Sandfly spit boosts parasite potential.

Sandfly spit boosts parasite potential

Scientists experimenting with the salivary glands of sandflies are finding that a little spit can go a long way when it comes to enhancing parasitic infectivity. Researchers at Harvard Medical School and the Harvard School of Public Health in Boston report that the tropical sandfly, Lutzomyia longipalpis, which transmits through its bite a parasitic disease, has a component in its saliva that boosts the virulence of the parasites it injects into its mammalian victims.

The researchers injected mice with measured doses of the parasite Leishmania major with and without sandfly saliva extracts, and compared the sizes of resulting skin ulcers. They found that injections with saliva resulted in sores that were five to 10 times larger than those induced by parasitic organisms alone, and that the saliva-enhanced lesions had as much as 5,000 times more parasites within a month after innoculation.

Moreover, the effect appears to be very specific; while other insect salivas can cause inflammation and a decrease in platelet aggregation in a bitten host, the researchers report that salivary extracts from insects that transmit other parasitic diseases had no effect on lesion size or the final concentration of Leishmania organisms.

The mechanism by which sandfly saliva exacerbates leishmaniasis is unknown, the scientists say. The active ingredient is apparently quite potent, however, with as little as one-tenth of a salivary gland, or 50 nanograms of protein, sufficient to produce significant effects.