Plague Clinical Presentation

The incubation period of plague is 3-4 days (range, hours to 10 d). Sore throat may be the only complaint of patients with plague pharyngitis.

Bubonic plague

Patients complain of fever with abrupt onset and other constitutional symptoms. These symptoms usually manifest 3-6 days after contracting the organism but may appear in the first day or be delayed for longer than a week. Clinical manifestations of plague are the same for children and adults.

Fever with chills is virtually universal. Temperatures typically range from 38.5-40ºC.

Headache, malaise, and weakness are all very common.

An area of focal lymphadenopathy (bubo) develops (see the image below).

This bubo rapidly becomes very tender and can measure up to 10 cm. Over time, fluctuance develops, and the buboes often suppurate and drain. The most common site affected is the groin, followed by the axillary and cervical lymph nodes. Intra-abdominal buboes may present as an acute abdomen.

Nausea, vomiting, diarrhea, and abdominal pain are common. These, as well as the constitutional symptoms of headache and malaise, are thought to result from the gram-negative septicemia caused by Y pestis.

Patients with plague may complain of sleep disturbance, vertigo, and loss of memory. Weakness, delirium, stupor, ataxia, and speech disorders may also occur. These manifestations are due to the effects of endotoxin on the brain. Meningitis may develop. Children younger than 15 years appear to be more susceptible to meningitis.

Septicemic plague

Constitutional symptoms are similar to bubonic plague. Absence of palpable buboes differentiates the 2 forms.

Meningitis is 4 times more common in this form of the disease than with bubonic plaque. Additionally, pneumonic plaque occurs twice as often in septicemic plaque than in the bubonic form.

Patients with septicemia are often older than 60 years. They are usually less febrile, but mortality is higher.

Bacteremia may be so great that organisms can be visualized on peripheral smears.

Pneumonic plague

Patients primarily manifest fever and respiratory symptoms, including cough, hemoptysis, and chest pain. Tachypnea and dyspnea are also common.

Thin, watery, blood-tinged sputum becomes frankly bloody and mucopurulent as the disease rapidly progresses.

Plague bacillus can be cultured from sputum, and disease transmission is thought to occur up to 2 meters from a patient who may be coughing.

Generally, patients with any form of plague are toxic in appearance. Apprehension and tachycardia are also common.

All patients are febrile with chills.

A large bubo is palpable in the groin, axilla, or neck of patients with bubonic plague. The mass is fixed, edematous, exquisitely tender, and often surrounded by an area of erythema.

Intra-abdominal buboes may be accompanied by tenderness, guarding, and other peritoneal signs. Hepatomegaly can be present.

Septicemic patients present with tachycardia, tachypnea, and hypotension. Systolic blood pressures are usually less than 100 mm Hg. Differentiation of patients with septicemic plague from patients with other types of gram-negative sepsis is often difficult due to the similarity of signs and symptoms.

Patients with pneumonic plague manifest cough productive of bloody sputum, tachypnea, and dyspnea.

Fever and meningismus accompany plague meningitis.

Patients with plague pharyngitis resemble those with any other form of bacterial pharyngitis or tonsillitis. Large anterior cervical adenopathy may be appreciated.

Bacteriology

Y pestis is a nonmotile, pleomorphic, gram-negative coccobacillus that belongs to the family Enterobacteriaceae. Bipolar staining (giving the appearance of a closed safety pin) can be observed with Giemsa, Wayson, or Wright stains (see the images below).

It grows at a wide range of temperatures (4-40ºC) but demonstrates optimal growth at room temperature.

Both an endotoxin and an exotoxin are produced, adding to the organism's pathogenicity.

Transmission

Human infection is usually acquired through the bites of infected rodent fleas. X cheopis, the Oriental rat flea, is the classic vector, but many other species of flea are also capable of transmitting plague. Typically, this form of transmission is common in crowded urban areas.

Plague can also be contracted from handling infected animals, especially rodents, lagomorphs (eg, rabbits or hares), and domestic cats, or through close contact with patients with pneumonic plague.

Person-to-person transmission is extremely rare; the last such transmission in the United States was reported in 1925. Person-to-person transmission occurs primarily through droplet exposure from a patient with the pneumonic form of the disease, although direct contact with body fluids can also be infectious.