Plague
Plague is a severe infection caused by the gram-negative bacterium Yersinia pestis.
The bacterium that causes plague primarily infects wild rodents, such as rats, mice, squirrels, and prairie dogs. In the past, massive plague epidemics, such as the Black Death of the Middle Ages, killed large numbers of people. Large numbers of rodents and poor sanitation were the major factors contributing to these epidemics. More recent outbreaks have been limited to one person or small clusters of people. More than 90% of the plague infections in the United States occur in the southwestern states, particularly Arizona, California, Colorado, and New Mexico.
The bacteria that cause plague are usually transmitted from infected animals to people by fleas. Coughing or sneezing, which disperse bacteria in droplets, can spread the infection from one person to another. Transmission from household pets, especially cats, can also occur through fleabites or the inhalation of infected droplets.
Symptoms and Diagnosis
Plague takes one of several forms--bubonic, pneumonic, septicemic, or pestis minor. The symptoms vary depending on the form of plague.
Bubonic plague symptoms usually appear 2 to 5 days after exposure to the bacterium, but they can appear any time from a few hours to 12 days later. Symptoms start suddenly with chills and a fever of up to 106° F. The heartbeat becomes rapid and weak, and the blood pressure may drop. Swollen lymph nodes (buboes) appear in the groin, armpit, or neck shortly before or along with the fever. Typically, the swollen lymph nodes are firm and extremely tender. The overlying skin is smooth and red but not warm. The person is likely to become restless, delirious, confused, and uncoordinated. The liver and spleen may enlarge and can be felt easily during examination. Lymph nodes may fill with pus and drain spontaneously during the second week. More than 60% of untreated people die. Most deaths occur between the third and fifth day.
Pneumonic plague is infection of the lungs with plague bacteria that have spread through the blood from another site of infection or that have been inhaled during exposure to a source of the bacteria--such as a person with pneumonic plague who is coughing. This form of plague is highly contagious; experts believe that the pneumonic form could result if plague were disseminated by terrorists. Symptoms, which begin abruptly 2 or 3 days after exposure to the bacteria, include a high fever, chills, rapid heartbeat, and often a severe headache. A cough develops within 24 hours. The sputum is clear at first, but rapidly becomes flecked with blood, and then becomes uniformly pink or bright red (resembling raspberry syrup) and foamy. Rapid and labored breathing is common. Most untreated people die within 48 hours of the start of symptoms.
Septicemic plague is infection that spreads into the blood. Death may occur even before other symptoms of bubonic or pneumonic plague appear.
Pestis minor is a mild form of plague that usually occurs only in a geographic area where the disease is common (endemic). Its symptoms--swollen lymph nodes, fever, headache, and exhaustion--subside within a week.
Plague is diagnosed by analyzing laboratory cultures of bacteria grown from samples of blood, sputum, or lymph nodes.
Prevention and Treatment
Prevention strategies are based on controlling rodents and using repellents to avoid fleabites. Vaccination is no longer available. People who live in, or are traveling to, locations with a plague outbreak may take preventive doses of the antibiotic tetracycline.
When a person is thought to have plague, a doctor begins treatment immediately. Treatment of septicemic or pneumonic plague must start within 24 hours. Prompt treatment reduces the chance of death to less than 5%. Streptomycin injections are given for 10 days; many other antibiotics are effective also.
People with pneumonic plague--unlike those with bubonic plague--must be isolated. Anyone who has had contact with a person with pneumonic plague must be treated or observed closely by a doctor for signs of infection.
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