Tularemia Geographical Distribution of "Deerfly Fever" and the BitingFly, Chrysops discalis Williston

Abstract

Deerfly fever was described by Pearse (1) in 1911 as a disease entity of man in Utah where it had been recognized by physicians for several years. It is one of the many epidemiological manifestations of tularemia, an infectious bacterial disease of man and other animals, named and described by Francis (2) in 1920. While most cases of fever would be classed clinically as an ulceroglandular type of tularemia, epidemiologically, the cases are distinct in that (a) the initial lesion at the site of infection is usually on an exposed part of the body, i. e., hands, arms, face, or neck; (b) most of the cases occur in June, July, and August; (c) the disease has a rather restricted geographical distribution in contrast to tularemia in general, as shown in this study; and (d) the patient often observes being bitten by a deerfly and later recalls the incident when an initial lesion or ulcer develops at the site. The successful experimental studies by Francis and Mayne (3) on the transmission of tularemia by deerflies were undertaken because, as they state, popular belief had connected the occurrence of human cases of tularemia with the bites of Chrysops discalis. This species was abundant in areas where human cases were common and was known to bite man. Although it proved to be an efficient experimental vector, Francis and Mayne did not find natural infection nor did they observe the deerflies feeding on wild rabbits, a presumed source of infection in nature. A few cases of tularemia from deerfly bites are reported nearly every year in the West. At least one epidemic occurred among Civilian Conservation Corps workers near Locomotive Springs, north of Great Salt Lake, Utah, in 1935, as reported by Hillman and Morgan (4). Typical cases of fever appear to be confined to certain Western States and Canadian provinces in contrast to other epidemiological forms of tularemia which are widely distributed throughout the United States, and to a lesser extent in Canada. It is especially noticeable that few or no cases of deerfiy fever are reported in States of high tularemia incidence east of the Mississippi River. This case distribution suggests a study of and comparison with the