Tularaemia: Expert Guide To Causes, Symptoms, And Treatment
Comprehensive guide to tularaemia: causes, clinical forms, diagnosis, treatment, and prevention strategies for this rare but serious bacterial infection.
Authoritative facts about tularaemia (also known as tularemia or rabbit fever) from DermNet New Zealand.
Tularaemia is a rare, potentially severe bacterial infection caused by the Gram-negative bacillus Francisella tularensis. This highly infectious pathogen is endemic in many parts of the Northern Hemisphere, particularly in rural areas where it circulates among wildlife such as rabbits, hares, rodents, and ticks. Humans are incidental hosts, acquiring the infection through various routes including arthropod bites, direct contact with infected animals, ingestion of contaminated water or food, or inhalation of aerosols. The disease manifests in six primary clinical forms: ulceroglandular, glandular, oculoglandular, oropharyngeal, pneumonic, and typhoidal, each determined by the portal of entry. Without prompt antibiotic treatment, tularaemia can lead to severe complications, including sepsis, pneumonia, and mortality rates up to 30% in untreated type A strains. Early recognition and intervention are critical, as most cases respond well to aminoglycosides like streptomycin or gentamicin.
What is tularaemia?
Tularaemia, often called ‘rabbit fever,’ is a zoonotic infection caused by Francisella tularensis, a small, non-motile, aerobic Gram-negative coccobacillus. Discovered in 1911 in Tulare County, California, it is classified into two main biovars: F. tularensis subsp. tularensis (type A, highly virulent, primarily North American) and subsp. holarctica (type B, less severe, widespread globally). Type A is associated with higher mortality and is linked to lagomorphs (rabbits/hares), while type B often involves aquatic environments and rodents. The bacterium survives well in moist environments, contaminated water, and animal tissues, evading phagocytosis via capsule-like structures and intracellular replication within macrophages. Human infections peak in summer due to tick activity, with outbreaks reported in hunters, farmers, and laboratory workers[10].
Who gets tularaemia?
Individuals at highest risk include those in endemic areas engaging in outdoor activities: hunters, trappers, veterinarians, farmers, landscapers, and hikers. Children, immunocompromised persons, and the elderly are more vulnerable to severe disease. Globally, the United States reports 200-300 cases annually, mostly in south-central and western states like Missouri and Arkansas. Europe sees sporadic outbreaks, particularly in Scandinavia and the Balkans, while cases in Australia and New Zealand are exceedingly rare. Laboratory accidents and bioterrorism concerns elevate risks for healthcare and research personnel, as F. tularensis is a category A select agent requiring biosafety level 3 handling[10].
What causes tularaemia?
F. tularensis is transmitted via multiple routes:
- Arthropod bites: Ticks (e.g., Dermacentor spp., dog ticks) and deer flies are primary vectors in North America.
- Direct contact: Handling infected carcasses (rabbits, muskrats) without gloves leads to percutaneous inoculation.
- Inhalation: Aerosolized bacteria from disturbed soil, hay, or lab cultures cause pneumonic form.
- Ingestion: Contaminated undercooked meat, unpasteurized milk, or water results in oropharyngeal disease.
- Rarely: Person-to-person transmission does not occur.
The incubation period ranges from 1-14 days (typically 3-5), with dose-dependent severity—fewer than 10 organisms can cause infection.
What are the clinical features of tularaemia?
Symptoms onset abruptly with high fever (39-40°C), chills, headache, myalgias, fatigue, and prostration, mimicking influenza or typhoid fever. Nonspecific signs include tachycardia, relative bradycardia, and splenomegaly. Clinical forms comprise 75-85% of cases.
Ulceroglandular tularaemia (75-80% of cases)
The most common form follows tick bites or skin contact. A tender, inflamed papule appears at the site (often lower extremities, fingers), evolving into a pustule that ulcerates with a clean base and black eschar. Regional lymphadenopathy develops rapidly—axillary, epitrochlear, or inguinal nodes enlarge, becoming tender and fluctuant (suppurative in 25-50%). Nodes may drain spontaneously, forming fistulas. Systemic symptoms dominate initially.
Glandular tularaemia (10-15%)
Similar to ulceroglandular but without skin ulceration; lymphadenopathy alone with fever.
Oculoglandular tularaemia (<1%)
From autoinoculation (touching eyes after handling infected material). Presents with unilateral conjunctivitis, photophobia, lacrimation, small yellow nodules on conjunctiva, and preauricular/cervical lymphadenopathy. Corneal ulcers are rare but vision-threatening.
Oropharyngeal tularaemia (rare)
Ingestion causes exudative pharyngitis, tonsillitis, cervical adenitis, and ulceration of tonsils or tongue. Abdominal pain, vomiting, and diarrhea may accompany.
Pneumonic tularaemia (15-25%)
Primary inhalation or secondary spread. Symptoms include dry cough, retrosternal pain, dyspnea, pleuritic chest pain, and hemoptysis. Radiographs show patchy infiltrates, hilar adenopathy, or pleural effusions. Can progress to ARDS or lung abscesses.
Typhoidal tularaemia (5-15%)
Severest systemic form without localizing signs. High fever, relative bradycardia, hypotension, and multiorgan involvement (hepatosplenomegaly, shock). Mortality high without treatment.
Complications: Lymph node suppuration, pneumonia, meningitis, osteomyelitis, pericarditis, or sepsis. Rash (maculopapular, scarlatiniform) in 10-20%.
How is tularaemia diagnosed?
Diagnosis combines epidemiology (exposure history), clinical features, and lab confirmation, as culture is hazardous.
- Culture: Blood, tissue, or aspirates on cysteine-enriched media (e.g., blood-glucose-cysteine agar). Notify lab for enhanced safety.
- PCR: Detects F. tularensis DNA in clinical specimens; rapid and specific.
- Serology: Tube agglutination or microagglutination (≥1:160 diagnostic post-acute phase). Cross-reacts with brucellosis.
- Imaging: Chest X-ray for pneumonia; lymph node ultrasound.
- Histology: Necrotizing granulomas with microabscesses.
Differential includes plague, cat-scratch disease, lymphoma, and rickettsioses.
What is the treatment for tularaemia?
Antibiotics are mainstay; consult infectious disease specialists. Preferred regimens:
| Drug | Dose | Duration | Notes |
|---|---|---|---|
| Streptomycin (preferred) | 15 mg/kg/day IM (max 2g/day) | 10 days | Drug of choice; safe in pregnancy |
| Gentamicin | 5 mg/kg/day IV/IM | 7-14 days | Alternative; monitor renal function |
| Doxycycline | 100 mg PO/IV q12h | 14-21 days | Mild cases; relapse risk |
| Ciprofloxacin | 500 mg PO q12h or 400 mg IV q12h | 14 days | Fluoroquinolone option |
Supportive care: drainage of fluctuant nodes, fluids, analgesics. Relapse in 10-20% if treatment inadequate. No vaccine available commercially.
What is the outcome for tularaemia?
With early antibiotics, mortality <2%; untreated: 5-30% depending on type/form. Recovery often complete, but lymphadenopathy may persist months. Type B milder prognosis. Survivors develop lifelong immunity.
How can tularaemia be prevented?
- Wear gloves handling animals; cook meat thoroughly.
- Tick prevention: repellents (DEET), permethrin clothing, prompt removal.
- Avoid mowing contaminated fields; use masks if dusty.
- Vaccination: Live attenuated (LVS) for high-risk lab workers (not public).
- Reportable disease; insect control in endemic areas.
Frequently Asked Questions
Is tularaemia contagious from person to person?
No, tularaemia is not transmitted directly between humans.
How soon do symptoms appear after exposure?
Incubation is 1-14 days, usually 3-5 days.
Can tularaemia be treated at home?
No, requires prescription antibiotics; seek immediate medical care.
Is there a vaccine for tularaemia?
No licensed vaccine for general use; investigational for high-risk groups.
What animals carry tularaemia?
Rabbits, hares, rodents, ticks, and flies.
References
- Tularemia – Infectious Diseases – MSD Manual Professional Edition — MSD Manuals. 2023. https://www.msdmanuals.com/professional/infectious-diseases/gram-negative-bacilli/tularemia
- Tularemia – Symptoms, Causes, Treatment | NORD — National Organization for Rare Disorders. 2023. https://rarediseases.org/rare-diseases/tularemia/
- Tularemia | Lyme Disease — Columbia University. 2023. https://www.columbia-lyme.org/tularemia
- Tularemia: Causes, Symptoms, Treatment & Prevention — Cleveland Clinic. 2024-01-15. https://my.clevelandclinic.org/health/diseases/17775-tularemia
- Tularemia – StatPearls – NCBI Bookshelf — National Center for Biotechnology Information. 2023-07-17. https://www.ncbi.nlm.nih.gov/books/NBK430905/
- Tularemia (Rabbit Fever) | Diagnosis & Disease Information — Infectious Disease Advisor. 2023. https://www.infectiousdiseaseadvisor.com/ddi/tularemia/
- About Tularemia – CDC — Centers for Disease Control and Prevention. 2024. https://www.cdc.gov/tularemia/about/index.html
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