A vaccine containing components of sand fly saliva may one day offer people protection against a devastating tropical illness, according to new research. In a report published today in the Journal of Experimental Medicine, scientists describe how their vaccine prevents leishmaniasis in mice.

Leishmaniasis, which comprises a group of related diseases caused by the parasite Leishmania, is transmitted through the bite of a sand fly. Earlier research had shown that lab animals immunized with sand fly saliva commonly resist infection when later bitten by Leishmania-carrying flies. With that in mind, Jos Ribeiro of the National Institute of Allergy and Infectious Disease and colleagues decided to try developing a vaccine against leishmaniasis. Specifically, the team worked with saliva from the sand fly that carries a skin-lesion-causing variant of the parasite. Analyses of the saliva revealed that one of its protein components, known as SP15, appeared to elicit a natural immune response in mice. Subsequent identification of the SP15 gene enabled the researchers to construct a DNA vaccine.

The team's unconventional vaccine worked. Mice that received it fared much better than mice that didn't when challenged with an injection containing parasites mixed with saliva. Indeed, whereas immunized mice exhibited only small lesions and cleared the infection within six weeks, unvaccinated mice suffered large ulcers and failed to get rid of the parasites.

Next Ribeiro plans to test the vaccine in dogs and monkeys, and work on developing vaccines against the other leishmaniasis variants. It won't be easy. "Different sand fly species, each with its unique collection of salivary proteins, transmit different Leishmania species," he notes. "If anti-saliva vaccines are to work in people, they will have to be specifically engineered for the problem insects of each region."

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