BackgroundThe 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.MethodsMosquito 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.ResultsAnopheles 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.ConclusionsThere 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.

Leishmaniasis transmitted by sandflies is an important vector-borne disease. In Chad, information on sandflies is outdated, and so this study was designed to update the sandfly fauna. Sandflies were collected in five health districts representing two geoclimatic zones using sticky traps and pyrethrum sprays in indoor and peridomestic habitats between September 2019 and December 2020. All collected sandfly specimens were identified based on species-level morphological characters. A total of 2,015 specimens belonging to 13 species of sandflies (one Phlebotomus and twelve Sergentomyia) were collected and identified. The vector of human cutaneous leishmaniasis, Phlebotomus duboscqi, represents 0.65% of all collected sandflies and is the only representative of the Phlebotomus genus to be collected predominantly inside human dwellings. Phlebotomus orientalis, the vector of visceral leishmaniasis previously collected in Chad in 1976 was not found in this study. Sergentomyia clydei, Sergentomyia schwetzi, Sergentomyia antennata and Sergentomyia africana were the most abundant species collected with 44.71%; 22.73%; 16.03% and 11.17%, respectively. Sergentomyia schwetzi and Sergentomyia dubia, the two species involved in the transmission of canine leishmaniasis, were found in five and four study sites respectively. According to our results, the sandfly fauna of the two geoclimatic zones of Chad is comprised of 13 species. Our data showed that, unlike P. orientalis which was not found, P. duboscqi is present in four of the five sites surveyed. Therefore, these areas are at risk and remain potential foci of cutaneous leishmaniasis. However, the need for further studies such as vector species detection, their seasonal fluctuations and their vector competence.

In underdeveloped countries, infectious diseases remain one of the most important public health challenges. Visceral leishmaniasis, also known as Kala-azar, is a lethal vector-borne parasitic disease with an increasing number of cases. However, it remains one of the most neglected diseases in the world. It is the most severe form of leishmaniasis and is endemic in 75 countries. Around 95% of the patients live in seven countries: Brazil, Ethiopia, India, Kenya, Somalia, South Sudan, and causes about 20,000-40,000 deaths per year of which 50-70% are children. In Central Africa, this pathology is little known and less documented, making it difficult to access information. We have performed this study to characterize the knowledge on the epidemiology of visceral leishmaniasis in Central Africa. We reviewed the literature on visceral leishmaniasis in Central Africa on the number of reported cases, identified parasites, reservoirs and vectors. The documents consulted came from WHO reports, publications of scientific journals, reports of research institutions and abstracts of scientific conferences consulted online on Pubmed and Google Scholar. The information covers the period from the first reporting of cases in each country until December 2020. The review of the situation of visceral leishmaniasis revealed that it is not a significant public health problem in Central Africa. However, a lot of work remains to be done especially surveillance and research in order to present the exact situation of the disease in this part of the continent. This work would include the underreporting of cases inherent to the weaknesses of the surveillance system in these countries, the clarification of the transmission dynamics of human visceral leishmaniasis, canine leishmaniasis, the identity of parasites and vectors.

Introduction: Leishmaniasis transmitted by sandflies is an important vector-borne disease. In Chad, information on sandflies is outdated, and so this study was designed to update the sandfly fauna. Methods: Sandflies were collected in five health districts representing two geoclimatic zones using sticky traps and pyrethrum sprays in indoor and peridomestic habitats between September 2019 and December 2020. All collected sandfly specimens were identified based on species-level morphological characters. Results: A total of 2,015 specimens belonging to 13 species of sandflies (one Phlebotomus and twelve Sergentomyia) were collected and identified. The vector of human cutaneous leishmaniasis, Phlebotomus duboscqi, represents 0.65% of all collected sandflies and is the only representative of the Phlebotomus genus to be collected predominantly inside human dwellings. Phlebotomus orientalis, the vector of visceral leishmaniasis previously collected in Chad in 1976 was not found in this study. Sergentomyia clydei, Sergentomyia schwetzi, Sergentomyia antennata and Sergentomyia africana were the most abundant species collected with 44.71%; 22.73%; 16.03% and 11.17%, respectively. Sergentomyia schwetzi and Sergentomyia dubia, the two species involved in the transmission of canine leishmaniasis, were found in five and four study sites respectively. Conclusion: According to our results, the sandfly fauna of the two geoclimatic zones of Chad is comprised of 13 species. Our data showed that, unlike P. orientalis which was not found, P. duboscqi is present in four of the five sites surveyed. Therefore, these areas are at risk and remain potential foci of cutaneous leishmaniasis. However, the need for further studies such as vector species detection, their seasonal fluctuations and their vector competence.