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Clinical Features
Plague normally appears in three forms in man:
- Bubonic
- Septicemic
- Pneumonic
Bubonic plague begins after an incubation period of 2-10 days, with acute and very rapid onset of nonspecific symptoms, including high fever, malaise, headache, muscle aches, and sometimes nausea and vomiting. Up to half of patients will have abdominal pain. Simultaneous with or shortly after the onset of these nonspecific symptoms, the bubo develops - a swollen, very painful, infected lymph node. Buboes are normally seen in the femoral or inguinal lymph nodes as the legs are the most commonly flea-bitten part of the adult human body. The liver and spleen are often tender and palpable.
One quarter of patients will have various types of skin lesions: a pustule, vesicle, scabs or sores (containing leukocytes and bacteria) in the lymphatic drainage of the bubo, and presumably representing the site of the inoculating flea bite. Secondary septicemia is common, as greater than 80% of blood cultures are positive for the organism in patients with bubonic plague. However, only about a quarter of bubonic plague patients progress to clinical septicemia. In those who do progress to secondary septicemia, as well as those presenting septicemic but without lymph infection (primary septicemia), the symptoms are similar to other bacterial septicemia: high fever, chills, malaise, hypotension, nausea, vomiting, and diarrhea.
Plague septicemia can also produce thromboses in the acral vessels, with necrosis and gangrene. Black necrotic appendages and more proximal lesions are often present. Organisms can spread to the central nervous system, lungs, and elsewhere. Plague meningitis occurs in about 6% of septicemic and pneumonic cases. Pneumonic plague is an infection of the lungs due to either inhalation of the organisms (primary pneumonic plague), or spread to the lungs from septicemia (secondary pneumonic plague).
After an incubation period varying from 1 to 6 days for primary pneumonic plague (usually 2-4 days, and presumably dose-dependent), onset is acute and often very rapid. The first signs of illness include high fever, chills, headache, malaise, and muscle aches, followed within 24 hours by a cough with blood. Although bloody sputum is characteristic, it can sometimes be watery or, less commonly, purulent. Gastrointestinal symptoms, including nausea, vomiting, diarrhea, and abdominal pain, may be present.
Chest X-ray findings are variable, but most commonly reveal bilateral infiltrates, which may be patchy or consolidated. The pneumonia progresses rapidly, resulting in shortness of breath, raspy breathing, and cyanosis. The disease terminates with respiratory failure, and circulatory collapse.
In man, the mortality of untreated bubonic plague is approximately 60% (reduced to <5% with prompt effective therapy), whereas in untreated pneumonic plague the mortality rate is nearly 100%, and survival is unlikely if treatment is delayed beyond 18 hours of infection.
Among pneumonic plague patients in the U.S. in the past 50 years, 4 of the 7 (57%) died. Data from the Madagascar epidemic, which began in 1989, corroborate that figure; the mortality associated with respiratory involvement was 57%, while that for bubonic plague was 15%.
Diagnosis
Diagnosis is based primarily on clinical suspicion. The sudden appearance of large numbers of previously healthy patients with severe, rapidly progressive pneumonia with bloody cough strongly suggests plague. A presumptive diagnosis can be made microscopically by identification of the bacteria from lymph node, sputum, blood, or cerebrospinal fluid samples.
Medical Management
Use Standard Precautions for bubonic plague patients. Suspected pneumonic plague cases require strict isolation with Droplet Precautions for at least 48 hours of antibiotic therapy, or until sputum cultures are negative in confirmed cases. If competent vectors (fleas) and reservoirs (rodents) are present, measures must be taken to prevent local disease cycles. These might include, but are not limited to, use of flea insecticides, rodent control measures (after or during flea control), and flea barriers for patient care areas.
Antibiotics
Streptomycin, 30 mg/kg/day IM in two divided dosesGentamicin, 5mg/kg IM or IV once daily, or 2mg/kg loading dose followed by 1.75 mg/kg IM or IV every 8 hoursDoxycycline, 200 mg initially, followed by 100 mg every 12 hours.- Duration of therapy is 10 to 14 days.
While the patient is typically without fever after 3 days, the extra week of therapy prevents relapses. Results obtained from laboratory animal, but not human, experience, indicate that quinolone antibiotics, such as ciprofloxacin and ofloxacin, may also be effective.
The recommended dosage of
Preventative Measures
No vaccine is currently available for prevention of plague. A licensed, killed whole-cell vaccine was available in the U.S. from 1946 until November 1998. It offered protection against bubonic plague, but was not effective against aerosolized Y. pestis.
Contact Protection
Face-to-face contacts (within 2 meters) of patients with pneumonic plague (or persons possibly exposed to a plague aerosol in a plague bioterrorism attack) should be given antibiotic prevention for seven days or the duration of risk of exposure plus seven days. If fever or cough occurs in these individuals, treatment with antibiotics should be started. Because of oral administration and relative lack of toxicity, the choice of antibiotic for prevention is doxycycline 100 mg orally twice daily.
Contacts of bubonic plague patients need only be observed for symptoms for a week. If symptoms occur, start treatment antibiotics.