Abstract
A meta-analysis of the effects of vector saliva on the immune response and progression of vector-transmitted disease, specifically with regard to pathology, infection level, and host cytokine levels was conducted. Infection in the absence or presence of saliva in naïve mice was compared. In addition, infection in mice pre-exposed to uninfected vector saliva was compared to infection in unexposed mice. To control for differences in vector and pathogen species, mouse strain, and experimental design, a random effects model was used to compare the ratio of the natural log of the experimental to the control means of the studies. Saliva was demonstrated to enhance pathology, infection level, and the production of Th2 cytokines (IL-4 and IL-10) in naïve mice. This effect was observed across vector/pathogen pairings, whether natural or unnatural, and with single salivary proteins used as a proxy for whole saliva. Saliva pre-exposure was determined to result in less severe leishmaniasis pathology when compared with unexposed mice infected either in the presence or absence of sand fly saliva. The results of further analyses were not significant, but demonstrated trends toward protection and IFN-γ elevation for pre-exposed mice.
Highlights
Vector-borne diseases are a major cause of morbidity and mortality in many areas of the world
We found that saliva does enhance infection levels of vector-transmitted pathogens and leishmaniasis pathology in naıve mice and elevates Th2 cytokine levels (IL-4 and IL-10)
We determined that pre-exposure to saliva results in less severe pathology of experimental leishmaniasis in mice
Summary
Vector-borne diseases are a major cause of morbidity and mortality in many areas of the world. In addition to their cost to human health, vector-borne diseases can have a high economic cost primarily affecting impoverished nations and the people with the least resources. Like malaria and dengue fever, are infecting new populations due to lapses in vector control programs, human migration and increasing vector habitat due to climate change and other human activities [1,2,3,4,5,6,7,8]. Vaccines have been developed for some vector-borne diseases (e.g. yellow fever,) the vast majority and the most problematic still lack vaccines and viable treatment options. Results have been mixed at best, and there is some controversy as to whether saliva exacerbates disease or protects against its more severe manifestations
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