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A study of the ecology of Buttonwillow virus during the period 1961–1968 in Kern County, California, indicated that the basic transmission cycle involves Culicoides variipennis as the vector and leporids, primarily Lepus californicus, as the vertebrate hosts. Sixty-one strains of virus were isolated from C. variipennis, but no virus was isolated from numerous pools of ticks, fleas, mosquitoes, or other biting flies. Virus also was isolated from the blood of seven L. californicus and three Sylvilagus auduboni. Hemagglutination-inhibition antibody to Buttonwillow virus was demonstrated frequently in serum from L. californicus (35.0%) and S. auduboni (12.7%), but rarely in rodents (0.7%). There was little or no serologic evidence that Buttonwillow virus infects man, domestic fowl and mammals, wild birds, marsupials, bats, carnivores, amphibians, or reptiles. Buttonwillow virus activity was detected from April through November in the San Joaquin Valley. Peak rates of infection in C. variipennis occurred during April and May, coincidental to the occurrence of peak populations of young and susceptible leporids and the initial increase of antibody prevalence in leporids. Diphasic peaks in antibody prevalence were observed for L. californicus but not for S. auduboni.
Arbovirus Field Station, P. O. Box 1564, Bakersfield, California 93302.
c/o Dr. William Hazeltine, Butte County Mosquito Abatement District, Route 2, Box 2040, Oroville Municipal Airport, Oroville, California 96965.