What is it

Plague is an infectious disease of animals and humans caused by a bacterium named Yersinia pestis. People usually get plague from being bitten by a rodent flea that is carrying the plague bacterium or by handling an infected animal. Millions of people in Europe died from plague in the Middle Ages, when human homes and places of work were inhabited by flea-infested rats.

There are three types of the plague: bubonic, pneumonic, and septicemic. Bubonic plague is the most common form of plague. It occurs when an infected flea bites a person or when materials contaminated with the bacteria enter through a break in a person's skin. This form of plague does not spread from person to person. Septicemic plague occurs when the bacteria multiply in the blood. It can be a complication of the pneumonic or bubonic plague or can occur by itself. When it occurs alone, it is caused in the same way as bubonic plague. Pneumonic plague occurs when the bacteria infect the lungs. Transmission can take place if someone breathes in aerosolized bacteria or by breathing in the respiratory droplets of a person or animal with the disease. It may occur if bubonic or septicemic plague is untreated and the bacteria spread to the lungs.

Plague's history as a biological weapon dates to World War II, when a secret branch of the Japanese army was reported to have dropped plague-infected fleas over China causing outbreaks. Both the United States and the Soviet Union then developed techniques to aerosolize plague. The U.S. program was terminated in 1970.

Syntoms

The sign that plague is present is a very painful, usually swollen and often hot-to-the touch lymph node, called a bubo. Onset of bubonic plague is usually two to six days after a person is exposed. Symptoms of bubonic plague are muscular pain, high fever, chills, headaches, swelling of lymph glands (called buboes) in the armpits, neck, groin and other areas. In some cases, seizures can occur. Symptoms for septicemic plague can include nausea, vomiting, fever, low blood pressure, chills, abdominal pain, shock and bleeding into skin and other organs. The incubation period of primary pneumonic plague is one to three days and is characterized by development of an overwhelming pneumonia with high fever, cough, bloody sputum and chills.

Testing

A patient suspected to have plague should be hospitalized and isolated. Testing would include examining blood cultures for plague bacteria and a microscopic examination of lymph gland. Sputum samples also would be evaluated.

Recovery Potential

If treated immediately, a full recovery is possible. The risks of death become higher the longer symptoms go untreated. For plague pneumonia patients, the death rate is more than 50 percent.

Prevention/Treatment

Attempts to eliminate fleas and wild rodents from the natural environment in plague-infected areas are impractical. However, controlling rodents and their fleas around places where people live, work, and play is very important in preventing human disease. Eliminate sources of food and nesting places for rodents; remove brush, rock piles, junk, cluttered firewood, and potential food supplies, such as pet and wild animal food. If you anticipate being exposed to rodent fleas, apply insect repellents to clothing and skin to prevent flea bites.

Health authorities advise that antibiotics be given for a brief period to people exposed to someone with pneumonic plague. They also suggest treating people who have been exposed to the bites of potentially infected rodent fleas (for example, during a plague outbreak) or who have handled an animal known to be infected with the plague bacteria. People who must be present in an area where a plague outbreak is occurring can protect themselves for two to three weeks by taking antibiotics, such as the tetracyclines or the sulfonamides. Plague vaccine has very limited use and is administered to scientists who routinely work with the plague bacteria and people in plague-infested areas who handle or have close contact with potentially infected animals as part of their routine work (such as rodent biologists).

Environmental Cleanup

Plague is best prevented by controlling rat populations in both urban and rural areas. This goal has been reached in the cities, towns, and villages of most developed countries. It has not been achieved in either the rural or urban areas of many developing countries where the threat of epidemic plague continues to exist. If you live in areas where rodent plagues occur, treat pet dogs and cats for flea control regularly and do not allow them to roam freely. Health authorities may use appropriate chemicals to kill fleas at selected sites during animal plague outbreaks.