Tularemia

Tularemia is a zoonosis caused by Francisella tularensis, a small gram-negative bacillus. It is most commonly contracted by humans through bites of insects and through handling of infected animals, e.g., rabbits, hares, or muskrats. The clinical form infecting humans is ulceroglandular, with an ulcerative lesion on the skin and regional lymphadenitis.

Epidemiology. Although tularemia may be common in endemic areas, the variation in incidence is wide. Highest incidence in endemic areas occurs in the summer months, although the consumption of infected frozen meat will allow for an increase in winter months.

Pathogensis. Inoculation by insect or ingestion of infected meat represents the mode of transmission in humans. The inoculation site, skin or through mucosa, produces a tender ulcerative lesion accompanied by tender lymphadenopathy.

Clinical Manifestations. In patients primarily affected with head and neck disease, a primary ulcer is frequently not present. The only sign of illness may be a cervical mass, with or without general symptoms of infection. In other areas of the body, the inoculation site on skin results in an ulcerative lesion.

Diagnosis. The diagnosis of tularemia is based on paired antibody agglutination titers. Biopsy specimens of affected lymph nodes will show abscess formation with caseating necrosis. In the latter stages of the disease, the histologic picture will demonstrate granulomatous inflammation similar to mycobacterial infection or sarcoid.

Treatment. Treatment of the infection consists of tetracycline or streptomycin. Surgical drainage of abscessed lymph nodes may be necessary. The majority of patients respond favorably to treatment.

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