Proceedings of the Vertebrate Pest Conference

The history of plague in California is reviewed, as well as efforts to control sylvatic plague when it occurs. Recent information indicates that rodent species that suffer periodic violent epizootics, such as ground squirrels, marmots, and chipmunks, previously thought to be the most important reservoirs of plague, are not the species in which plague persists. Rather, small rodents such as Peromyscus and Microtus appear to be capable of maintaining a quiet state of infection with little or no mortality. Plague is now thought to persist in relatively small pockets where suitable climate, flea vectors, and rodent hosts occur, characteristically in cold mountainous or high plateau regions, or coastal fog belts. Permanent suppression of sciurid rodents can be justified in only a few areas, namely where there is a strong probability of enzootic plague in close proximity to human exposure. Otherwise, we should be prepared reduce squirrel numbers in appropriate areas when they become dense enough to afford an epizootic potential. In recreation areas, flea control is wholly suitable alternative. This calls for changes in the traditional practice of control of ground squirrels and other species.