ESSENTIALS OF DIAGNOSIS
History of contact with rabbits, other rodents, and biting ticks in summer in endemic area.
Fever, headache, nausea, and prostration.
Papule progressing to ulcer at site of inoculation.
Enlarged regional lymph nodes.
Positive serologic tests or culture of ulcer, lymph node aspirate, or blood.
Tularemia is a zoonotic infection of wild rodents and rabbits caused by Francisella tularensis. Humans usually acquire the infection by contact with animal tissues (eg, trapping muskrats, skinning rabbits) or from a tick or insect bite. Hamsters and prairie dogs also may carry the organism. An outbreak of pneumonic tularemia in 2000 on Martha’s Vineyard in Massachusetts was linked to lawn-mowing and brush-cutting as risk factors for infection, underscoring the potential for probable aerosol transmission of the organism. F tularensis has been classified as a high-priority agent for potential bioterrorism use because of its virulence and relative ease of dissemination. Infection in humans often produces a local lesion and widespread organ involvement but may be entirely asymptomatic. The incubation period is typically 3–5 days.
Fever, headache, and nausea begin suddenly, and a local lesion—a papule at the site of inoculation—develops and soon ulcerates. Regional lymph nodes may become enlarged and tender and may suppurate. The local lesion may be on the skin of an extremity or in the eye. Pneumonia may develop from hematogenous spread of the organism or may be primary after inhalation of infected aerosols. Following ingestion of infected meat or water, an enteric form may be manifested by gastrointestinal symptoms, stupor, and delirium. In any type of involvement, the spleen may be enlarged and tender and there may be nonspecific rashes, myalgias, and prostration.
Culturing the organism from blood or infected tissue requires special media. For this reason and because cultures of F tularensis may be hazardous to laboratory personnel, the diagnosis is usually made serologically. A positive agglutination test (greater than 1:80) develops in the second week after infection and may persist for several years.
Tularemia must be differentiated from rickettsial and meningococcal infections, cat-scratch disease, infectious mononucleosis, and various bacterial and fungal diseases.
Hematogenous spread may produce meningitis, perisplenitis, pericarditis, pneumonia, and osteomyelitis.
Streptomycin is the drug of choice; the recommended dose is 7.5 mg/kg intramuscularly every 12 hours for 7–14 days. Gentamicin, which has good in vitro activity against F tularensis, is generally less toxic than streptomycin but some case series report lower treatment success rates. Doxycycline (200 mg/day orally) is also effective but has a higher relapse rate and should only be used for the less seriously ill. A variety of other agents ...