Prior evidence that California encephalitis (CE) virus exists in Canada was based on serologic tests of wild animals. In this study it was found that indicator rabbits, caged in the Richmond, Ontario, area where seropositive wild animals previously had been trapped, developed neutralizing antibody to this virus as early as June 10 in 1962 and June 14 in 1963, 12 and 10 days, respectively, after exposure to biting insects. By replacing seropositive with seronegative rabbits, it was possible to show that the virus continued to circulate in nature until late September at which time mosquito activity virtually came to a halt.
Confirmation of the existence of a member of the California complex in the study area was provided by five viral isolates which were neutralized by specific antiserum prepared against CE virus, strain BFS-283. The five isolations have been shown by means of the complement-fixation test to be similar to one another and closely related to, if not identical with, the snow-shoe hare strain Sn-H from Montana.
This is the first isolation of a member of the California complex in Canada.
Zoonoses Laboratory, Laboratory of Hygiene, Department of National Health and Welfare, Ottawa, Ontario, Canada.
Formerly at Rocky Mountain Laboratory, U.S. Public Health Service, Hamilton, Montana. Present address: Arbovirus Vector Laboratory, Communicable Disease Center, Atlanta, Georgia.