Abstract
Background Lutzomyia longipalpis is the vector of Leishmania infantum in the New World, and its saliva inhibits classical and alternative human complement system pathways. This inhibition is important in protecting the insect´s midgut from damage by the complement. L. longipalpis is a promiscuous blood feeder and must be protected against its host’s complement. The objective of this study was to investigate the action of salivary complement inhibitors on the sera of different host species, such as dogs, guinea pigs, rats and chickens, at a pH of 7.4 (normal blood pH) and 8.15 (the midgut pH immediately after a blood meal). We also investigated the role of the chicken complement system in Leishmania clearance in the presence and absence of vector saliva.ResultsThe saliva was capable of inhibiting classical pathways in dogs, guinea pigs and rats at both pHs. The alternative pathway was not inhibited except in dogs at a pH of 8.15. The chicken classical pathway was inhibited only by high concentrations of saliva and it was better inhibited by the midgut contents of sand flies. Neither the saliva nor the midgut contents had any effect on the avian alternative pathway. Fowl sera killed L. infantum promastigotes, even at a low concentration (2%), and the addition of L. longipalpis saliva did not protect the parasites. The high body temperature of chickens (40°C) had no effect on Leishmania viability during our assays.ConclusionSalivary inhibitors act in a species-specific manner. It is important to determine their effects in the natural hosts of Leishmania infantum because they act on canid and rodent complements but not on chickens (which do not harbour the parasite). Moreover, we concluded that the avian complement system is the probable mechanism through which chickens eliminate Leishmania and that their high body temperature does not influence this parasite.
Highlights
American visceral leishmaniasis (AVL), caused by Leishmania infantum
Like other Leishmania species in the New World, L. infantum has a zoonotic cycle with complex epidemiology, and it parasitises different species of mammals, including humans, canids, opossums and rodents [2]
It was demonstrated that the pH in the abdominal midgut of L. longipalpis females increases from a pH of 6 to a pH of 8.15 immediately after a bloodmeal in hamsters [22]
Summary
L. chagasi) (Kinetoplastida; Trypanosomatidae), is a life-threatening disease in humans that is distributed throughout Latin America, from Mexico to Argentina, with 90% of cases occurring in Brazil [1] It is transmitted by the bite of infected female sand flies, principally Lutzomyia longipalpis (Diptera, Psychodidae). Lutzomyia longipalpis is the vector of Leishmania infantum in the New World, and its saliva inhibits classical and alternative human complement system pathways. This inhibition is important in protecting the insects midgut from damage by the complement. It is important to determine their effects in the natural hosts of Leishmania infantum because they act on canid and rodent complements but not on chickens (which do not harbour the parasite). We concluded that the avian complement system is the probable mechanism through which chickens eliminate Leishmania and that their high body temperature does not influence this parasite
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