Biting Deer Flies and Disease Transmission

Biting Deer Flies and Disease Transmission

Biting deer flies, as painful and obnoxious as they can be, can also transmit the disease tularemia. Tularemia characteristically presents as an acute febrile illness. Various clinical manifestations can occur depending on the route of infection and host response, including an ulcer at the site of cutaneous or mucous membrane inoculation (Figure 1), pharyngitis, ocular lesions, regional lymphadenopathy, and pneumonia. A diagnosis of tularemia can be laboratory-confirmed by culture of F. tularensis from clinical specimens or by a fourfold titer change of serum antibodies against F. tularensis. Presumptive diagnosis can be made by detecting F. tularensis antigens with fluorescent assays or by a single elevated antibody level (1). For purposes of national surveillance, confirmed and probable tularemia cases are defined as clinically compatible illness with confirmatory or presumptive laboratory evidence of F. tularensis infection, respectively. Before September 1996, because of ambiguity in the case definition, some cases of tularemia might have been considered confirmed by fluorescent assay alone. Case status is determined at the state level. For the purposes of this report, any case reported to CDC was assumed to have laboratory evidence of infection. Similar results were obtained when the analysis was limited to cases with documented confirmed or probable status.

During 1990--2000, a total of 1,368 cases of tularemia were reported to CDC from 44 states, averaging 124 cases (range: 86--193) per year; 807 cases (59%) were reported as confirmed and 85 cases (6%) were reported as probable; the status of 476 cases is unknown. Most (91%) unclassified cases were reported during 1990--1992; all cases during 1990--1991 and 54% of cases from 1992 were not classified. The number of cases reported annually did not decrease substantially during the lapse in status as a notifiable disease during 1995--1999, but an increase in reporting occurred during 2000, when notifiable status was restored. Four states accounted for 56% of all reported tularemia cases: Arkansas (315 cases [23%]), Missouri (265 cases [19%]), South Dakota (96 cases [7%]), and Oklahoma (90 cases [7%]).

In the United States, most persons with tularemia acquire the infection from arthropod bites, particularly tick bites, or from contact with infected mammals, particularly rabbits. Historically, most cases of tularemia occurred in summer, related to arthropod bites, and in winter, related to hunters coming into contact with infected rabbit carcasses. In recent years, a seasonal increase in incidence has occurred only in the late spring and summer months, when arthropod bites are most common. Outbreaks of tularemia in the United States have been associated with muskrat handling (3), tick bites (4,5), deerfly bites (6), and lawn mowing or cutting brush (7). Sporadic cases in the United States have been associated with contaminated drinking water (8) and various laboratory exposures (9). Outbreaks of pneumonic tularemia, particularly in low-incidence areas, should prompt consideration of bioterrorism (10).

The high incidence of tularemia among males and among children aged .