Several proteins that probably help a biting gnat transmit bluetongue, a virus of cattle and sheep, have now been pinpointed by ARS scientists.

The gnat, Culicoides variipennis (KOO-lee-coy-deez vary- uh-PENN-uss), is also called a biting fly, midge or, because of its small size, a no-see-um. The gnat proteins increase blood flow to the bite area, prevent aggregation of platelets needed to close off the wound, and inhibit immune system cells that would help a victim fight off the virus. Researchers already knew about similar proteins in other biting insects and ticks. But the ARS team is the first to show that C. variipennis secretes these specialized molecules from its salivary glands. The proteins may prove to be a better tool than the virus itself for use in developing a bluetongue vaccine. That's because the many strains or serotypes of the virus can quickly develop resistance to a virus-oriented vaccine. This problem wouldn't occur with a vaccine targeted to the gnats' salivary-gland proteins. Bluetongue annually costs the U.S. livestock industry an estimated $120 million in lost trade. Countries without the disease won't accept some American livestock exports.
Arthropod-borne Animal Diseases Research Laboratory, Laramie, WY
Walter J. Tabachnick, (307) 766-3600, tabachni@uwyo.edu