Tularemia is a zoonotic infection caused by Francisella tularensis, one of the most infectious bacteria known — as few as 10 organisms inhaled or inoculated through skin can cause disease. Roughly 200 cases are reported annually in the United States (CDC 2011-2020), with hotspots in Arkansas, Missouri, Oklahoma, Kansas, and South Dakota, plus broader endemic activity across Scandinavia, central Europe, Japan, and Turkey.
Tularemia (ICD-10: A21) is an acute febrile zoonosis caused by Francisella tularensis, a small, aerobic, gram-negative coccobacillus. The bacterium is a facultative intracellular pathogen that replicates inside macrophages by escaping the phagosome through the Francisella pathogenicity island. Two clinically important subspecies exist: F. tularensis subspecies tularensis (Type A), restricted to North America and the more virulent form responsible for severe disease, and F.
The key symptoms of Tularemia are: Abrupt onset of fever above 38.5°C with chills, headache, and severe muscle aches typically beginning 3-5 days after exposure (incubation range 1-21 days)., A painful papule at a tick or deer fly bite site that enlarges and ulcerates over 2-3 days, leaving a punched-out lesion with a raised border most often on a limb or scalp., Painful, swollen, tender regional lymph nodes — most commonly in the groin, axilla, or cervical chain — that may suppurate and require drainage in 25-30% of cases if antibiotics start late., Painful unilateral conjunctivitis with yellowish nodules on the inner eyelid plus ipsilateral preauricular lymphadenopathy (Parinaud oculoglandular syndrome) in oculoglandular disease., Sore throat with severe exudative tonsillitis unresponsive to penicillin and accompanied by tender anterior cervical adenopathy in oropharyngeal disease., Non-productive cough, pleuritic chest pain, and shortness of breath in pneumonic disease, with chest imaging showing patchy infiltrates and hilar lymphadenopathy., Persistent high fever for more than 7 days, drenching sweats, profound fatigue, and a relative bradycardia (Faget sign) in typhoidal disease..
Diagnosis of tularemia begins with epidemiologic suspicion — fever plus skin ulcer, regional lymphadenopathy, pneumonia, or sepsis in a patient with relevant outdoor, occupational, or laboratory exposure. F. tularensis is fastidious and grows slowly on routine media; standard blood cultures may be negative or first read at 3-5 days, often after the organism has been transferred between bench staff who do not know they are handling a select agent. The CDC strongly recommends informing the laboratory in advance whenever tularemia is suspected so that the workup is performed under BSL-3 containment. Serology by tube agglutination or microagglutination remains the most commonly used confirmatory test, with a fourfold rise in titer between acute and convalescent samples (drawn 2-3 weeks apart) considered diagnostic; titers often do not become positive until 2 weeks into illness, so paired sampling is essential. Real-time PCR on ulcer swabs, lymph node aspirates, blood, or pleural fluid can confirm diagnosis within hours and is increasingly available in state public health laboratories and the Laboratory Response Network. Immunohistochemistry on tissue specimens is useful for retrospective diagnosis. Treatment should not be delayed waiting for confirmation when clinical suspicion is high — empirical antibiotic therapy reduces complications and mortality. All suspected and confirmed cases must be reported to public health authorities and the Laboratory Response Network within 24 hours.
With appropriate antibiotic therapy started within the first week of illness, overall mortality is under 2% across all tularemia presentations. Ulceroglandular disease, the most common form, resolves in 95% of patients without long-term sequelae though regional lymphadenopathy may persist for weeks to months. Pneumonic and typhoidal disease, untreated, carry historical mortality of 30-60%; with prompt aminoglycoside therapy, mortality falls to 5-10% in modern series. Subspecies tularensis (Type A) disease in North America carries higher mortality than subspecies holarctica disease seen in Europe and Asia. Relapse occurs in 6-12% of treated patients overall, concentrated in those receiving bacteriostatic agents (doxycycline) or shortened courses. Long-term complications are rare but include persistent lymphadenopathy requiring surgical excision, chronic skin scarring at ulcer sites, and rarely pericarditis or meningitis. Recovery from acute illness is usually complete by 4-6 weeks; full energy and exercise tolerance can take 2-3 months. Once recovered, patients have durable cell-mediated immunity to reinfection.
Suspected tularemia warrants immediate infectious disease consultation because of the diagnostic difficulty, the BSL-3 laboratory requirements, the public-health reporting obligation, and the consequences of treatment delay. Pneumonic and typhoidal disease require admission, intravenous aminoglycoside therapy, and respiratory isolation pending clarification of the exposure history.
Find specialists →Fever and constitutional symptoms typically resolve within 2-5 days of starting effective antibiotics. Skin ulcers heal over 2-4 weeks, often leaving a small scar. Lymph node enlargement resolves more slowly, sometimes persisting for 4-8 weeks even after microbiological cure. Pneumonic disease shows radiographic clearance over 4-12 weeks. Full return to baseline energy and exercise tolerance takes 2-3 months on average.
Rest during the acute febrile phase. Gradual return to activity once afebrile for 48 hours and improving on antibiotics. Strenuous exercise during pneumonic disease can worsen respiratory symptoms; defer until imaging clears and inflammation has settled, typically 4-6 weeks.
Look for board-certified infectious disease physicians with experience in zoonoses and tropical infections, hospital affiliations with Laboratory Response Network access, and the ability to coordinate with state public health departments. In bioterrorism scenarios, treatment will be coordinated by local public health authorities under CDC consultation; individual patients should follow the regimen prescribed by that response.
Medically reviewed by AIHealz Medical Editorial Board · May 13, 2026
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