Tularemia, also known as “rabbit fever,” is a rare but serious zoonotic disease caused by the bacterium Francisella tularensis. It affects both animals and humans and is primarily transmitted through contact with infected animals or vectors such as ticks and deer flies. Due to its potential severity and transmission routes, tularemia remains a critical concern in public health, especially in endemic regions.
Understanding the Pathogen: Francisella tularensis
Francisella tularensis is a highly infectious, gram-negative coccobacillus. It is categorized as a Tier 1 Select Agent due to its potential use in bioterrorism. The bacterium has two main subspecies that cause disease in humans:
- Type A (subsp. tularensis): More virulent and commonly found in North America.
- Type B (subsp. holarctica): Less severe, prevalent in Europe and Asia.
This pathogen can survive in harsh environmental conditions and infect hosts via multiple pathways, contributing to the disease’s complexity and risk.
Routes of Transmission
Tularemia can spread through several mechanisms:
- Vector-borne transmission: Bites from infected ticks (especially Dermacentor and Amblyomma spp.) and deer flies.
- Direct contact: Handling infected animal tissues, particularly rabbits, hares, and rodents.
- Inhalation: Breathing in contaminated aerosols, often during farming or landscaping.
- Ingestion: Consuming contaminated food or water.
Clinical Forms and Symptoms
Tularemia presents in multiple forms, each associated with specific transmission routes and clinical features. The incubation period ranges from 3 to 5 days but may extend up to 14 days.
1. Ulceroglandular Tularemia
- Most common form
- Entry through skin or tick bite
- Symptoms: Skin ulcer at infection site, swollen lymph nodes, fever, chills, fatigue
2. Glandular Tularemia
- Similar to ulceroglandular but without ulcer
- Presents with regional lymphadenopathy
3. Oculoglandular Tularemia
- Entry via eye (e.g., touching eyes with contaminated hands)
- Symptoms: Conjunctivitis, photophobia, swollen lymph nodes near the ear
4. Oropharyngeal Tularemia
- Caused by ingestion of contaminated food or water
- Symptoms: Sore throat, mouth ulcers, tonsillitis, abdominal pain, diarrhea
5. Pneumonic Tularemia
- Results from inhalation of bacteria
- Symptoms: Cough, chest pain, difficulty breathing, high fever
- Most serious form, often requiring hospitalization
6. Typhoidal Tularemia
- Rare, systemic form with no localized symptoms
- Characterized by sepsis, high fever, malaise, and multi-organ involvement
Diagnostic Procedures
Timely diagnosis of tularemia is critical due to its rapid progression and potential severity.
1. Clinical Evaluation
- History of exposure (animal handling, tick bites, endemic area visit)
- Physical examination of ulcers, lymph nodes, respiratory signs
2. Laboratory Testing
- Serological tests: Detect antibodies (agglutination or ELISA)
- PCR testing: Detect F. tularensis DNA from tissue, sputum, or blood
- Culture: Requires biosafety level 3 facilities; confirms diagnosis but risky due to infectivity
3. Imaging
- Chest X-rays or CT scans in suspected pneumonic tularemia cases
Treatment Options
Prompt antibiotic therapy is essential. Without treatment, tularemia can be fatal in some forms, particularly pneumonic and typhoidal.
First-Line Antibiotics
- Streptomycin: Gold standard, effective for severe cases
- Gentamicin: Alternative aminoglycoside with similar efficacy
Alternative Treatments
- Doxycycline or Ciprofloxacin: Suitable for mild to moderate infections
- Duration: 10–14 days for aminoglycosides, 14–21 days for doxycycline or ciprofloxacin
Supportive Care
- Hydration
- Pain and fever management
- Hospitalization for severe or systemic cases
Prognosis and Complications
With early treatment, the prognosis is excellent. However, delayed or inadequate therapy may lead to:
- Persistent lymphadenopathy
- Pneumonia
- Septicemia
- Meningitis (rare)
Mortality rates are low (<2%) with appropriate care but can exceed 30% in untreated pneumonic cases.
Prevention Strategies
Preventive measures are vital, especially in endemic regions or among at-risk populations such as hunters, farmers, and veterinarians.
1. Personal Protective Measures
- Use insect repellent with DEET during outdoor activities
- Wear gloves when handling animals
- Avoid drinking untreated surface water
2. Environmental Management
- Control rodent populations
- Cook wild game meat thoroughly
- Promptly remove attached ticks using fine-tipped tweezers
3. Vaccination
- Currently, no licensed vaccine is publicly available
- Investigational Live Vaccine Strain (LVS) used in select lab workers under research protocols
Epidemiology and Global Impact
Though rare, tularemia occurs worldwide, predominantly in the Northern Hemisphere.
- United States: Mostly reported in central and south-central states
- Europe: Cases in Sweden, Finland, and the Balkans
- Asia: Endemic in parts of Russia, Japan, and China
Notable Outbreaks
- Martha’s Vineyard, USA: Linked to lawn mowing activities
- Kosovo (1999–2000): Waterborne outbreak affecting thousands
Tularemia as a Bioterrorism Threat
Due to its high infectivity, low infectious dose (10–50 organisms), and aerosol transmission capability, F. tularensis is considered a high-priority bioterrorism agent.
- Category A Pathogen (CDC classification)
- Past weaponization in the former Soviet Union and other nations
- Continued research for vaccine development and countermeasures
Tularemia, though rare, is a potentially serious disease with diverse clinical manifestations and transmission pathways. Accurate diagnosis, timely antibiotic treatment, and preventive awareness are essential in reducing its public health impact. As a zoonotic disease with bioterrorism implications, tularemia demands continued surveillance, education, and research to safeguard both human and environmental health.
FAQs
What causes tularemia?
Tularemia is caused by the bacterium Francisella tularensis, transmitted through ticks, deer flies, animal contact, ingestion, or inhalation.
Is tularemia contagious?
No, it is not spread from person to person. Transmission occurs via vectors, animal exposure, or environmental sources.
How is tularemia diagnosed?
Through clinical history, serological tests, PCR, and in some cases, culture of clinical specimens.
Can tularemia be cured?
Yes, tularemia is treatable with antibiotics like streptomycin, gentamicin, doxycycline, or ciprofloxacin.
Who is most at risk of tularemia?
Hunters, farmers, veterinarians, and individuals exposed to tick-prone or wildlife-inhabited environments are most at risk.
