An inhibitor of thrombin-stimulated blood platelet aggregation from the salivary glands of the hard tick Amblyomma variegatum (Acari: Ixodidae).

The tropical bont tick, Amblyomma variegatum can cause intense skin irritation and inflammation and bites that often develop into septic wounds or abscess in their host. Crude salivary gland extract (SGE) of partially engorged A. variegatum females as well as SGE protein fractions purified by three-step reverse phase HPLC procedure were tested for their anti-aggregatory effect on isolated human blood platelets stimulated with thrombin and compared with the effect of recombinant hirudin. At concentrations 10(-3) and 5 x 10(-3) microg protein/ml the following rank order of antiplatelet activity was detected: AV 16/3 (inhibitor purified from AV-III, third purification) > SGE > AV-II (fraction from first purification) > AV-III (fraction from first purification) > hirudin. The effect of all fractions tested was dose-dependent. For fraction AV 16/3, the inhibitory effect was 49 and 61% for 10(-3) and 5 x 10(-3) microg protein/ml, respectively. The results suggest that protein fractions from A. variegatum SGE possess an antithrombin effect on human blood platelets with hirudin-like activity.