Modulation of the Host Immune System by Ectoparasitic Arthropods

Abstract

T he first things that come to mind when people think about ectoparasitic arthropods are the nuisance they cause, the irritation induced by their bites, and the disease-causing agents they transmit. Ectoparasitic insects and arachnids are often thought of as crawling or flying hypodermic needles and syringes that merely suck blood and inject disease-causing agents. However, the relationships between ectoparasitic arthropods and their hosts are far more complex. The saliva of blood-feeding arthro-pods contains a complex array of pharmacologically active molecules that help them evade host antihemostatic defenses. These compounds include inhibitors of platelet aggregation, blockers of both the intrinsic and extrinsic blood coagulation cascades, and vasodilators (Ribeiro 1995, Champagne and Valenzuela 1996). Such antihemostatic compounds have been identified in mosquitoes, sand flies, black flies, biting midges, stable flies, horseflies, tsetse flies, kissing bugs, fleas, argasid ticks, and ixodid ticks (Ribeiro 1995). Ectoparasitic arthropods also contain compounds that help them evade the effects of host grooming, a pro