Sandfly maxadilan exacerbates infection with Leishmania major and vaccinating against it protects against L. major infection.

Bloodfeeding arthropods transmit many of the world's most serious infectious diseases. Leishmania are transmitted to their mammalian hosts when an infected sandfly probes in the skin for a bloodmeal and injects the parasite mixed with its saliva. Arthropod saliva contains molecules that affect blood flow and modulate the immune response of the host. Indeed, sandfly saliva markedly enhances the infectivity of L. major for its host. If the salivary molecule(s) responsible for this phenomenon was identified, it might be possible to vaccinate the host against this molecule and thereby protect the host against infection with Leishmania. Such an approach represents a novel means of controlling arthropod-borne disease transmission. Here, we report that a single molecule, maxadilan, in sandfly saliva can exacerbate infection with L. major to the same degree as whole saliva, and that vaccinating against maxadilan protects mice against infection with L. major.