Vector competence of Culicoides sonorensis (Diptera:Ceratopogonidae) for vesicular stomatitis virus

To determine the vector competence of Culicoides sonorensis Wirth & Jones midges for vesicular stomatitis virus (VSV) -New Jersey, insects were experimentally infected per os and sampled over time. Viral replication, as determined by in situ hybridization, was seen in epithelial, neural, and hemolymph cell types throughout the insect. Spatial and temporal distribution of virus was determined by immunohistochemical examination of sequentially sampled insects. Tissues of the alimentary canal were infected in a temporal pattern that paralleled the route of digestion/ absorption: foregut and midgut by day 1, surrounding hemolymph and Malpighian tubules by day 3, and finally the midgut/ hindgut junction, hindgut, and rectal region by day 5. The circulation of virus in the hemolymph by day 3 coincided with infection of the dermis and fat bodies, the salivary glands, eyes, cerebral and subthoracic ganglia, and the ovaries. Oviduct epithelium and ovarial sheaths were infected by day 3, followed by infection of the developing oocytes by day 5. Interestingly, neural infections were seen in the subabdominal ganglia innervating the midgut in 33% of insects by 1 d postfeeding in the absence of positive staining in the hemolymph or surrounding tissues. A retrograde axonal transport infection route for these ganglia is discussed. The disseminated, productive, noncytolytic infection in Culicoides is consistent with that of all efficient biological vector for VSV. Virus readily replicated throughout the insect, passing both midgut and salivary gland infection barriers and reaching transmission-related organs in 3 d. Establishing the competence of this insect vector for VSV provides the foundation for animal transmission studies in the future. The possibility of horizontal, transovarial, and mechanical transmission is discussed.