Plague

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

Diagnosis

• 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