In Chad, data on the diversity and distribution of sandflies are dated. The first inventory of the sandfly fauna, which combined the work of Abonnec and other researchers with that of Lewis and Hitchcock, collected a total of 15 sandfly species [17].
Even though 15 species of sandflies were previously recorded in Chad, during this study only 13 species were collected. Furthermore, five sandfly species that were previously collected were not found in this study (P. orientalis, P. bergeroti, S. murphyi, S. inermis and S. adleri,). Conversely, we collected three additional species that were never reported in Chad (S. dubia, S. schoutedeni, and S. fallax). The absence of species from the previous fauna and the appearance of species detected for the first time would be due either to collection method, misidentification, environmental disturbances of human or climatic origin leading to their disappearance, and to the migration of other species that have adapted and proliferated in their new environment.
P. duboscqi, already reported in Chad (in N'Djaména, Abéché and Ouarai), is the only representative of the genus Phlebotomus identified during this study and collected in four of the five districts, which could suggest that transmission of the disease is possible throughout the area. The range of distribution of this species is very wide. It extends from Senegal to Ethiopia through the Gulf of Guinea and the neighboring countries of Chad [18, 21–23]. This species is the vector of cutaneous leishmaniasis caused by Leishmania major in West and East Africa [24, 25] and is thought to be responsible for the cases of cutaneous leishmaniasis recorded in Chad [14, 15]. P. duboscqi was mostly collected inside human houses (76.9%). The presence of this species caught inside human houses was expected as it had already been recorded in Bamako [26] and central Mali [24]. Another epidemiologically important species of the genus Phlebotomus, Phlebotomus orientalis, a vector of visceral leishmaniasis in East African countries [27], already identified in Chad, was not found during our surveys, although it has been reported in countries bordering Chad, specifically Niger, Sudan and Nigeria [18, 21, 28]. The absence of this important species in our collections despite its reported presence in neighboring countries does not prove that this species does not exist but may be due to collection methods because in the survey that allowed its collection, light traps were used [17]. In Ethiopia, light traps were more effective in capturing this species than sticky traps and pyrethrin spraying combined [29].
Species of the genus Sergentomyia were almost predominant in the collections compared to the genus Phlebotomus with 99.35% of species identified. This predominance has already been observed in many surveys, notably in Chad [17], Nigeria [23], Cameroon [22] and Senegal [30]. Four species of this group (S. clydei, S. schwetzi, S. antennata and S. africana) were the most common and abundant both in the peridomestic environment and in human habitations. They represented 95% of all Sergentomyia captured. These species have a wide distribution in the Afrotropical zone, extending from West Africa to Ethiopia, much of East Africa [18] and are most often found in large numbers [21, 31]. The identification of DNA and/or parasites of Leishmania in several species of the genus Sergentomyia raise questions regarding their potential role in the circulation of mammalian leishmaniasis in the Old World and has draw general interest [32]. S. schwetzi, S. dubia and S. clydei, three of these species, whose epidemiological importance has been published, were collected during our survey, Indeed, S. schwetzi and S. dubia collected indoor rooms and in the peridomestic environment as in our study, had been found infected by Leishmania infantum and involved in the transmission of canine leishmaniasis in Mont-Rolland, Senegal [30].
During our collection, S. schwetzi was found in all five study sites while S. dubia was collected in four of the five sites. Thus, surveillance is necessary to avoid an epidemic and the establishment of an endemic focus of canine leishmaniasis in these areas in case of importation of the disease. In N'Djaména, since 1973, after six years of observation, the veterinary service identified Leishmania parasites in the smears of two infested dogs [8]. One of these two species would probably be at the origin of the transmission of the parasite to dogs, which represent the reservoir and potentially the main source of infection of visceral leishmaniasis due to Leishmania infantum to humans in Chad. Regarding S. clydei, it is the most common and most collected species since it represents 44.71% of Sergentomyia and is present in all five study sites. The latter is found infested by Leishmania major in Tunisia [33], it would participate perhaps next to P. duboscqi, in the transmission of cutaneous leishmaniasis.
In the present study, the number of species collected was much higher in the Sudanian zone than in the Sahelian zone and this should be influenced by the climatic and environmental conditions of temperature, humidity and rainfall. Indeed, sandfly species adapt to temperature and humidity ranges around 25–28°C and saturated humidity. These conditions are similar to those of the Sudanian zone, so that in N'Djamena, although many sandflies were captured compared to other sites, the species diversity was lower, with six species out of 13 identified. Our results are similar to those obtained in a study conducted in Mali in the same geoclimatic zones where nine sand fly species were identified in the Sahelian zone compared to 13 in the Sudanian zone [34]. Similarly, in Brazil, a study of sandfly community composition concluded that species richness, abundance and composition were significantly higher in the wet than in the dry environment [35].