Rodent Population Control for Public Health and Safety

Rodent populations particularly those that live in close proximity to man constitute a perennial and often severe threat to man's health as reservoirs and often as direct sources of infection for a wide variety of viral, rickettsial, and bacterial disease producing agents. The following will discuss the place of rodent population reduction for the control of plague, a bacterial disease of rodents transmitted by fleas endemic in the western United States. Bubonic plague was first detected in North America in 1900, coincident with a worldwide pandemic which produced cases on every inhabited continent. Although the epidemic form of the disease is associated with rats and rat fleas, it was isolated from California ground squirrels in 1908 and subsequently traced as an infection of wild rodents and their fleas to as far east as the 100th meridian. Rat-borne epidemics occurred in both Pacific and Gulf Coast ports until the early 1920's. The epidemic phase in North America ended with the last rat-borne epidemic in Los Angeles in 1924. Nevertheless, isolated individual cases continued to occur almost all of them contracted from wild rodents, rabbits, or wild rodent fleas. From 1925 to the mid-1960's, human cases averaged somewhat less than two per year. In 1965, seven cases occurred on the Navajo Reservation in western New Mexico and northeastern Arizona, plus one case from northern California. This was the beginning of an increase in human cases with cyclic peaks at about 5-year intervals as shown in Figure 1. From 1974 through 1977 there were 62 human plague cases from the western United States, all attributable to wild rodent or rabbit sources, as many cases as occurred during the previous 25 years. Concurrent with the increase Figure 1. Confirmed human plague infections in the United States by year, 195