Tularemia is the only disease caused by Francisella tularensis, a small, gram-negative, aerobic bacillus that is a potential agent of bioterrorism.
- Human infection occurs via interaction with biting or blood-sucking insects (especially ticks and tabanid flies in the spring and summer), wild or domestic animals (e.g., wild rabbits, squirrels), or the environment.
- - The organism gains entry into the skin or mucous membranes through bites or inapparent abrasions or is acquired via inhalation or ingestion.
- - As few as 10 organisms can result in infection when injected into the skin or inhaled; >108 organisms are required to produce infection via the oral route.
- More than half of U.S. cases occur in Arkansas, Oklahoma, and Missouri.
After an incubation period of 2-10 days, tularemia generally starts with an acute onset of fever, chills, headache, and myalgias. The ulceroglandular/glandular forms of tularemia affect 75-85% of pts, but several other syndromes involving systemic manifestations can occur.
- Ulceroglandular/glandular tularemia: The hallmark of ulceroglandular tularemia is an indurated, erythematous, nonhealing ulcer lasting 1-3 weeks that begins as a pruritic or tender lesion, ulcerates, has sharply demarcated edges and a yellow exudate, and develops a black base.
- - Inguinal/femoral lymphadenopathy is most common in adults; nodes can become fluctuant and drain spontaneously.
- - In glandular tularemia (5-10% of cases), no primary skin lesion is apparent.
- Oculoglandular tularemia: In 1% of pts, infection of the conjunctiva—usually by contact with contaminated fingers—results in purulent conjunctivitis with regional lymphadenopathy and debilitating pain. Painful preauricular lymphadenopathy distinguishes tularemia from other diseases.
- Oropharyngeal and GI tularemia: Acquired through oral inoculation (via contaminated foods or fingers), the infection can present as pharyngitis and cervical adenopathy, intestinal ulcerations, mesenteric lymphadenopathy, diarrhea, nausea, vomiting, and abdominal pain.
- Pulmonary tularemia: Infection is acquired via inhalation or via hematogenous spread from ulceroglandular or typhoidal tularemia. Pts present with signs and symptoms similar to those of pneumonia of other etiologies (e.g., nonproductive cough, dyspnea, pleuritic chest pain, CXR with bilateral patchy or lobar infiltrates or cavitary lesions).
- Typhoidal tularemia: Due to pharyngeal or GI inoculation or to bacteremic disease, typhoidal tularemia consists of fever and signs of sepsis, generally without skin lesions or lymphadenopathy. This form is the result of a large inoculum or a preexisting compromising condition.
The diagnosis of tularemia is most frequently confirmed by serology, although up to 30% of pts infected for 3 weeks have negative results in serologic tests.
- Cultures are positive in only 10% of cases; organisms in culture pose a significant risk to laboratory personnel.
- PCR has been used to detect F. tularensis DNA in clinical specimens, mainly for ulceroglandular disease.
Treatment: Tularemia
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