Evolution of Yersinia Pestis, the Bacteria that Causes the Bubonic Plague

Introduction Yersinia pestis is a bacterium that causes the bubonic plague, in which one of its well-known symptoms is swollen lymph nodes called buboes to appear on the body (Perry and Fetherson 1999). Yersinia pestis evolved from clones of Y. pseudotuberculosis within the last 1,500 to 20,000 years, where it evolved separate times in China (Achtman et al. 1999). Yersinia pestis is spread through fleas feeding on infected and uninfected blood as well as open wound contact with infected blood (Titball et al. 2003).

Symptoms and Proximate Causes Initially, after two to six days of infection, victims start to develop fever, headache, chills and buboes that appear around the body (Perry and Fetherson 1999). Buboes are swollen lymph glands that feel smooth and soft but are painful to the touch (Perry and Fetherson 1999). These buboes usually appear around the armpits and neck, though they can also appear around the groin (Perry and Fetherson 1999). There is also a chance for pain to happen in the lymph node before the bubo starts to appear (Perry and Fetherson 1999). Skin lesions and bacteria in the blood can also occur among bubonic plague victims, as well as gastrointestinal disorders such as nausea, diarrhea and vomiting (Titball et al. 2003; Perry and Fetherson 1999). The proximate cause for the bubonic plague is an infection in the lymph nodes by Y. pestis (Perry and Fetherson 1999). Yersinia pestis is spread through the bites of fleas and rodents infected by it or exposure of open wounds to other possible reservoirs of infection (Perry and Fetherson 1999).

Evolutionary History Yersinia pestis evolved from clones of Y. pseudotuberculosis, a low-grade enteric pathogen, within the last 1,500 to 20,000 years (Achtman et al. 1999)...

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