection of resting endophilic fauna and direct capture of aggressive mosquitoes from human subjects. ResultsA total of 16 sessions of catches on human subjects totalling 32 man-nights were conducted and 160 rooms were sprayed per site. For 160 sprayed chambers per site, two anopheles were captured in Dembo compared to 547 in Moïssala. Three anophelian species have been morphologically identified. In Moïssala, An gambiae sl (An colluzzii : 96%, An gambiae : 4%), An funestus and An rufipes were captured at rest in the rooms and on human bait. In Dembo, the two anopheles, An colluzzii and An funestus were captured at rest in the rooms. On human bait as in endophilic fauna, An gambiae sp was the most common species in Moïssala. The aggressive anophelian density was zero in Dembo while it is 9 bites per man per night in Mosesala. Only Anopheles gambiae sp was found infected in aggressive wildlife. The sporozoite index of the aggressive fauna of An gambiae sp was 7.45%. Malaria transmission was estimated at 0.67 infected bites per man per night, or 244.55 infected bites per man per year. In endophilic fauna, An gambiae sp and An rufipes were the two species found infected in Moïssala with sporozoite indices of 6.70% (23/343) and 20% (2/10) respectively. However, in Dembo, neither of the two captured individuals was found infected.ConclusionsThe indoor residual spraying campaign in the eastern zone of the Moïssala health district has led to the collapse of the density and aggressiveness of malaria vectors. However, its evaluation over a short period of time is not sufficient to assess the impact of malaria transmission in this stable and highly endemic malaria zone.

Background: The Sahel region of Chad Republic is a prime candidate for malaria pre-elimination. To facilitate pre-elimination efforts in this region, two populations ofAnopheles coluzziifrom Central Chad Republic were characterized, their insecticide resistance profile and the possible molecular mechanisms driving the resistance in the field investigated.Methods: Bloodfed femaleAnopheles gambiaes.l. resting indoor, were collected at N’djamena and Massakory, Chad in 2018 and characterized for species composition, and infection rate was determined using the TaqMan assay. Susceptibility to various insecticides was assessed using WHO tube bioassays. Cone bioassays were conducted using various long-lasting insecticidal nets (LLINs). Results were analysed using Chi Square test. Knockdown resistance (kdr) andace-1markers were investigated by TaqMan genotyping.Results: Anopheles coluzziiwas the major vector found in N’djamena (100%) and Massakory (~ 94%). NoPlasmodiumwas found in 147 bloodfed F₀An. coluzzii(82 from N’djamena and 65 from Massakory).High intensity pyrethroid resistance was observed with mortalities of < 2% for permethrin, deltamethrin and etofenprox, and with < 50% and < 60% dead following exposure to 10× diagnostic doses of deltamethrin and permethrin, respectively. For both sites, < 10% mortalities were observed with DDT. Synergist bioassays with piperonylbutoxide significantly recovered pyrethroid susceptibility in Massakory populations, implicating CYP450s (mortality = 13.6% for permethrin,χ² = 22.8, df = 1,P = 0.0006; mortality = 13.0% for deltamethrin,χ² = 8.8, df = 1,P < 0.00031). Cone-bioassays established complete loss of efficacy of the pyrethroid-based LLINs; and a 100% recovery of susceptibility following exposure to the roof of PermaNet®3.0, containing piperonylbutoxide. Both populations were susceptible to malathion, but high bendiocarb resistance was observed in Massakory population. The absence oface-1mutation points to the role of metabolic resistance in the bendiocarb resistance. Both 1014F and 1014S mutations were found in both populations at around 60% and < 20% respectively. Sequencing of intron-1 of the voltage-gated sodium channel revealed a low genetic diversity suggesting reduced polymorphism.Conclusions: Multiple resistance inAn. coluzziipopulations from Chad highlight challenges associated with deployment of LLINs and indoor residual spraying (IRS) in the Sahel of this country. The pyrethroid-synergists LLINs (e.g. PermaNet®3.0) and organophosphate-based IRS maybe the alternatives for malaria control in this region.

The development and spread of insecticide resistance among malaria vectors, is a threat to the continued effectiveness of interventions to control and eliminate the disease. The status of insecticide resistance among malaria vector populations at two sites in Kome, southern Chad, was evaluated to inform decisions on vector control. Mosquito larvae were collected from temporary rain-filled and semi-permanent breeding places at two sites and reared in a laboratory. Emerging Anopheles gambiae (senso lato) (s.l.) adults were morphologically identified, sorted and evaluated for susceptibility to WHOPES recommended insecticides. Standardized biomolecular and biochemical methods were used to determine sibling species and molecular forms: knockdown resistant alleles (kdr-w) for pyrethroids and DDT; acetylcholinesterase-1 resistant alleles for organophosphate and carbamates; biochemical resistance through measurement of the levels of non-specific esterase (α and β), oxidase and glutathione-s-transferases activities. Anopheles gambiae (s.l.) was the main vector group in the two study sites and comprised of Anopheles gambiae (senso stricto) (s.s.) and An. arabiensis, respectively, at 71 and 29 % in Site A, and 60 and 40 % at Site B. Anopheles gambiae (s.s.) was composed of M (Anopheles coluzzii) and S [nominotypical An. gambiae (s.s.)] molecular forms. Anopheles coluzzii accounted for over 98 % of the sub-group. There was extensive phenotypic resistance to pyrethroids, DDT and carbamates, but full susceptibility to organophosphates. Population-wide frequency of knockdown resistant allele in An. gambiae (s.l.) was 43 homozygous (RR), 19 heterozygous (RS) and 38 % homozygous susceptible (SS). When segregated by species and molecular forms, An. coluzzii had the highest kdr-w frequency of 37.4 homozygous resistant alleles, and 17.5 % heterozygous, with 8.3 % homozygote susceptible alleles. An. gambiae (s.s.) had 1 % homozygous resistant allele. Levels of esterase, oxidase and glutathione-s-transferases were not significantly different compared to fully susceptible laboratory raised An. gambiae (s.s.) Kisumu reference, although few individuals showed significant elevation of esterases (> 0.04 μg/protein), indicating a likely start of biochemical enzyme resistance. There is an urgent need for action to stop and reverse significant insecticide resistance in the area. A comprehensive entomological surveillance and monitoring program is needed to understand the full extent of resistance to enable realistic insecticide resistance management strategy, and also to track future changes in the vector populations.

Insecticide resistance in malaria vectors is a growing concern in many countries which requires immediate attention because of the limited chemical arsenal available for vector control. The current extent and distribution of this resistance in many parts of the continent is unknown and yet such information is essential for the planning of effective malaria control interventions.

Pyrethroid insecticides are widely used for insect pest control in Cameroon. In certain insect species, particularly the malaria vector Anopheles gambiae, resistance to this class of insecticides is a source of great concern and needs to be monitored in order to sustain the efficacy of vector control operations in the fields. This study highlights trends in DDT and pyrethroid resistance in wild An. gambiae populations from South Cameroon.

Knowledge of some baseline entomological data such as Entomological Inoculation Rates (EIR) is crucially needed to assess the epidemiological impact of malaria control activities directed either against parasites or vectors. In Chad, most published surveys date back to the 1960's. In this study, anopheline species composition and their relation to malaria transmission were investigated in a dry Sudanian savannas area of Chad.

Indoor residual spraying and insecticide-treated nets (ITN) are essential components of malaria vector control in Africa. Pyrethroids are the only recommended compounds for nets treatment because they are fast-acting insecticides with low mammalian toxicity. However, there is growing concern that pyrethroid resistance may threaten the sustainability of ITN scaling-up programmes. Here, insecticide susceptibility was investigated in Anopheles gambiae sensu lato from an area of large scale ITN distribution programme in south-western Chad.