Suscepibility of Anopheles gambiae sl and Culex quinquefasciatus to diverse insecticides in the city of N'Djamena.

Mosquito resistance to insecticides remains a major concern for vector control programs based on chemical methods. Hence, a thorough knowledge of vector susceptibility to products recommended for public health is required for effective vector control programs. In this study, we assessed the susceptibility of wild Anopheles gambiae sl and Culex quinquefasciatus populations from N'Djamena (Chad) to four insecticide classes recommended for public health. The study took place from July to October 2014. Following WHO guidelines, bioassays were performed on two- to four-day-old, non-engorged female mosquitoes of both species, collected in the field. The insecticides used were deltamethrin (0.05%), permethrin (1%), DDT (4%), bendiocarb (0.01%), and malathion (5%). Anopheles gambiae sl showed full susceptibility to bendiocarb and malathion but was resistant to pyrethroids; mortality rates were 2% for deltamethrin, 2% for permethrin, and 0% for DDT. Culex quinquefasciatus was susceptible to malathion but resistant to the other insecticides, with a mortality rate of 22% for deltamethrin, 29% for permethrin, 23% for DDT, and 45% bendiocarb. The resistance of Anopheles gambiae sl and of Culex quinquefasciatus may affect the population's adherence to the use of insecticide-treated mosquito nets. Malaria control programs are advised to extend insecticide resistance monitoring to the main culicide species that bite human populations.

[Retrospective study of cutaneous leishmaniasis in the district hospital of Am Timan, Chad]. / Étude rétrospective de la leishmaniose cutanée à l'hôpital de district d'Am Timan, Tchad.

Cutaneous leishmaniasis is not included in the statistical yearbook of Health of the Ministry of Public Health. The aim of our study was to describe the epidemiological profile of cases of cutaneous leishmaniasis attended at the District Hospital of Am Timan in order to assess the importance and the prevalence of this neglected disease. This is a retrospective study of cases reported in the records of the Laboratory of the Hospital District of Am Timan between January 2008 and December 2012. It allowed the identification of 680 clinical cases. Direct microscopic diagnosis was positive in 580 cases (85%). The number of cases has been increasing from 2008 to 2010 (2008 = 80 cases, 123 cases in 2009; 2010 = 198 cases) before decreasing during the following year (2011 = 137 cases and in 2012 = 42 cases). The months of strong incidence of the cases were June, July, August and September. The M/F sex-ratio was 1.7.

Genetic mapping identifies a major locus spanning P450 clusters associated with pyrethroid resistance in kdr-free Anopheles arabiensis from Chad.

Prevention of malaria transmission throughout much of Africa is dependent on bednets that are impregnated with pyrethroid insecticides. Anopheles arabiensis is the major malaria vector in Chad and efforts to control this vector are threatened by the emergence of pyrethroid resistance. WHO bioassays revealed that An. arabiensis from Ndjamena is resistant to pyrethroids and dichlorodiphenyltrichloroethane (DDT) but fully susceptible to carbamates and organophosphates. No 1014F or 1014S kdr alleles were detected in this population. To determine the mechanisms that are responsible for resistance, genetic crosses were established between the Ndja strain and an insecticide susceptible population from Mozambique. Resistance was inherited as an autosomal trait and quantitative trait locus (QTL) mapping identified a single major locus on chromosome 2R, which explained 24.4% of the variance in resistance. This QTL is enriched in P450 genes including 25 cytochrome P450s in total. One of these, Cyp6p4 is 22-fold upregulated in the Ndja strain compared with the susceptible. Piperonyl butoxide (PBO) synergist and biochemical assays further support a role for P450s in conferring pyrethroid resistance in this population.