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Tularemia
is a febrile disease caused by Francisella
tularensis that resembles typhoid fever. Symptoms
are a primary local ulcerative lesion, regional lymphadenopathy, profound
systemic symptoms, and occasionally, atypical pneumonia. Diagnosis
is primarily epidemiologic and clinical. Treatment is with streptomycin,
gentamicin, chloramphenicol, or doxycycline.
Epidemiology
and Pathophysiology
The 4 types of tularemia are listed in Table 2: Gram-Negative Bacilli: Types of Tularemia* . The causative organism, F. tularensis, is a small, pleomorphic, nonmotile, nonsporulating, aerobic bacillus that enters the body by ingestion, inoculation, inhalation, or contamination. It can penetrate apparently unbroken skin but may actually enter through microlesions. Type A, a more virulent serotype for humans, is found in rabbits and rodents. Type B usually produces a mild ulceroglandular infection and is found in water and aquatic animals. Transmission among animals is by blood-sucking arthropods and cannibalism.
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Table 2
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Types of Tularemia*
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Type
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% of Cases
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Comment
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Ulceroglandular
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87
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Primary lesions on the hands or fingers
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Typhoidal
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8
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Systemic illness with abdominal pain and fever
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Oculoglandular
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3
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Inflammation of ipsilateral lymph nodes, probably caused by inoculation of the eye from an infected finger or hand
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Glandular
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2
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Regional lymphadenitis but no primary lesion and often cervical adenopathy, suggesting oral ingestion of bacteria
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*Tularemic pneumonia may be primary or may occur as the ulceroglandular type of infection.
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Hunters, butchers, farmers, and fur handlers are most commonly infected. In winter months, most cases result from contact (especially during skinning) with infected wild rabbits. In summer months, infection usually follows handling of other infected animals or birds or contact with infected ticks or other arthropods. Rarely, cases result from eating undercooked infected meat, drinking contaminated water, or mowing fields in endemic areas. In the Western states, ticks, deer flies, horse flies, and direct contact with animals are other sources of infection. Human-to-human transmission has not been reported. Laboratory workers are at particular risk because infection is readily acquired during normal handling of infected specimens. Tularemia is considered a possible agent of bioterrorism.
In disseminated cases, characteristic focal necrotic lesions in various stages of evolution are scattered throughout the body. They are 1 mm to 8 cm; whitish yellow; seen externally as the primary lesions on the fingers, eyes, or mouth; and commonly found in lymph nodes, spleen, liver, kidneys, and lungs. In pneumonia, necrotic foci occur in the lungs. Although severe systemic toxicity may occur, no toxins have been demonstrated.
Symptoms and Signs
Onset occurs suddenly, 1 to 10 (usually 2 to 4) days after contact, with headache, chills, nausea, vomiting, fever of 39.5° or 40° C, and severe prostration. Extreme weakness, recurring chills, and drenching sweats develop. Within 24 to 48 h, an inflamed papule appears at the infection site (finger, arm, eye, or roof of the mouth), except in glandular or typhoidal tularemia. The papule rapidly becomes pustular and ulcerates, producing a clean ulcer crater with a scanty, thin, colorless exudate. Ulcers are usually single on the extremities but multiple in the mouth or eyes. Usually, only one eye is affected. Regional lymph nodes enlarge and may suppurate and drain profusely. A typhoid-like state frequently develops by the 5th day, and the patient may develop atypical pneumonia, sometimes accompanied by delirium. Although signs of consolidation are frequently present, reduced breath sounds and occasional rales may be the only physical findings in tularemic pneumonia. A dry, nonproductive cough is associated with a retrosternal burning sensation. A nonspecific roseola-like rash may appear at any stage of the disease. Splenomegaly and perisplenitis may occur. In untreated cases, temperature remains elevated for 3 to 4 wk and resolves gradually. Mediastinitis, lung abscess, and meningitis are rare complications.
Mortality is almost nil in treated cases and about 6% in untreated cases. Death usually results from overwhelming infection, pneumonia, meningitis, or peritonitis. Relapses can occur in inadequately treated cases. One attack confers immunity.
Diagnosis
Diagnosis is suspected by a history of contact with rabbits or wild rodents or exposure to arthropod vectors; the sudden onset of symptoms; and the characteristic primary lesion. Patients should have cultures of blood and relevant clinical material (eg, sputum, lesions) and acute and convalescent antibody titers 2 wk apart. A 4-fold rise or a single titer > 1:128 is diagnostic. The serum of brucellosis patients may also cross-react to F. tularensis antigens but usually in much lower titers. Fluorescent antibody staining is used by some laboratories. Leukocytosis is common, but the WBC count may be normal with an increase only in the proportion of PMNs.
Because this organism is highly infectious, samples and culture media suspected of tularemia should be handled with extreme caution, and if possible, processed by a laboratory with a class B or C rating.
Treatment
The preferred drug is streptomycin 0.5 g IM q 12 h (if in a bioterrorism setting, 1 g q 12 h) until the temperature is normal, then 0.5 g once/day for 5 days. In children, the dose is 10 to 15 mg/kg IM q 12 h for 10 days. Gentamicin 1 to 2 mg/kg IM or IV tid is also effective. Chloramphenicol (oral form not available in US) or doxycycline 100 mg po q 12 h may be given until the temperature is normal, but relapses occasionally occur with these drugs, and they may not prevent node suppuration.
Continuous wet saline dressings are beneficial for primary skin lesions and may diminish the severity of lymphangitis and lymphadenitis. Surgical drainage of large abscesses is rarely necessary unless therapy is delayed. In ocular tularemia, applying warm saline compresses and using dark glasses give some relief. In severe cases, 2% homatropine 1 to 2 drops q 4 h may relieve symptoms. Intense headache usually responds to oral opioids (eg, oxycodone or hydrocodone with acetaminophen ).
Prevention
When entering endemic areas, tick-proof clothing and repellents should be used. A thorough search for ticks should be done after leaving. Ticks should be removed at once (see Sidebar 1: Rickettsiae and Related Organisms: Tick Bite Prevention ). When handling rabbits and rodents, especially in endemic areas, protective clothing, including rubber gloves and face masks, should be worn because organisms may be present in the animal and in tick feces on the animal's fur. Wild birds and game must be thoroughly cooked before eating. Water that may be contaminated must be disinfected before use.
Last full review/revision November 2005
Content last modified November 2005
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