IDENTIFICATION OF A SALIVARY VASODILATOR IN THE PRIMARY NORTH-AMERICAN VECTOR OF BLUETONGUE VIRUSES, CULICOIDES-VARIIPENNIS

Several species of Culicoides biting midges are important pests and ve ctors of pathogens affecting humans and other animals. Bluetongue is t he most economically important arthropod-borne animal disease in the U nited States. Culicoides variipennis is the primary North American vec tor of the bluetongue viruses. A reddish halo surrounding a petechial hemorrhage was noticed at the site of C. variipennis blood feeding in previously unexposed sheep and rabbits. Salivary gland extracts of non blood-fed C. variipennis injected intradermally into sheep and rabbits induced cutaneous vasodilation in the form of erythema. A local, dose -dependent erythema, without edema or pruritus, was noted 30 min after injection. Erythema was inapparent with salivary gland extracts obtai ned after blood feeding. This observation suggested that the vasodilat ory activity was inoculated into the host skin at the feeding site. Th e vasodilatory activity was insoluble in ethanol and destroyed by tryp sin or chymotrypsin, which indicated that vasodilation was due to a pr otein. The association of cutaneous vasodilation with a salivary prote in was corroborated by reversed-phase, high-performance liquid chromat ography (HPLC). Fractionation of salivary gland extracts by molecular sieving HPLC resulted in maximal vasodilatory activity that coeluted w ith a protein having a relative molecular weight (MWr) of 22.45 kD. Th e C. variipennis vasodilator appears to be biologically active at the nanogram level. This vasodilator likely assists C. variipennis during feeding by increasing blood how from host superficial blood vessels su rrounding the bite site. The identification of a salivary vasodilator in C. variipennis may have implications for the transmission of Culico ides-borne pathogens and in the development of dermatitis resulting fr om the sensitization of humans and animals to Culicoides salivary anti gens.