Plague

Q: What microorganism is the etiological agent (pathogen) of plague?

The etiological agent of plague is Yersinia pestis (the plague bacillus). This microorganism belongs to clinically significant species of the genus Yersinia. The bacterium is generally unstable in the environment and highly sensitive to disinfectants and boiling water. However, the pathogen tolerates low temperatures exceptionally well: in frozen corpses, it can remain viable for several months.

Pestis

For medical students2 min readUpdated 2026-10-10

Plague is an acute quarantine infection characterized by a fulminant course and extremely high mortality. In pathology, special attention is paid to forms complicated by septicemia, as well as strict biosafety protocols for handling deceased bodies to prevent epidemic spread.

Lung morphologyDense, variegated, gray-red with foci of necrosis

Disease courseDeath occurs within 1–3 days

DiagnosisBacteriology is mandatory due to the absence of specific morphology in sepsis

Mortality rateReaches 100% in severe forms

Pneumonic Plague

This form of the disease presents with pronounced septicemia and an extremely severe clinical picture. The patient exhibits high fever, severe dyspnea, and a cough productive of abundant bloody sputum that is heavily laden with pathogenic bacteria.

The disease progresses rapidly: its duration is only 2–3 days, and mortality reaches 100%.

Autopsy Findings (Pathological Anatomy):

Lungs: Become dense. On cross-section, the tissue appears variegated with a characteristic gray-red color. Multiple foci of necrosis and suppuration are visible.
Pleura: Covered with fibrinous deposits.
Respiratory tract: Serous-hemorrhagic inflammation develops in the bronchi and trachea.
Parenchymatous organs: Fatty degeneration is revealed, and reactive inflammatory changes can frequently be found in the stroma.

Primary Septic Plague

This form clinically presents as classic septicemia. Its main feature is its fulminant nature. The outcome occurs extremely rapidly, with patient death recorded just 1–1.5 days after the onset of symptoms.

Due to this ultra-rapid course, specific morphological changes in internal organs simply do not have time to develop. For this reason, post-mortem macroscopic and microscopic diagnosis is difficult.

The diagnosis of primary septic plague is established exclusively through bacteriological and bacterioscopic examination of blood and tissues. Mortality for this form is also 100%.

Autopsy Guidelines for Deceased with Quarantine Infections

Because plague is classified as a particularly dangerous quarantine infection with exceptionally high contagiousness, autopsies are governed by strict regulations. The primary objectives of the prosector are to prevent the spread of infection into the environment and to avoid self-infection.

Pathologist Personal Protective Equipment (PPE): The physician must wear a specialized anti-plague suit covering the face, body, hands, and feet. If unavailable, a strict alternative is used: two closed gowns, rubberized or plastic sleeves and apron, a cap, protective goggles, a mask made of 2–3 layers of gauze, two pairs of rubber gloves, and rubber boots (or galoshes). After the autopsy, all clothing must be destroyed, and the physician must shower and remain in quarantine until the official end of the epidemic.

Biosafety Protocol During Autopsy:

In the hospital: A specialized dissection suite is used. The sewage system must be shut off to prevent wastewater from spreading the infection. All fluids (water, blood, secretions) are collected in a dedicated container.
Organ removal: Internal organs must not be extracted from the body. All examinations are performed in situ (within open body cavities).
Body processing: After examination, the organs inside the body are covered with quicklime and treated with a disinfectant (such as lysol). The body is tightly wrapped in lysol-soaked sheets or placed in a coffin with quicklime and the lid is nailed shut.
Field conditions: The dissection table must be positioned downwind. The burial grave must be at least 3 meters deep, with quicklime and soil layered on the bottom. Staff clothing must be burned strictly indoors to prevent the dissemination of pathogens via smoke.

Frequently asked questions

What macroscopic and microscopic changes are characteristic of lymph nodes in bubonic plague?

Lymph nodes in bubonic plague exhibit serous-hemorrhagic inflammation, progressing to necrotic-hemorrhagic and purulent inflammation.

Macroscopic changes:

Nodes are sharply enlarged (up to 8–10 cm), dense, and fused together and to the skin.
Surrounded by severe edema; overlying skin is bluish-red and shiny.
On cross-section, the tissue is dark red with yellowish foci of necrosis and purulent breakdown.

Microscopic changes:

Serous inflammation rapidly transitions to serous-hemorrhagic.
Tissue necrosis develops, turning the inflammation into necrotic-hemorrhagic with superimposed suppuration.
An enormous number of rapidly multiplying bacteria are found in the tissue.

What microorganism is the etiological agent (pathogen) of plague?

The etiological agent of plague is Yersinia pestis (the plague bacillus).

This microorganism belongs to clinically significant species of the genus Yersinia. The bacterium is generally unstable in the environment and highly sensitive to disinfectants and boiling water. However, the pathogen tolerates low temperatures exceptionally well: in frozen corpses, it can remain viable for several months.

What is the character of the alveolar exudate during microscopic examination of the lungs in plague?

On microscopic examination of the lungs, the alveoli are filled with serous-hemorrhagic exudate, and sometimes with liquid blood.

Characteristic features of the exudate:

Contains a colossal number of pathogens, forming a peculiar 'microbial emulsion.'
At later stages, leukocytes with phagocytosed bacteria appear.
A specific sign of antibiotic-untreated plague pneumonia is the complete absence of fibrin in the exudate, serving as a key differentiator from lobar pneumonia.

Additionally, alveolar walls and interalveolar tissue undergo necrosis, and capillaries become thrombosed with necrotic debris and bacteria.

Why are there no typical macroscopic changes in primary septic plague?

Due to the fulminant course of the disease (death occurs within 1–1.5 days), specific morphological changes in organs and tissues do not have time to form.

What do the lungs look like at autopsy in pneumonic plague?

The lungs become dense, show a variegated gray-red pattern on cross-section, contain foci of necrosis and suppuration, and the pleura exhibits fibrinous deposits.

Are organs removed (evisceration) during autopsies of plague victims?

No, internal organs are not removed from the corpse. The autopsy and examination are conducted directly within the open thoracic and abdominal cavities (in situ) to minimize the risk of infection spread.

Go deeper

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Yellow Fever: Liver Injury and Hemorrhagic Syndrome
Distinguishing Sepsis from Other Infectious Diseases
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