Plague is a term applied to an infectious disease that spreads easily and, without antibiotics treatment, can be fatal. The plague has caused more fear and terror than perhaps any other infectious disease in history. It has killed nearly 200 million people and has produced monumental changes, such as marking the end of the Dark Ages and causing the advancement of clinical research in medicine.
  • Although still debated by historians, the plague has been responsible for multiple epidemics and at least 3 great pandemics (epidemics that are spread over a large region or multiple sections of the world).


- The first plague pandemic spanned from the Middle East to the Mediterranean basin during the 5th and 6th centuries, killing about half the population of those areas.

- The second pandemic struck Europe between the 8th and 14th centuries, destroying nearly 40% of Europe's population.
- The third pandemic started in 1855 in China and spread to every major continent.   
  • Alexandre Yersin isolated the bacterium (germ) that causes plague, developed a treatment (an antiserum) to combat the disease, and was the first to suggest that fleas and rats may have been spreading plague during theepidemic of 1894. The plague bacillus (bacterium) was named Yersinia pestisin Yersin's memory.
  • Pandemics have succeeded in spreading the plague to every major continent, with the possible exception of Australia. Unlike smallpox, the plague cannot be wiped out. It lives in millions of animals and on billions of the fleas that live on those animals. The plague is a disease of the desert, the steppes, the mountains, and the forest.
        - In the US, an average of 18 cases per year has been reported during the last few decades. These cases are the mildest form of the illness, and they occur mostly in the Southwest. Prairie dogs of the southwestern plains had once died from the plague. A certain type of squirrel may be vulnerable to contracting the plague in some western states, such as New Mexico, Arizona, Colorado, Utah, and California. Only one case of imported plague has been reported since 1926.
      - Outside the United States, the World Health Organization has reported an annual average of 1,666 cases from 1967-1993. The number of actual cases is probably much higher because many countries fail to diagnose and report the plague. The following countries have reported the most cases of humans infected with the plague since 1979 (in order of most reported cases): Tanzania, Vietnam, Zaire, Peru, Madagascar, Burma, Brazil, Uganda, China, and the US.


The symptoms of plague can be progressive; however, most investigators break the symptoms into three different groups because plague is often described in three types; bubonic, septicemic, and pneumonic. A patient can also present with the symptoms of only one type of plague.


Untreated plague may show progressive symptoms that can overlap; however, the following will describe those symptoms and signs that predominate during the three general types of plague:

  • Bubonic: In about three to seven days, lymph nodes become swollen, tender, and are termed buboes (the termbubonic is derived from buboes) and the patient may also develop fever, chills, and weakness.
  • Septicemic: In general, septicemic plague patients do not develop buboes; instead symptoms may include fever, chills, weakness, bleeding under the skin, abdominal pain, and septic shock with low blood pressure. Septicemic plague may develop in about one to seven days after exposure.
  • Pneumonic: In about one to three days after the person is exposed to airborne droplets that contain Y. pestis, shortness of breath, cough(sometimes with bloody sputum), and chest pain quickly develop along with weakness, fever, and headaches.


Untreated bubonic plague may progress and produce symptoms of both septicemic and pneumonic plague, while septicemic plague may progress to produce pneumonic plague. However, pneumonic plague is the most serious and lethal form of plague, and while the patient may develop septicemic symptoms, the pneumonic symptoms are the most serious. Nonetheless, all three plague types can be fatal to a patient.


Infection with Y. pestis causes plague in humans. Y. pestis is a bacterium that is gram-negative rod-shaped bacterium genetically related to Escherichia coli that resembles a "safety pin" when stained with chemicals and viewed with a microscope.


In general, plague circulates in rodent populations where infected fleas on rodents transfer the bacteria to other rodents. When the rodent population invades human habitats or when humans invade rodent habitats, the infected fleas on the rodents will also bite humans.


This flea bite begins plague in an individual. However, once a human is infected, it is fairly easy for that person to infect other people with the organisms especially if they develop pulmonary infection because droplets containing Y. pestis from the lungs are expelled into the air and can infect other humans.


How is plague spread?


Plague is a zoonotic (animal to animal) disease that can be spread to humans by several methods. The usual way humans encounter plague is from getting a flea bite from a flea that has previously been infected from biting an animal where the disease is endemic. Most often this is attributed to a plague-infected rat population, but it could be from many other animals such as mice, prairie dogs, squirrels, and other rodents. Unfortunately, even domestic cats and dogs can become infected and potentially may transmit the disease to humans.


Dead animals can still contain many viable Y. pestis; humans can become infected when they handle these animals; people should use caution when touching touch dead animals or even getting close to them as they may have fleas looking for another warm (human) body to bite. Human-to-human spread is easily done by people with pneumonic plague as they can spread infected droplets expelled from the lungs to other people or to objects that are subsequently touched by others.


Individuals with bubonic or septicemic plague can also transmit the disease, usually by direct or indirect contact with infected body fluids or objects that come in contact with these fluids. Spread of plague can be facilitated when conditions arise that encourage rat populations to rapidly increase. For example, when cities reduce or fail trash pickup for any extended time period, a rat population may flourish, and so may the flea population.


Consequently, human behaviors (warfare, economic failures, urban expansion, and others) may augment the development of plague.


What is the treatment for the plague?


Currently, plague is treated with antibiotics. The following antibiotics have been used to successfully treat plague if the person's disease has not yet overwhelmed the body's defenses (earlier treatments have a better chance to stop the disease):

  • Streptomycin.
  • Gentamicin (Garamycin).
  • Chloramphenicol.
  • Tetracyclines (Sumycin).
  • Fluoroquinolones.


Patients who are suspected of being exposed to plague should be treated immediately. The antibiotic, route of administration (IV or oral), duration of treatment and supportive care, if necessary, are determined by the patient's caregiver and usually in consultation with CDC or infectious-disease specialists.


Plague is rarely seen in the U.S. (about 13 infections diagnosed per year with one recent year with 40 diagnosed); however, about 14% of people who are diagnosed in the U.S. still die from the disease. The World Health Organization estimates about 2,900 individuals per year are diagnosed with plague currently.


How can plague be prevented?


The CDC provides the following preventive recommendations related to zoonosis diseases caused by rodents and their vectors, including plague:

  • Watch for plague activity in rodent populations where plague is known to occur. Report any observations of sick or dead animals to the local health department or law-enforcement officials.
  • Eliminate sources of food and nesting places for rodents around homes, work places, and recreation areas; remove brush, rock piles, junk, cluttered firewood, and potential-food supplies, such as pet and wild animal food. Make your home rodent-proof.
  • If you anticipate being exposed to rodent fleas, apply insect repellents to clothing and skin, according to label instructions, to prevent flea bites. Wear gloves when handling potentially infected animals.
  • If you live in areas where rodent plague occurs, treat pet dogs and cats for flea control regularly and not allow these animals to roam freely.
  • Health authorities may use appropriate chemicals to kill fleas at selected sites during animal plague outbreaks.
  • To avoid potential risk of exposure to hantavirus infection,

- safely clean up rodent-infested areas;

- air out infested spaces before cleanup;

- spray areas of infestation and all excreta, nesting, and other materials with household disinfectant or 10% bleach solution then clean up, seal in bags, and dispose;

- avoid sweeping, vacuuming, or stirring dust until the area is thoroughly wet with disinfectant;

- and wear rubber gloves; disinfect gloves before removal, and wash hands after ward.


Prophylactic (preventive) antibiotics:


Health authorities advise that antibiotics be given for a brief period to 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 bacterium.


Such experts also recommend that antibiotics be given if a person has had close exposure to a person or an animal (for example, a house cat) with suspected plague pneumonia. 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.

The preferred antibiotics for prophylaxis against plague are the tetracyclines or the sulfonamides. There is no commercially available vaccine against plague available in the U.S.

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