Development of Leishmania infantum/Leishmania major hybrids was studied in two sand fly species. In Phlebotomus papatasi, which supported development of L. major but not L. infantum, the hybrids produced heavy late-stage infections with high numbers of metacyclic promastigotes. In the permissive vector Lutzomyia longipalpis, all Leishmania strains included in this study developed well. Hybrids were found to express L. major lipophosphoglycan, apparently enabling them to survive in P. papatasi midgut. The genetic exchange of the hybrids thus appeared to have enhanced their transmission potential and fitness. A potentially serious consequence is the future spread of the hybrids using this peridomestic and antropophilic vector. Keywords Leishmania transmission; Parasite-vector interaction; Emerging diseasesRecently, Ravel et al. (2006) described natural genetic hybrids between Leishmania infantum and Leishmania major. These two Leishmania species are transmitted by different sand fly vectors to different mammalian reservoir hosts. Human Leishmania infantum infection is a zoonosis with dogs acting as the main reservoir. It causes potentially fatal visceral disease and in Southern Europe it has been associated with human immunodeficiency virus (HIV)-positive patients (for review see Gramiccia and Gradoni, 2005). Throughout the Mediterranean, it is transmitted by about a dozen sand fly species of the subgenus Larroussius (Killick-Kendrick, 1999). In contrast, Leishmania major circulates in arid and semi-arid areas between rodents, causing self-healing cutaneous lesions in humans (for review see Gramiccia and Gradoni, 2005). In the Middle East and Magreb area it is transmitted by Phlebotomus (Phlebotomus) papatasi (Killick-Kendrick, 1999). The discovery of natural hybrids between these very divergent Leishmania species raised many questions about the genetic exchange processes of Leishmania and possible circulation of hybrids under natural conditions (Ravel et al., 2006). This led to the current study on experimental infections of L. infantum/major hybrids in sand flies. Laboratory studies examining the development of different Leishmania strains in a range of sand fly species showed that these vectors fall into two groups. Few sand fly species are specific vectors as they display remarkable specificity for the Leishmania they transmit. For example, P. papatasi supports the development of L. major but not other parasite species tested (Killick-Kendrick et al., 1994;Pimenta et al., 1994). In contrast, most of the other sand fly species examined to date support the development of a broad range of Leishmania species and fall into the second group called permissive vectors Myskova et al., 2007). These include Phlebotomus species transmitting parasites of the Leishmania donovani complex (Pimenta et al., 1994; Myskova et al., in press) and Lutzomyia longipalpis, the New World vector of Leishmania infantum . We have chosen one member of each sand fly group to compare their susceptibility to infection by the hybrids an...
Phlebotomus papatasi (Scopoli) (Diptera: Psychodidae) is the most important vector of Leishmania major, and previous experiments revealed that Leishmania development in the sand fly midgut is significantly affected by temperature. Therefore, we maintained blood-fed P. papatasi females at 23 or 28 degrees C to understand the effect of temperature on bloodmeal digestion and developmental times of this sand fly. At the lower temperature, the metabolic processes were slower and developmental times were longer: defecation, oviposition, and egg hatch started later and took longer to complete. Also, the mortality of blood-fed females was significantly lower. The defecation of bloodmeal remains was delayed for 12-36 h at 23 degrees C compared with the group maintained at 28 degrees C. Such delay would provide more time for Leishmania to establish the midgut infection and could partially explain the increased susceptibility of P. papatasi to Leishmania major at 23 degrees C. In both experimental groups, blood-fed females laid similar numbers of eggs (mean 60 and 70, maximum 104 and 115 per female). Egg numbers were positively correlated with the amount of hematin excreted in feces of ovipositing females. In parallel experiments, autogeny was recorded in 8% of females. The autogenous egg batches were smaller (mean, 12; range, 1-39), but they all produced viable larvae.
Phlebotomus papatasi (Scopoli) (Diptera: Psychodidae) is the most important vector of Leishmania major, and previous experiments revealed that Leishmania development in the sand fly midgut is significantly affected by temperature. Therefore, we maintained blood-fed P. papatasi females at 23 or 28 degrees C to understand the effect of temperature on bloodmeal digestion and developmental times of this sand fly. At the lower temperature, the metabolic processes were slower and developmental times were longer: defecation, oviposition, and egg hatch started later and took longer to complete. Also, the mortality of blood-fed females was significantly lower. The defecation of bloodmeal remains was delayed for 12-36 h at 23 degrees C compared with the group maintained at 28 degrees C. Such delay would provide more time for Leishmania to establish the midgut infection and could partially explain the increased susceptibility of P. papatasi to Leishmania major at 23 degrees C. In both experimental groups, blood-fed females laid similar numbers of eggs (mean 60 and 70, maximum 104 and 115 per female). Egg numbers were positively correlated with the amount of hematin excreted in feces of ovipositing females. In parallel experiments, autogeny was recorded in 8% of females. The autogenous egg batches were smaller (mean, 12; range, 1-39), but they all produced viable larvae.
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