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Smallpox and Dangerous Zoonotic Infections

Variola vera

For medical students2 min readUpdated 2026-10-10

Smallpox (Variola vera) is a highly contagious viral infection. Since the primary training text contains limited direct data on smallpox itself, this article includes detailed descriptions of other dangerous infections—such as anthrax, tularemia, relapsing fever, and brucellosis—based on the source material.

Important NoteThe base manual lacks extensive data on smallpox; other key infectious diseases are detailed instead.
AnthraxCaused by the spore-forming gram-positive bacterium *Bacillus anthracis*.
TularemiaCaused by the gram-negative coccobacillus *Francisella tularensis*.
Relapsing FeverCaused by the spirochete *Borrelia recurrentis*.

Anthrax

The causative agent is the gram-positive bacterium Bacillus anthracis. Its spores can survive in the environment for decades (up to 10 years in water, up to 30 years in soil).

Routes of Transmission:

Pathogenesis involves capsule formation and toxins that cause endothelial damage and necrosis. The most common form is cutaneous anthrax (95% of cases), characterized by the development of a malignant pustule (anthrax carbuncle).

Tularemia

An acute infectious disease caused by the gram-negative coccobacillus Francisella tularensis.

Sources and Routes of Infection: Rodents (mice, rats, hares) serve as the main reservoir. Human infection occurs via direct contact, arthropod bites, as well as alimentary and inhalation routes.

The disease manifests with systemic intoxication, fever, and lymph node involvement leading to the formation of primary tularemic buboes (characterized by necrosis and granulomatous reactions). Clinical forms include bubonic, generalized, and pneumonic types.

Epidemic Relapsing Fever

Caused by the spirochete Borrelia recurrentis. Lice act as vectors. Transmission does not occur via the bite itself, but when the louse is crushed and spirochetes enter the skin abrasions during scratching.

It is characterized by alternating bouts of high fever and remissions. Spirochetes multiply within the reticuloendothelial system (RES) before breaking out into the bloodstream. Their destruction releases endotoxins, triggering the acute febrile attack.

Brucellosis

The causative agents are bacteria of the genus Brucella (intracellular parasites of the RES).

Epidemiology: Livestock (cattle, small ruminants) and pigs serve as reservoirs. Infection frequently occurs alimentarily (via dairy and meat products), as well as through contact and aerosol inhalation.

It is characterized by the absence of a distinct primary affect, generalization of the infection with pathogen dissemination into RES organs, and a undulating (relapsing) clinical course.

Frequently asked questions

What morphological stages does the cutaneous rash undergo in smallpox?

The skin rash in smallpox progresses through six sequential developmental stages:

  • Macules — primary flat spots.
  • Papules — pea-sized solid elevations.
  • Vesicles — fluid-filled blisters.
  • Pustules — transformation into pus-filled lesions.
  • Crusts (Scabs) — drying phase of the lesions.
  • Scars (Pitting) — permanent marks left after crust detachment (especially pronounced on the face).
What specific intracellular inclusions are found in the epidermis during smallpox?

Specific viral inclusions are found within infected cells in smallpox:

  • Paschen bodies — elementary viral aggregates visible under light microscopy with special staining.
  • Guarnieri bodies — intracytoplasmic viral microcolonies within epithelial cells appearing as small granules.
What clinicomorphological forms of smallpox are distinguished based on severity?

Three main clinicomorphological forms are classified based on disease severity:

  • Mild forms — varioloid (rash progression arrests at the vesicle stage), smallpox without rash, and smallpox without fever.
  • Moderate forms — pustular (discrete) smallpox with typical features and typically no hemorrhages.
  • Severe forms — pustular-hemorrhagic ('black smallpox') and confluent smallpox, characterized by extreme severity and high mortality rates.
What macroscopic and microscopic features characterize the anthrax carbuncle?

The anthrax carbuncle features serous-hemorrhagic inflammation and deep necrosis.

  • Macroscopic features — formation of a black necrotic scab with a hard, 'charred' crust, surrounded by a purplish inflammatory ring and extensive gelatinous edema.
  • Microscopic features — exudate is poor in cellular elements. The zone of necrosis extends through all layers of the dermis and subcutaneous adipose tissue.
What pathomorphological changes develop in lymph nodes during the formation of a primary tularemic bubo?

Lymph nodes enlarge and mat together, undergoing distinct morphological alterations:

  • Necrosis and suppuration — primary foci of tissue alteration appear.
  • Granulomatous reaction — formation of specific tularemic granulomas prone to suppuration.
  • Cellular infiltration — central necrotic focus surrounded by neutrophils, eosinophils, and epithelioid cells, bordered peripherally by lymphocytes, plasma cells, and Langhans giant cells.
Which organs of the reticuloendothelial system are specifically affected during the generalization phase of brucellosis?

During the hematogenous phase of brucellosis, bacteremia leads to dissemination into organs of the macrophage system, specifically:

  • Lymph nodes.
  • Liver.
  • Spleen.
  • Kidneys.
  • Lungs.
  • Bone marrow.
Why is detailed smallpox information missing from the core text?

The source materials do not detail smallpox itself, focusing instead on anthrax, tularemia, relapsing fever, and brucellosis.

What is the most frequent clinical presentation of anthrax?

The cutaneous form occurs in 95% of cases and is characterized by the formation of an anthrax carbuncle.

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