Tularemia: A Brief Overview
Francisella tularensis is a nonsporulating, nonmotile, aerobic gram-negative coccobacillus that is usually transmitted to humans from infected rabbits and other small animals via ticks, fleas, or deer flies or by direct contact.
EPIDEMIOLOGY
Although tularemia was common in the United States before World War II, the incidence of this infection has declined and in recent years has remained between 0.05 and 0.15 cases per 100,000. The peak incidence is in June, September, and December.
CLINICAL COURSE
The incubation period averages 3 to 5 days, but ranges from 1 to 21 days. There are a number of possible clinical presentations, depending on the route of entry, virulence of the particular organism, and the host's immune status.
The most common presentations are ulceroglandular and typhoidal disease. The first makes up 21% to 87% of cases in the United States and is the result of skin or mucosal inoculation. Patients present with localized enlargement and tenderness of lymph nodes and one or more painful ulcerative skin lesions (Figure). The second type of presentation results from aerosol exposure and is notable for fever, headache, prostration, cough, and substernal pain, without lymphadenopathy.
Pneumonia can occur with either of these presentations but is most common with the typhoidal form.1 It can also occur as a primary disease process. Primary tularemic pneumo nia and the typhoidal form of tularemia are the most likely presentations following intentional release of F tularensis. An elevated creatine phosphokinase level, myoglobinuria, renal failure, and adult respiratory distress syndrome may complicate the course of tularemia.
DIAGNOSIS
The diagnosis of tularemia is usually made by using serologic methods (tube agglutination, microagglutination, and ELISA) at least several weeks after the onset of illness. F tularensis is fastidious in vitro, and cultivation of the causative agent is hazardous for laboratory personnel. PCR assays are not yet widely available. 2Perhaps the biggest impediment to a rapid diagnosis is the lack of clinical suspicion for tularemia in a patient with either primary pneumonia or typhoidal disease and no apparent traditional animal exposures. Streptomycin( is the drug of choice and gentamicin( is an effective alternative. 3 Approximately 35% of untreated patients die of this disease. Person-to-person spread of tularemia is extremely rare; respiratory precautions need not be observed.4