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Key Features

Essentials of Diagnosis

  • Sudden onset of fever, chills, and prostration

  • Regional lymphadenitis with suppuration of nodes (bubonic form)

  • Hemorrhage into skin and mucous membranes and shock (septicemia)

  • Cough, dyspnea, cyanosis, and hemoptysis (pneumonia)

  • History of exposure to infected animals

General Considerations

  • Caused by Yersinia pestis

  • Transmitted from rodents to humans by flea bites

  • Plague bacilli have been isolated from ground squirrels, prairie dogs, and other wild rodents in many of the western and southwestern states in the United States

  • Most cases have come from New Mexico, Arizona, Colorado, and California

  • Most cases occur from June through September

  • Plague assumes several clinical forms

    • Two most common are bubonic and septicemic

    • Pneumonic plague is uncommon

Clinical Findings

Symptoms and Signs

  • Bubonic plague

    • Incubation period of 2–8 days

    • Sudden onset of high fever, chills, headache, vomiting, and marked delirium or clouding of consciousness

    • A less severe form also exists, with a less precipitous onset, but with progression over several days to severe symptoms

    • Although the flea bite is rarely seen, the regional lymph node, usually inguinal and unilateral, is painful and tender, 1–5 cm in diameter; node usually suppurates and drains spontaneously after 1 week

    • Plague bacilli produce endotoxin that causes vascular necrosis

    • Bacilli may overwhelm regional lymph nodes and enter the circulation to produce septicemia

    • Severe vascular necrosis results in widely disseminated hemorrhage in skin, mucous membranes, liver, and spleen

    • Myocarditis and circulatory collapse may result from damage by the endotoxin

    • Plague meningitis or pneumonia may occur following bacteremic spread from an infected lymph node

  • Septicemic plague

    • Plague may initially present as septicemia without evidence of lymphadenopathy

    • May present with a nonspecific febrile illness characterized by fever, myalgia, chills, and anorexia

    • May be complicated by secondary seeding of the lung causing plague pneumonia

    • Necrosis of distal body parts such as fingers, toes, and the nose tip may occur

  • Primary pneumonic plague

    • Inhalation of Y pestis bacilli causes primary plague pneumonia

    • Transmitted from human-to-human and to humans from cats with pneumonic plague

    • Incubation of 1–6 days

    • Presents with fever, cough, shortness of breath, and bloody, watery, or purulent sputum

    • Gastrointestinal symptoms are sometimes prominent

Differential Diagnosis

  • Bubonic form

    • Resembles tularemia, anthrax, cat-scratch fever, streptococcal adenitis, and cellulitis

    • Primary gastroenteritis and appendicitis may have to be distinguished

  • Septicemic form

    • Meningococcemia

    • Sepsis caused by other bacteria

    • Rickettsioses


  • Aspirate from a bubo contains bipolar-staining gram-negative bacilli

  • Pus, sputum, and blood all yield the organism

  • Rapid diagnosis can be made with fluorescent antibody detection or polymerase chain reaction (PCR) on clinical specimens

  • Confirmation is made by culture or serologic testing

  • Cultures are usually positive within 48 hours

  • Paired acute and convalescent sera may be tested for a fourfold antibody rise

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