Expression variability of salivary gland genes in natural populations of the sand fly Phlebotomus papatasi (Diptera: Psychodidae)

Sand fly saliva can modulate the host hemostatic, inflammatory and immunomodulatory responses and pre-exposure to saliva or bites of uninfected sand flies protect against leishmaniases in animal models. A number of salivary proteins involved in this protection were identified. However, polymorphisms in sequence and expression of sand fly salivary gland genes can modulate disease outcome. In this study, expression polymorphisms of nine salivary gland genes were assessed in three natural populations of Phlebotomus papatasi, the main vector of Leishmania major. Sand flies were collected at different locations in Egypt (Aswan and North Sinai) and Jordan (Sweimah), during different times of the year (i.e., early and late during the sand fly season) for two years. Expression of the salivary genes SP12, SP14, SP28, SP29, SP30, SP32, SP36, SP42, and SP44 were assessed by Real-Time PCR, and potential seasonal effects were evaluated. Our results indicate that an increase in mRNA abundance towards the end of the sand fly season. This pattern of expression was detected for all the 9 genes in sand flies from Sweimah, in 7 out of 9 genes in flies from Aswan, and in 4 out of 9 genes in flies from North Sinai. The degree of variation in the expression levels detected in samples collected either early or late during a season revealed a range of expression of less than one fold to approximately 10 fold over laboratory raised unfed flies. Biotic and abiotic effects affecting the expression as well as issue related to epidemiology will be discussed.