Volume 57, Issue 3
  • ISSN: 0002-9637
  • E-ISSN: 1476-1645



Several species of biting midges are important pests and vectors of pathogens affecting humans and other animals. Bluetongue is the most economically important arthropod-borne animal disease in the United States. is the primary North American vector of the bluetongue viruses. A reddish halo surrounding a petechial hemorrhage was noticed at the site of blood feeding in previously unexposed sheep and rabbits. Salivary gland extracts of nonblood-fed 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 obtained after blood feeding. This observation suggested that the vasodilatory activity was inoculated into the host skin at the feeding site. The vasodilatory activity was insoluble in ethanol and destroyed by trypsin or chymotrypsin, which indicated that vasodilation was due to a protein. The association of cutaneous vasodilation with a salivary protein was corroborated by reversed-phase, high-performance liquid chromatography (HPLC). Fractionation of salivary gland extracts by molecular sieving HPLC resulted in maximal vasodilatory activity that coeluted with a protein having a relative molecular weight (MWr) of 22.45 kD. The vasodilator appears to be biologically active at the nanogram level. This vasodilator likely assists during feeding by increasing blood flow from host superficial blood vessels surrounding the bite site. The identification of a salivary vasodilator in may have implications for the transmission of -borne pathogens and in the development of dermatitis resulting from the sensitization of humans and animals to salivary antigens.


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