Distribution and Incidence

Tularemia, in humans, is confined to the Northern Hemisphere with three main areas of epidemicity: North America, Europe, especially eastern Europe and Russia, and to a lesser extent Japan. It is not found in nature in the British Isles. Tularemia has been reported everywhere in the United States except Hawaii. In Canada, the disease is endemic in the central and western provinces, as well as the Northwest Territories, but seldom is reported from the eastern provinces. Other countries that have reported the disease include Mexico, Norway, Sweden, Belgium, France, Germany, Poland, Czechoslovakia, Austria, Yugoslavia, Turkey, and Tunisia. Sporadic cases have been reported from northern South America including Venezuela, Ecuador, and Colombia, but these have not been confirmed.

In the United States, tularemia became a reportable disease in 1927 and rose to a peak incidence in 1939 with 2,291 cases reported (17.5 per million population). Since the 1950s, the disease has undergone a dramatic decline. In 1984 in the United States only 291 cases were reported (1.2 per million). Since 1931 in Canada nearly 400 cases have been reported but with a steady decline over the years. In Russia a similar decrease has been ob served. In the mid-1940s, 100,000 cases per year were reported; yet these were reduced to a few hundred cases per year by the mid-1960s. The reasons for this worldwide decline are controversial. The reasons advanced range from ecologically induced selection against the more virulent strains of F. tularensis and reduction of the organism circulating in wild reservoirs, to an increased awareness of the disease through mass education, to a failure to detect and report cases.

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