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Clinical Characteristics

Clinically, there are three distinctive forms of plague: bubonic, primary septicemic, and primary pneumonic. Bubonic plague is the most common and is acquired through the bite of an infected flea. The incubation period ranges from 2 to 4 days, but may be as long as 10 days. There is usually no prodromal period, although the patient may have malaise and headache for 1 or 2 days. Onset is usually abrupt, with chills and high fever to 104°F (40°C), accompanied by nausea, vomiting, oliguria, rapid pulse and respiration, and mental dullness which shortly gives way to marked anxiety or excitement. Some patients become maniacal or delirious, while others are lethargic or comatose; convulsions commonly occur in children. A bubo ( acute hemorrhagic lymphadenitis which may involve one or more nodes) is seen in 75% of patients, usually becoming apparent from the 2nd to the 5th day after the bite of the flea. It is painful, tender, hard, and about 4-5 cm in size. The inguinal nodes are most commonly involved in adults, whereas axillary and cervical nodes are the more common sites of bubo formation in children. The high fever usually lasts 2-5 days, and if the patient lives, the temperature will gradually fall to normal in about 2 weeks.

In fatal cases, secondary septicemic and pneumonic plague ensue. Marked endotoxic phenomena are usually seen, including disseminated intravascular congestion, bleeding, shock, and peripheral gangrene. Terminally there are petechiae and extensive ecchymoses throughout the body (thus the name "Black Death"). A tender hepatosplenomegaly is often present. The mortality among untreated patients with septicemic or pneumonic plague is at least 95%; death occurs rapidly within a few days, and occasionally within 24 hours, accompanied by hypothermia, cardiac or multiple organ failure, and coma. If given early and in large doses, antibiotics such as streptomycin, tetracycline and chloramphenicol are effective. If therapy is delayed, the patient may die from toxemia, despite the fact the bacilli are killed. Supportive therapy with rehydration and maintenance of blood pressure is essential.

Plague (or pestis) minor is a variation of bubonic plague in which the patients have little or no fever or toxemia and are ambulatory. There is often a bubo in the groin or less commonly the neck or axilla. These may either suppurate or gradually be resorbed. Plague bacilli may be found in the blood, sputum, or bubo, thus establishing the diagnosis, but these patients almost invariably recover. Healthy human carriers, without clinical evidence of the infection, can be identified by culturing the organisms from throat swabs. Antibiotic treatment does not hasten clearing of the carrier state.

Primary septicemic plague without bubo formation is seen in a minority of all infections. Superficial lymph nodes rarely become enlarged. There is such a high density of bacilli in the blood (up to a million or more per ml) that they are detectable on peripheral blood smear. The pathogenesis is unclear: possibly the flea injects bacilli directly into a small blood vessel. Clinically, there is sudden onset of high fever, chills, malaise, headache, anxiety, gastrointestinal upset and prostration. Meningitis and other cerebral symptoms may develop with alarming rapidity and intensity, progressing to coma. Pneumonia and hemorrhages frequently occur. The course is so rapid that, without antibiotic therapy, shock and death almost always follow in 24-72 hours. In the 1970s, septicemic plague was responsible for 11% of cases in the United States; from 1980-1984, 25% of the 71 patients with plague in New Mexico had the septicemic form, and 33% of them (6 patients) died.

In primary pneumonic plague, which is usually contracted through inhaled droplets of sputum from another patient with pneumonic plague, the onset is relatively abrupt after an initial incubation period of 24 hours or as long as 60 hours. There may be painless cough and dyspnea within the first 24 hours. The sputum is watery, thin, and blood-tinged, and contains great numbers of Y. pestis. A high fever to 104°F (40°C) develops within 24-36 hours, but there are usually few physical signs of severe illness even though most patients die in 1-2 days from acute respiratory insufficiency or endotoxic shock. These patients are a dangerous source of infection to their communities. Secondary pneumonic plague results from hematogenous dissemination in bubonic plague. The lungs are more diffusely involved than in the primary form and bacilli are more numerous in the interstitium.

Primary plague meningitis has occurred rarely in West and East Africa, South China, South America, and California. Most cases of plague with meningeal involvement closely resemble pyogenic meningitis and usually develop 9-15 days after inadequate treatment of bubonic plague. Starting with a stiff neck and headaches, convulsions and then coma develop. The cerebrospinal fluid is under pressure and the bacteria may be recovered by lumbar puncture.

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