Colonization of Phlebotomus papatasi changes the effect of pre-immunization with saliva from lack of protection towards protection against experimental challenge with Leishmania major and saliva.

Background: Sand fly saliva has been postulated as a potential vaccine or as a vaccine component within multi component vaccine against leishmaniasis. It is important to note that these studies were performed using long-term colonized Phlebotomus papatasi. The effect of sand flies colonization on the outcome of Leishmania infection is reported.

Results: While pre-immunization of mice with salivary gland homogenate (SGH) of long-term colonized (F5 and beyond) female Phlebotomus papatasi induced protection against Leishmania major co-inoculated with the same type of SGH, pre-immunization of mice with SGH of recently colonized (F2 and F3) female P. papatasi did not confer protection against L. major co-inoculated with the same type of SGH. Our data showed for the first time that a shift from lack of protection to protection occurs at the fourth generation (F4) during the colonization process of P. papatasi.

Conclusion: For the development of a sand fly saliva-based vaccine, inferences based on long-term colonized populations of sand flies should be treated with caution as colonization of P. papatasi appears to modulate the outcome of L. major infection from lack of protection to protection.