Tularemia
Tularemia, often called rabbit fever, is an acute infectious disease passed from animals to humans. It is caused by Francisella tularensis, a facultatively anaerobic, obligate intracellular Gram-negative coccobacillus. The organism is extremely virulent (as few as 10–50 bacteria can cause serious infection) and is maintained in nature by rodents and especially by wild and domestic rabbits. It is spread by vectors such as ticks and deer flies (Chrysops discalis), or by direct contact with the blood or meat of infected animals. The most common skin form is ulceroglandular tularemia, in which a papule turns into a necrotic, punched-out ulcer with firm, depressed edges, accompanied by painful, suppurating swelling of the regional lymph nodes.
At Haute-Derma, suspected Francisella tularensis infection is managed under strict biosafety controls, with confirmation by PCR or serology, potent antibiotics that act against intracellular bacteria, and cosmetic laser treatment to fade dark marks and scars after recovery.
Pathogenesis and Transmission
Sources of Infection and Routes of Entry
- Host-vector cycle: Francisella tularensis circulates naturally in wild rabbits, squirrels, mice and other small rodents. Deer flies (Chrysops discalis) and ticks (Dermacentor, Amblyomma) feed on infected animals and then pass the bacteria to people through their bites.
- Direct contact: the bacteria enter through tiny breaks in the skin when people skin or butcher infected rabbits or other wild game, or when they are scratched or bitten by an infected animal.
Survival Inside Macrophages and Granuloma Formation
- Escaping the phagosome: once in the dermis, F. tularensis is engulfed by macrophages. Thanks to its Francisella pathogenicity island (FPI), however, it quickly breaks down the phagosome membrane, escapes into the cytoplasm and multiplies rapidly inside the macrophage.
- Necrotizing granulomatous inflammation: the bacteria burst their host cells and travel through the lymphatics to the regional lymph nodes. There they trigger an intense cell-mediated immune response, forming granulomas with central necrosis (caseating granulomas) and pockets of pus within the nodes.
Clinical Forms Affecting the Skin
Ulceroglandular Tularemia (75–85% of Cases)
- Incubation period: 3–5 days (range 1–14 days) after a tick bite or other exposure.
- Skin lesion at the entry site: a painless red papule appears first. Within 24–48 hours it becomes a pustule, develops central necrosis and breaks down into a round ulcer with firm, depressed edges and a dusky red rim. The ulcer usually measures 1–3 cm, with a gray-black pseudomembrane or dry crust at its base.
- Severe regional lymphadenitis: the draining lymph nodes (in the armpit, groin or neck) swell rapidly, become very painful and stuck to surrounding tissue, and quite often (30–40%) fill with pus and rupture through the skin.
Glandular Tularemia
The bacteria enter through the skin but leave no obvious ulcer. Patients develop high fever and shaking chills with painful regional node swelling, as in the ulceroglandular form.
Oculoglandular Tularemia and Secondary Allergic Skin Reactions
- Oculoglandular form: bacteria splash into the eye while handling animal meat or are rubbed in with contaminated hands, causing pustular conjunctivitis and corneal ulcers with severe swelling of the nodes in front of the ear or under the jaw.
- Secondary allergic skin lesions: about 20% of patients develop erythema nodosum or erythema multiforme as an immune hypersensitivity reaction at the height of the illness.
Assessment and Diagnosis at Haute-Derma
Exposure History and Clinical Examination
- A detailed history of hiking, hunting, skinning or preparing wild rabbits, or tick or fly bites within the past 2 weeks.
- Dermoscopy of the punched-out ulcer, and Doppler ultrasound of the regional nodes to detect deep areas of necrosis and pus early.
Microbiologic Confirmation and Biosafety
- Safety warning: Francisella tularensis is a high-risk biological agent (risk group 3). It may only be cultured in a biosafety level 3 (BSL-3) laboratory to protect staff from airborne infection.
- Preferred tests: PCR to detect Francisella tularensis DNA in an ulcer swab or lymph node aspirate, and serology (IgM/IgG by IFA or MAT) showing a fourfold rise in antibody titer between the acute and convalescent phases.
Medical Treatment and Cosmetic Recovery at Haute-Derma
Antibiotics Against Intracellular Bacteria
- First-line parenteral treatment for severe or hospitalized cases:
- Gentamicin 5 mg/kg/day intravenously (or intramuscularly) in 1–2 divided doses for 7–10 days.
- Or streptomycin 1 g intramuscularly twice daily for 7–10 days.
- Oral treatment for mild cases or outpatients:
- Doxycycline 100 mg by mouth twice daily for 14–21 days (a longer course is needed to prevent relapse).
- Or ciprofloxacin 500 mg by mouth twice daily for 10–14 days.
Managing Suppurative Nodes and Restoring the Skin
- Node aspiration: when a node fills with pus and becomes tense and painful, the pus is drained by ultrasound-guided fine-needle aspiration (FNA) under strict sterile conditions. Wide incision of the node is avoided to prevent a long-lasting sinus tract.
- Repairing depressed ulcer scars:
- Once the ulcer is free of infection and granulation tissue has formed, an epidermal growth factor (EGF) serum with niacinamide and madecassoside is applied to stimulate new collagen.
- Fractional CO2 laser combined with cosmetic mesotherapy injections smooths punched-out scars and fades post-inflammatory hyperpigmentation (PIH).
