A study of 266 authenticated cases of tularemia in California occurring from 1927–1951 showed that 81 per cent were contracted from wild rabbits. The jack rabbit appears to be more frequently involved than the cottontail, in contrast with the findings of Eastern writers. Other wild animals found infected were several species of ground squirrels and field mice, and in a few cases the brown rat. Infected arthropods found in California are chiefly ticks, although the role of rabbit fleas deserves further study, and possibly that of deerflies and horseflies.
The incidence of tularemia in the decade 1933–1942 was 16 cases a year but it has declined during the last ten years to an average of 6 cases which may in part be due to decreased reporting by clinicians who now have an effective antibiotic at hand. The seasonal occurrence with its peak in summer is associated with rabbit hunting and arthropod vector activity, but there is no correlation with the legal hunting season of cottontail rabbits. Age and sex distributions reflect the opportunity of exposure to wild rabbits. Occupation, even that of butchers, who do not handle wild rabbits plays little or no part in the epidemiology. Cases occur mainly among sportsmen and housewives who dress and cook the game.
The incidence of tularemia in California does not warrant its consideration as a major public health problem. An educational effort, particularly in the counties of greatest incidence, might help to prevent infection in hunters and their wives by teaching them how to avoid exposure when handling wild rabbits.