Transmission cycle analysis in a Leishmania infantum focus: Infection rates and blood meal origins in sand flies (Diptera: Psychodidae)

摘要

INTRODUCTION The two clinical forms of leishmaniasis that occur in Tunisia are caused by three Leishmania species: L. infantum, L. major, and L. killicki. The last two taxa exclusively cause cutaneous leishmaniasis (CL) and their transmission cycles have been elucidated. Indeed, the fat sand rat Psamomys obesus and Shaw’s jird Meriones shawi are the reservoir hosts with Phlebotomus (P) papatasi as the vector of L. major. The transmission cycle of CL due to L. killicki has been established recently with P. sergenti as vector and Ctenodactylus gondii as the reservoir (Jaouadi et al. 2011, 2012). However, L. infantum can cause different clinical aspects ranging from a located and spontaneous curable lesion to the general and fatal visceral leishmaniasis (VL) if untreated. This makes L. infantum the most pathogenic species in Tunisia with about 300 cases observed per year (Aoun et al. 2000). Leishmania infantum is no longer endemic only in the north of Tunisia as it has extended to the center of the country (Ben Said et al. 2012, Haoua et al. 2012, Chargui et al. 2013). Furthermore, L. infantum has a different transmission cycle that has not been completely elucidated and identified due to the presence of different taxa within L. infantum. Using the isoenzymatic method, three taxa (zymodems) were identified within L. infantum in Tunisia (MON‐1, MON‐24, and MON‐80). All of them could coexist in the same focus at different rates. With the analysis of about 500 identified strains of L. infantum (Aoun et al. 2000, 2001, 2008, Belhadj et al. 2003, Kallel et al. 2008, Haouas et al. 2012), the zymodeme MON‐1 (53.3%) was the most frequent, followed by MON‐24 (43.5%) and MON‐80 (3.2%). Only the transmission cycle of MON‐1 has been elucidated with the domestic dog as a reservoir and P. perniciosus as the vector, but those of MON‐24 and MON‐80 are still not confirmed. Indeed, neither the vector nor the reservoir has been determined for L. infantum MON‐24 and MON‐80. In rare cases, strains of MON‐24 were isolated from two dogs in Morocco (Haralambous et al. 2007) and in Algeria (Benikhlef et al. 2004). Leishmania DNA was detected in P. longicuspis (Berdjane‐Brouk et al. 2012). However, neither Leishmania parasite has been isolated in mammal reservoirs in Tunisia except for human samples. Aiming for a better understanding of the epidemiological status of L. infantum in Tunisia, we conducted an entomological study in a recently confirmed L. infantum focus (Chargui et al. 2012) by analyzing the sand fly population, detecting infected ones, and identifying blood meal origin in engorged sand flies.