Analysis of enhancing effect of sand fly saliva on Leishmania infection in mice.

Salivary gland lysates of the sand fly Lutzomyia longipalpis markedly enhance the course of infection with Leishmania major in mice. Here we examine various parameters of this phenomenon. The exacerbative effect of L. longipalpis salivary gland lysates occurred in five different mouse strains; however, the character of the effect varied from one strain to another. Consistent exacerbation of infection was achieved with as little as 1/10 of a gland. The exacerbative effect applied to more than one Leishmania species and to more than one species of sand fly, since salivary gland lysates of L. longipalpis enhanced infection with L. mexicana amazonensis and salivary gland lysates of Phlebotomus papatasi enhanced infection with L. major. A synthetic rat calcitonin gene-related peptide was also found to exacerbate infection with L. major but was found to be approximately 100-fold less potent than saliva in mediating this effect. In addition, lesions induced at skin sites at which L. longipalpis had probed for a blood meal exhibited an exacerbated course of infection similar to that seen when parasites were injected with sand fly salivary gland lysates.