Anticoagulant activity in salivary gland extracts of black flies (Diptera: Simuliidae)

Anticoagulant activity was determined in salivary gland extracts from four species of black flies, i.e., Simulium vittatum Zetterstedt, Simulium argus Williston, Simulium metallicum Bellardi, and Simulium ochraceum Walker. Inhibition of coagulation factor Xa occurred among all four, whereas thrombin inhibition was detected in S. argus and S. vittatum only. Both bovine and human alpha-thrombins were inhibited with the highest activity occurring with S. argus salivary gland extracts. Factor Xa inhibition was highest in S. ochraceum, an anthropophilic species and vector of Onchocerca volvulus, and lowest in S. vittatum, a primiparous autogenous species that is also zoophilic. Total soluble salivary gland extract protein also varied among the four species with the highest concentration measured in S. ochraceum and the lowest in S. vittatum. A positive correlation was observed between the amount of soluble protein and percentage of inhibition of factor Xa for the four species.