Pathogenesis and morphology
Having penetrated through skin or mucous barriers, the pathogen is captured by cells of the mononuclear phagocyte system. Incomplete phagocytosis is established. Bacteria accumulate at the site of entry and in regional lymph nodes.
The key morphological substrate of the disease is the specific tularemia granuloma:
- A focus of necrosis is located in the center.
- In the periphery are epithelioid cells, giant cells, lymphocytes, and a large number of neutrophils.
- Unlike tuberculosis granulomas, tularemia granulomas are prone to rapid fusion, necrosis, and suppuration.
Lymphogenic dissemination leads to the formation of first- and second-order buboes, and if the lymphatic barrier fails, hematogenic generalization is possible with foci in the liver, spleen, lungs, and skeletal muscles (rhabdomyolysis).
General symptoms of the initial period
Regardless of the clinical form, tularemia begins acutely with a pronounced infectious-toxic syndrome:
- Fever: temperature rise up to 38–40 °C (remittent, intermittent, or undulating curve in protracted courses). Decreases by lysis.
- Myalgia: pain in the calf muscles and lower back is particularly pronounced.
- Facies tularaemica: typical appearance of the patient. The face (especially eyelids, lips, earlobes) acquires a bluish-purple hue, conjunctival hyperemia and scleral injection are pronounced, but the chin remains pale.
- Hepatosplenomegaly syndrome: enlargement of the liver from days 2–3, and the spleen on days 6–9.
Clinical forms of external localization
Most commonly associated with contact transmission route (via skin/mucous membranes):
- Ulceroglandular (50–70%): a primary affect forms at the portal of entry (bite, microtrauma). It sequentially passes through the stages: macula $\rightarrow$ papule $\rightarrow$ vesicle $\rightarrow$ pustule $\rightarrow$ ulcer. The ulcer has raised edges, scanty discharge, and is mildly painful, which is why it often goes unnoticed. Accompanied by regional lymphadenitis.
- Glandular (bubonic): primary affect is absent. The tularemia bubo—a conglomerate of enlarged, fused lymph nodes—comes to the forefront. Necrotization within it proceeds asynchronously. Outcome of the bubo: resolution (up to 3–4 months), sclerosis, or suppuration with rupture («creamy» pus discharge, fistulous tract formation).
- Oculoglandular (1–2%): as a rule, unilateral acute conjunctivitis, marked eyelid edema, formation of yellow-white nodules-ulcers on the ocular mucosa. Always combined with lymphadenitis (preauricular, submandibular).
- Oropharyngeal (1–4%): occurs via alimentary infection. Proceeds as unilateral tonsillitis with grayish-white fibrinous deposits and moderate pain. Specific marker: regional lymphadenitis continues to progress even after complete resolution of the tonsillitis.
Visceral and generalized forms
These forms are more severe and often require differential diagnosis with sepsis, typhoid fever, or tuberculosis:
- Pulmonary form: associated with aspiration infection. Proceeds as tracheobronchitis (without rhinitis) or severe bronchopneumonia. Foci in the lungs are prone to fusion, resemble caseous necrosis, and can form tularemia cavities. Often complicated by pleurisy. Pneumonia is characterized by a stubborn course and resistance to beta-lactams.
- Gastrointestinal (abdominal): involvement of the intestinal lymphoid apparatus (mesenteric lymphadenitis). Abdominal pain mimics the clinical presentation of an «acute abdomen». A switch from diarrhea to constipation is characteristic. Ultrasound reveals dense conglomerates of nodes in the abdominal cavity, with potential peritonitis upon their suppuration.
- Generalized form: proceeds as septicopyemia. Characterized by severe toxicosis, persistent hepatosplenomegaly, and specific rash. The exanthema has a symmetrical localization in the form of tularemic «gloves», «gaiters», «socks» and a facial «mask». The color of the eruptions evolves from pink-red to purple-copper and bluish («fading»).
Briefly: answers to topical questions
Which antibacterial drugs are used for etiotropic therapy of tularemia?
For etiotropic therapy of tularemia, antibacterial drugs from the aminoglycoside and tetracycline groups, as well as rifampicin and chloramphenicol, are used. The duration of the course should be at least two weeks.
Drugs of choice include:
- Gentamicin — intramuscularly or intravenously at a dose of 3–5 mg/kg/day.
- Amikacin — parenterally at 10 mg/kg/day.
- Streptomycin — at 7.5–10 mg/kg twice daily.
- Doxycycline — at 200 mg/day parenterally or orally.
- Rifampicin — at a dose of 900 mg/day.
- Chloramphenicol — at a dose of 50–100 mg/kg/day (particularly indicated if meningitis develops).
With which specific diseases should differential diagnosis of the abdominal form of tularemia be carried out?
Differential diagnosis of the abdominal (gastrointestinal) form of tularemia is carried out with:
- intestinal anthrax;
- typhoid and paratyphoid diseases;
- acute infectious diarrhea of other etiologies;
- acute surgical diseases of the abdominal cavity.
In the abdominal form of tularemia, involvement of mesenteric lymph nodes, severe abdominal pain, nausea, occasional vomiting, and potential diarrhea are taken into account.
The «gaiters, gloves, and socks» sign is an excellent landmark for the generalized form. The rash symmetrically affects the distal extremities, resembling worn clothing items.
Class and exam questions
What is asynchronous bubo suppuration?
A bubo is a conglomerate of fused nodes. Inside it, some lymph nodes may be in the stage of acute catarrhal inflammation, while neighboring ones have already melted, suppurated, and are ready to rupture.
Can you contract the pulmonary form through contact?
The pulmonary form develops primarily via the aspiration route (inhalation of dust from hay/grain contaminated with rodent excreta). However, it can also occur as a secondary complication of any other form during hematogenous dissemination.
What else to study on this topic
- Mechanisms of incomplete phagocytosis of the pathogen and macrophage sensitization
- Specific and non-specific prophylaxis of tularemia (live vaccine)
- Radiological signs of tularemic pneumonia and timing of their appearance
- Differential diagnosis of the abdominal form with yersiniosis and typhoid fever
- Morphological characteristics of first- and second-order buboes
Master the complete topic in the «Infectious Diseases» course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on «Clinical Presentation of Tularemia» and 3,312 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 41 video lessons on the subject
Other topics in the section "Zoonotic infections — 2024 study guide"
The entire section "Zoonotic infections — 2024 study guide"Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.