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Yersinia Pestis Bacteria

Incubation Period

Once a person becomes infected with Yersinia pestis, the bacteria begin to multiply within the body. When a person has bubonic plague, the bacteria multiply in the lymph system; with pneumonic plague, this occurs within the lungs. (The lymph, or lymphatic system, is a major component of your body's immune system. The organs within the lymphatic system are the tonsils, adenoids, spleen, and thymus.) Within one to six days, symptoms of plague can begin. The period between becoming infected and the start of symptoms is called the plague incubation period.


For each type of plague, there are different symptoms. It is possible for a person to have symptoms of only one type, while it is also possible for a person to experience symptoms from each of the types. For example, a person may first develop bubonic plague symptoms, followed several days later by septicemic plague symptoms, and then pneumonic plague symptoms.
(Click Symptoms of Plague or Pictures of Plague to learn more about plague symptoms.)

Making a Diagnosis

In order to make a Yersinia pestis diagnosis, the doctor will ask a number of questions about a person's medical history and perform a physical exam. During the exam, the doctor will look at the skin and listen to the lungs for signs of plague. The doctor may recommend certain tests if he or she believes that the patient is infected with Yersinia pestis bacteria.
Given that there are a number of conditions that share similar symptoms of plague, the doctor will consider these and rule them out before making a firm diagnosis. These conditions can include:
  • Syphilis (a sexually transmitted disease)
  • Lymphogranuloma vernereum (a sexually transmitted disease affecting the lymph system)
  • Hernia
  • Appendicitis
  • Cat scratch fever (a disease associated with being scratched by a cat)
  • Tularemia (a serious illness usually caused by animals)
  • Typhoid fever (a life-threatening illness caused by Salmonella)
  • Shigellosis (an infectious disease typically caused by unsanitary conditions).

Plague Disease

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