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Selected species of wild vertebrates and hematophagous arthropods indigenous to Kern County, California, were evaluated as experimental hosts and vectors of Buttonwillow (BUT) virus. Vertebrate hosts were inoculated subcutaneously with approximately 1,000 plaque-forming units (PFU) of virus and arthropods were fed on pledgets soaked with high concentrations of virus in defibrinated blood or on viremic Sylvilagus auduboni. Two species of leporids, Lepus californicus and S. auduboni, were readily infected with BUT virus and developed high level but transient viremias. Some individual squirrels of two species, Ammospermophilus nelsoni and Citellus beecheyi, were partially susceptible to infection, whereas two other species of rodents, Dipodomys nitratoides and Peromyscus maniculatus, were refractory. Low titers of hemagglutination-inhibiting antibodies to BUT virus were demonstrated in most infected mammals and usually persisted for at least 12 weeks. Five species of wild birds were refractory to experimental infection. BUT virus multiplied in Culicoides variipennis and reached peak titers of 104.0 PFU per midge within 3 days after feeding on virus. Infection rates of BUT virus in C. variipennis were always low. A transmission cycle from viremic S. auduboni to C. variipennis to susceptible S. auduboni was completed on three occasions. Five species of mosquitoes (Aedes melanimon, Aedes nigromaculis, Anopheles free-borni, Culex tarsalis, and Culiseta inornata) and two species of ticks (Dermacentor parumapertus and Ornithodorus parkeri) were unable to serve as experimental vectors of BUT virus. High concentrations of blood from viremic S. auduboni contained a dissociable substance that partially inhibited the plaquing of virus on vero cells.
School of Public Health, University of California, Berkeley, California 94720.
Present address: Center for Disease Control, Ecological Investigations Program, P. O. Box 551, Fort Collins, Colorado 80521.