Tularemia

Tularemia is a rare but potentially life-threatening zoonotic infection caused by the gram-negative coccobacillus Francisella tularensis. It is a CDC Category A bioterrorism agent due to its extremely low infectious dose (as few as 10 organisms), ease of aerosolization, and high mortality if untreated (up to 60% for pneumonic/typhoidal forms). [1-2] The disease is frequently initially misdiagnosed; a thorough exposure history is the single most important factor in raising clinical suspicion. [3]

1. History

• Exposure history is critical: Ask about tick bites, deer fly bites, handling rabbits/hares/rodents, skinning or butchering wild game, mowing over animal carcasses, contact with sick/dead animals, and contaminated water ingestion [2][4]
• Outdoor activities: hunting, trapping, farming, landscaping, hiking in endemic areas [5]
• Occupational exposures: laboratory workers, veterinarians, farmers [2]
• Incubation period: typically 3–5 days (range 1–14 days) [3][6]
• Symptom onset is usually abrupt: high fever (38–40°C), chills, rigors, headache, malaise, myalgias (often prominent in the low back), sore throat, coryza [2]
• Ask about skin lesion/ulcer at inoculation site, painful swollen lymph nodes, eye redness/pain, sore throat, cough, chest pain, dyspnea [7]
• Pulse-temperature dissociation noted in up to 42% of patients [2][8]
• Timing: most US cases occur in summer (tick season) or winter (hunting season) [6]

2. Alarm Features

• Pneumonic tularemia: cough, dyspnea, pleuritic chest pain, hemoptysis — mortality up to 30–60% untreated [1][5]
• Typhoidal tularemia: high fever, confusion, stupor, behavioral changes, no localizing signs — high mortality [6]
• Sepsis/bacteremia: hemodynamic instability, multiorgan dysfunction
• Meningitis: altered mental status, nuchal rigidity (rare but reported) [6]
• Rapidly progressive lymphadenopathy with suppuration
• Immunocompromised patients: unusual and severe manifestations [7]
• Delayed treatment (>2–3 weeks after onset) is associated with significantly worse outcomes and higher treatment failure rates [9]

3. Medications

Effective antimicrobials (three classes with proven survival benefit): [10-11]

• Severe disease (first-line): Gentamicin 5 mg/kg/day IV (or 1.5 mg/kg q8h) or streptomycin 15 mg/kg q12h IM for 10–14 days [4]
• Mild-moderate disease (first-line per 2025 CDC): Ciprofloxacin 500–750 mg PO BID or levofloxacin 500 mg PO daily, OR doxycycline 100 mg PO BID for 14–21 days [6][11]
• Fluoroquinolones have lower relapse rates (~5–10%) compared to tetracyclines (~10–15%) [6]
• Step-down from IV aminoglycoside to oral fluoroquinolone or doxycycline is reasonable once clinically improved [4]

Contraindicated/ineffective:

• Beta-lactams: F. tularensis is intrinsically resistant — avoid empiric beta-lactam monotherapy [4][9]
• Most macrolides and anti-TB agents are ineffective [9]
• Chloramphenicol: higher relapse rates, rarely used [4]

Special populations: [6][11]

• Pregnancy: gentamicin for severe disease; azithromycin may be considered for mild type B infections in western Europe
• Children: gentamicin preferred for severe disease; ciprofloxacin has been used safely in children ages 1–10
• Renal impairment: dose-adjust aminoglycosides

4. Diet

• No specific dietary triggers or restrictions
• Avoid consumption of undercooked wild game (especially rabbit) and untreated water from endemic areas — these are transmission routes for oropharyngeal tularemia [2]
• Maintain adequate hydration during febrile illness
• Prolonged illness may cause significant weight loss and anorexia — nutritional support may be needed [2]

5. Review of Systems

• Constitutional: fever, chills, rigors, night sweats, fatigue, weight loss, anorexia [2][7]
• Skin: ulcer or papule at inoculation site, rash, erythema nodosum [6]
• Lymphatic: painful swollen lymph nodes (location correlates with inoculation site) [12]
• Pulmonary: cough (dry or productive), dyspnea, pleuritic pain, hemoptysis, substernal tightness [2]
• GI: nausea, vomiting, diarrhea, abdominal pain, sore throat, pharyngitis [2][7]
• Ophthalmologic: eye pain, photophobia, tearing, conjunctival injection [7]
• Neurologic: headache, confusion, stupor (typhoidal form) [6]
• MSK: myalgias, arthralgias [6]

6. Collateral History and Family History

• No person-to-person transmission — household contacts are not at risk from the patient [2]
• Collateral from family/companions regarding shared outdoor exposures (hunting trips, tick-endemic areas, animal contact)
• Ask about sick or dead animals in the area (epizootics may herald human outbreaks) [2]
• Occupational history of family members (farming, veterinary work)
• No known hereditary susceptibility; immunocompromised status (HIV, transplant, chemotherapy) increases severity [6]

7. Risk Factors

• Tick exposure: Dermacentor variabilis, D. andersoni, Amblyomma americanum are primary US vectors [12-13]
• Animal contact: handling rabbits, hares, rodents, squirrels; cat bites/scratches [4][14]
• Occupational: hunters, trappers, butchers, farmers, landscapers, laboratory workers [2][5]
• Geographic: south-central US (Missouri, Arkansas, Oklahoma), Great Plains, parts of Massachusetts; all states except Hawaii [7][15]
• Seasonal: summer (arthropod-borne) and winter (hunting-related) [6]
• Age/sex: highest incidence in children 5–9 years and men >55 years [15]
• Aerosol exposure: mowing over infected animal carcasses, laboratory accidents [2][7]
• Immunocompromise: more severe and atypical presentations [7]

8. Differential Diagnosis

The differential depends on the clinical form:

• Ulceroglandular: cat scratch disease (Bartonella henselae), sporotrichosis, cutaneous anthrax, plague, staphylococcal/streptococcal lymphadenitis, Mycobacterium marinum, spider bite [4]
• Glandular/lymphadenopathy: tuberculosis, lymphoma, mononucleosis, toxoplasmosis, HIV — tularemia can produce caseating granulomas mimicking TB [16]
• Pneumonic: community-acquired pneumonia, TB, Q fever, plague, psittacosis, lung malignancy, lymphoma — pulmonary tularemia on PET/CT can mimic cancer with hypermetabolic nodules [17]
• Oropharyngeal: streptococcal pharyngitis, infectious mononucleosis, diphtheria, peritonsillar abscess
• Typhoidal: typhoid fever, brucellosis, endocarditis, malaria, rickettsial diseases
• Oculoglandular: adenoviral conjunctivitis, chlamydial conjunctivitis, Parinaud oculoglandular syndrome (cat scratch disease)

9. Past Medical History

• Prior tularemia episodes (cellular immunity is long-lasting; reinfection tends to be localized) [8]
• Immunocompromising conditions: HIV/AIDS, organ transplant, chemotherapy, chronic corticosteroid use — associated with more severe and atypical disease [6-7]
• Chronic lung disease (increases risk of severe pneumonic form)
• Renal impairment (affects aminoglycoside dosing)
• Prior tick-borne illness history
• Surgical history: prior lymph node excision or drainage

10. Physical Exam

• Vitals: high fever (38–40°C), pulse-temperature dissociation (relative bradycardia) in up to 42%; tachypnea if pneumonic [2][8]
• Skin: look for a papule or ulcer with eschar at the inoculation site — may be on extremities (tick bite), hands/arms (animal handling), or healed/inconspicuous by presentation [4][12]
• Lymph nodes: tender, enlarged regional lymphadenopathy; may be suppurative or fluctuant; location correlates with inoculation site (inguinal/femoral for lower extremity tick bites, axillary for upper extremity contact) [12]
• Oropharynx: exudative pharyngitis/tonsillitis with cervical lymphadenopathy (oropharyngeal form) [7]
• Eyes: unilateral painful conjunctivitis with preauricular/cervical lymphadenopathy (oculoglandular form) [7]
• Lungs: may be clear or have crackles, decreased breath sounds, signs of pleural effusion (pneumonic form)
• Abdomen: hepatosplenomegaly possible in systemic disease
• Neurologic: confusion, stupor in typhoidal form [6]

11. Lab Studies

• Serology (primary diagnostic method): microagglutination test for IgM/IgG — seroconversion typically occurs 2–3 weeks after symptom onset; paired acute and convalescent sera (2–3 weeks apart) are ideal; a 4-fold rise in titer or seroconversion confirms diagnosis [4][6-7]
• Culture: optimal but challenging; requires cysteine-enriched media (chocolate agar, cysteine heart agar); blood cultures often negative; MUST alert the laboratory if tularemia is suspected due to biosafety risk [4][7][18]
• PCR: useful for rapid detection from ulcer swabs, lymph node aspirates, respiratory specimens, blood; more sensitive than culture for skin/lymph node specimens [6]
• CBC: often nonspecific; may show leukocytosis or normal WBC
• CMP: mild hepatitis (elevated transaminases) is common [8]
• Inflammatory markers: elevated ESR, CRP
• Blood cultures: low yield but should be obtained in systemic/severe disease [6]

12. Imaging

• Chest X-ray: first-line for pneumonic symptoms; findings are nonspecific — infiltrates, hilar lymphadenopathy, pleural effusion [18]
• Chest CT: more sensitive; typical findings include mediastinal lymphadenopathy, pulmonary nodules, subpleural round consolidations, and pleural effusion [17][19]
• PET/CT: can show intensely hypermetabolic lesions mimicking malignancy — important pitfall [17]
• Ultrasound: useful for evaluating suppurative lymph nodes and guiding aspiration
• Imaging is unnecessary for uncomplicated ulceroglandular/glandular disease without respiratory symptoms

13. Special Tests

• Direct immunofluorescence assay (DFA): can be performed on tissue specimens [7]
• Immunohistochemical staining: useful on biopsy specimens [7]
• MALDI-TOF mass spectrometry: can identify F. tularensis from culture isolates [6]
• CT-guided biopsy: may show necrotizing granulomatous inflammation — nonspecific, can mimic TB or malignancy [16-17]
• Lymph node aspiration/biopsy: for suppurative nodes; send for culture, PCR, and histopathology
• No validated clinical scoring system specific to tularemia; diagnosis relies on clinical suspicion + exposure history + laboratory confirmation

14. ECG

• ECG is not routinely indicated for tularemia
• Cardiac involvement is very rare: anecdotal reports of pericarditis (usually with concomitant pneumonia), extremely rare myocarditis, and a single reported case of endocarditis [14][20-21]
• Consider ECG if substernal chest pain, dyspnea, or signs of myocarditis/pericarditis are present
• Monitor for QTc prolongation if using fluoroquinolones

15. Assessment

Six clinical forms based on route of inoculation: [1-2][4]

(Frequencies from Missouri surveillance data) [3]

Severity stratification: Type A strains (North America) are more virulent than type B (holarctica); subtype A1b carries the highest case fatality (~24%). [6] Overall US case fatality with treatment is approximately 2.3%. [10] Lymph node suppuration occurs in ~30% and may require surgical drainage. [6][9] Delayed diagnosis (>2–3 weeks) significantly worsens prognosis. [9]

16. Treatment Plan

Initial stabilization: IV access, fluid resuscitation, antipyretics for severe/systemic disease.

Antimicrobial therapy (per 2025 CDC recommendations and IDSA guidelines): [4][11]

• Severe disease (pneumonic, typhoidal, septic, or acutely ill):
  • Gentamicin 5 mg/kg/day IV (traditional dosing: 1.5 mg/kg q8h) or streptomycin 15 mg/kg q12h IM
  • Duration: 10–14 days
  • Step-down to oral fluoroquinolone or doxycycline once clinically improved
• Mild-moderate disease (ulceroglandular, glandular):
  • Ciprofloxacin 500–750 mg PO BID or levofloxacin 500 mg PO daily
  • OR doxycycline 100 mg PO BID
  • Duration: 14–21 days (minimum 14 days to reduce relapse risk)
• Postexposure prophylaxis: doxycycline 100 mg PO BID or ciprofloxacin 500 mg PO BID for 14 days [11][18]

Surgical intervention: drainage or excision of suppurative lymph nodes when antibiotics alone are insufficient — especially common in delayed presentations [9]

Key pearl: F. tularensis is resistant to beta-lactams. If a patient with an ulcer and lymphadenopathy fails empiric beta-lactam therapy, tularemia should be strongly considered. [4][9]

17. Disposition

• Admit for:
  • Pneumonic or typhoidal tularemia
  • Sepsis or hemodynamic instability
  • Need for IV aminoglycoside therapy
  • Significant comorbidities or immunocompromise
  • Inability to tolerate oral medications
  • Diagnostic uncertainty with concerning features
• Discharge with outpatient management for:
  • Mild ulceroglandular or glandular disease in immunocompetent patients
  • Able to tolerate oral antibiotics (fluoroquinolone or doxycycline)
  • Reliable follow-up ensured
• Observation: consider for moderate illness pending culture/serology results and clinical trajectory
• Consult infectious disease for: atypical presentations, treatment failure, immunocompromised patients, suspected bioterrorism exposure, or need for surgical management of suppurative nodes [11]
• Notify public health: tularemia is a nationally notifiable disease — report to local/state health department [15]
• Standard precautions are adequate; no person-to-person transmission [2][18]

18. Follow Up / Return Precautions

• Follow-up: within 1 week of ED discharge to assess clinical response; repeat at 2–3 weeks for convalescent serology [7]
• Relapse monitoring: treatment failures and relapses occur in 5–15% of cases depending on antibiotic class; higher with doxycycline and with delayed treatment [6][9]
• Lymph node suppuration: may develop in ~30% of patients weeks to months after initial treatment — may require surgical drainage [6][9]

Return precautions — instruct patients to return immediately for:

• Worsening or recurrent fever after initial improvement
• New or worsening shortness of breath, chest pain, or cough
• Increasing size, redness, or drainage from lymph nodes
• Confusion, altered mental status, or severe headache
• Inability to tolerate oral medications

Expected recovery: symptoms typically improve within 48–72 hours of appropriate antibiotic therapy; complete recovery may take weeks, and progressive weakness, malaise, and weight loss can persist. [2][19] Convalescence from untreated or delayed-treatment cases may last 3–12 months. [5]

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