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Plague is
caused by Yersinia pestis.
Symptoms are either severe pneumonia or massive lymphadenopathy
with high fever, often progressing to septicemia. Diagnosis is epidemiologic
and clinical, confirmed by culture and serology. Treatment is with
a fluoroquinolone or doxycycline.
Yersinia (formerly Pasteurella) pestis is a short bacillus that often shows bipolar staining (especially with Giemsa stain) and may resemble a safety pin.
Plague occurs primarily in wild rodents (eg, rats, mice, squirrels, prairie dogs) and is transmitted from rodent to human by the bite of an infected flea vector. Human-to-human transmission occurs by inhaling droplet nuclei from patients with pulmonary infection (primary pneumonic plague), which is highly contagious. In endemic areas in the US, several cases may have been caused by household pets, especially cats. Transmission from cats can be by bite, or if the cat has pneumonic plague, by inhalation of infected droplets.
Massive human epidemics have occurred (eg, the Black Death of the Middle Ages). More recently, plague has occurred sporadically or in limited outbreaks. In the US, > 90% of human plague occurs in the Southwest, especially New Mexico, Arizona, California, and Colorado. Yersinia is considered a possible agent of bioterrorism.
Symptoms and Signs
In bubonic plague, the most common form, the incubation period is usually 2 to 5 days but varies from a few hours to 12 days. Onset of fever of 39.5 to 41° C is abrupt, often with chills. The pulse may be rapid and thready; hypotension may occur. Enlarged lymph nodes (buboes) appear with or shortly before the fever. The femoral or inguinal lymph nodes are most commonly involved, followed by axillary, cervical, or multiple nodes. Typically, the nodes are extremely tender and firm, surrounded by considerable edema. They may suppurate in the 2nd wk. The overlying skin is smooth and reddened but often not warm. A primary cutaneous lesion, varying from a small vesicle with slight local lymphangitis to an eschar, occasionally appears at the bite. The patient may be restless, delirious, confused, and uncoordinated. The liver and spleen may be enlarged.
Primary pneumonic plague has a 2- to 3-day incubation period, followed by abrupt onset of high fever, chills, tachycardia, and headache, often severe. Cough, not prominent initially, develops within 24 h. Sputum is mucoid at first, rapidly develops blood specks, and then becomes uniformly pink or bright red (resembling raspberry syrup) and foamy. Tachypnea and dyspnea are present, but pleurisy is not. Signs of consolidation are rare, and rales may be absent.
Septicemic plague usually occurs with the bubonic form as an acute, fulminant illness. Abdominal pain, presumably due to mesenteric lymphadenopathy, occurs in 40% of patients. Pharyngeal plague and plague meningitis are less common forms.
Pestis minor, a more benign form of bubonic plague, usually occurs only in endemic areas. Lymphadenitis, fever, headache, and prostration subside within a week.
The mortality rate for untreated patients with bubonic plague is about 60%, with most deaths occurring from sepsis in 3 to 5 days. Most untreated patients with pneumonic plague die within 48 h of symptom onset. Septicemic plague may be fatal before bubonic or pulmonary manifestations predominate.
Diagnosis
Diagnosis is made by stain and culture of the organism, typically by needle aspiration of a bubo (surgical drainage may disseminate the organism); blood and sputum cultures should also be obtained. Other tests include immunofluorescent staining and serology; a titer of > 1:16 or a 4-fold rise between acute and convalescent titers is positive. PCR testing, if available, is diagnostic. Prior vaccination does not exclude plague; clinical illness may occur in vaccinated people.
Patients with pulmonary symptoms or signs should have a chest x-ray, which shows a rapidly progressing pneumonia in pneumonic plague. The WBC count is usually 10,000 to 20,000/μL with numerous immature neutrophils.
Treatment
Immediate treatment reduces mortality to < 5%. In septicemic or pneumonic plague, treatment must begin within 24 h with streptomycin 7.5 mg/kg IM q 6 h for 7 to 10 days. Many physicians give higher initial dosages, up to 0.5 g IM q 3 h for 48 h. Doxycycline 100 mg IV or po q 12 h is an alternative. Gentamicin is probably also effective. For plague meningitis, chloramphenicol should be given in a loading dose of 25 mg/kg IV, followed by 12.5 mg/kg IV or po q 6 h.
Routine isolation precautions are adequate for patients with bubonic plague. Those with primary or secondary pneumonic plague require strict respiratory isolation.All pneumonic plague contacts should be under medical surveillance. Temperature should be taken q 4 h for 6 days. If this is not possible, tetracycline 1 g once/day po for 6 days can be given, but this can produce drug-resistant strains.
Rodents should be controlled and repellents used to minimize flea bites. Travelers should consider prophylaxis with doxycycline 100 mg po q 12 h during exposure periods.
Other Yersinia Infections
Yersinia
enterocolitica and Y.
pseudotuberculosis occur worldwide and cause human infection.
Y. enterocolitica is a common cause of diarrheal disease and mesenteric adenitis. Y. pseudotuberculosis more commonly causes mesenteric adenitis and has been suspected in cases of interstitial nephritis, hemolytic-uremic syndrome, and a scarlet fever–like illness. Both species can cause pharyngitis, septicemia, focal infections in multiple organs, and reactive arthritis. Mortality from septicemia may be as high as 50%, even with treatment.
The organisms can be identified in standard cultures from normally sterile sites. Selective culture methods are required for nonsterile specimens. Serologic assays are available but difficult and not standardized. Diagnosis, particularly of the reactive arthritis, requires a high index of suspicion and close communication with the clinical laboratory.
Treatment of diarrhea is supportive because the disease is self-limited. Septic complications require β-lactamase–resistant antibiotics guided by sensitivity testing. Prevention focuses on food-handling and preparation, household pets, and epidemiology of suspected outbreaks.
Last full review/revision November 2005
Content last modified November 2005
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