Wednesday, December 20, 2006

What is the plague, anyway?

Well, it's a disease. A really, really bad disease, caused by fleas vomiting infected blood into open wounds. Gross, no?

Plague can take many forms:
  • Bubonic plague occurs when Yersinia pestis (a bacterium) causes an inflammation of the lymph nodes, making them tender and swollen. This is the most common form of plague. Bubonic plague becomes evident three to seven days after the infection. Initial symptoms are chills, fever, diarrhea, headaches, and the swelling of the infected lymph nodes, as the bacteria replicate there. If untreated, the rate of mortality for bubonic plague is 50%.

  • Cellulocutaneous plague is a very unusual form, with Yersinia pestis causing a skin infection.

  • Pneumonic plague or pulmonic plague occurs when the lungs are infected by Yersinia pestis. It is the second most common form of plague. It may be a secondary infection, caused by bacteria spreading from the lymph nodes and reaching the lungs, but can also exist on its own, caused by inhalation of airborne bacteria. With this infection comes the possibility of person-to-person transmission through respiratory droplets. The incubation period for pneumonic plague is usually between two and four days, but can be as little as a few hours. The initial symptoms, of headache, weakness, and coughing with hemoptysis, are indistinguishable from other respiratory illnesses. Without diagnosis and treatment, the infection can be fatal in one to six days; mortality in untreated cases may be as high as 95%.

  • Meningeal plague or plague meningitis looks like meningitis at the outset. It is most common in children and is usually the end result of ineffective treatment for other forms of plague. It is highly unusual.

  • Pharyngeal plague occurs when Yersinia pestis is consumed, often through food. It can resemble tonsillitis. It is a very rare form of the plague.

  • Septicemic plague occurs when Yersinia pestis multiply in the blood. It is the third most common form of plague. It is usually associated with hunting and skinning of animals, but can also occur secondary to bubonic and pneumonic plague. This type of plague is characterized by bleeding into the skin and other organs, which creates black patches on the skin. There are bite-like bumps on the skin, commonly red and sometimes white in the center. Untreated septicemic plague is universally fatal, but early treatment with antibiotics reduces the mortality rate to 4 to 15%. People who die from this form of plague often die on the same day symptoms first appear.

  • Other forms of plague (Aliae formae pestis) include the milder forms abortive plague, asymptomatic plague and pestis minor, all three often resulting only in a mild fever and light swelling of the lymph glands, usually resolved in approximately a week if appropriate treatment is given.

Plague is primarily a disease of rodents. Infection most often occurs when a person is bitten by a rat or flea that has fed on an infected rodent. The bacteria multiply inside the flea, sticking together to form a plug that blocks its stomach and causes it to become very hungry. The flea then voraciously bites a host and continues to feed, even though it is unable to satisfy its hunger. During the feeding process, blood cannot flow into the blocked stomach, and consequently the flea vomits blood tainted with the bacteria back into the bite wound. The Bubonic plague bacterium then infects a new host, and the flea eventually dies from starvation. Any serious outbreak of plague is usually started by other disease outbreaks in rodents, or some other crash in the rodent population. During these outbreaks, infected fleas that have lost their normal hosts seek other sources of blood.

Sources: Wikipedia, Manual of Common Diseases and Parasites of Wildlife in Northern British Columbia

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