Wednesday, 25 February 2009

Yersinia pestis

Yersinia pestis (formerly Pasteurella pestis) is a Gram-negative rod-shaped bacterium belonging to the family Enterobacteriaceae. It is a facultative anaerobe that can infect humans and other animals.

Also known as the plague, Y. pestis ravaged the European population through the dark ages (Justinian’s plague 541-767 AD) arriving from East and central Africa, spreading to most of the Mediterranean (1), and most of the Middle Ages radiating out from the Caspian Sea. Between the years 1347-1353 plague caused the death of one third of the European population, making it one of the most deadly of all human diseases. First characterized by Yersin in 1894 during the final plague pandemic, which spread out from the Yunnan region of China (ref 2 3).

Primarily a disease of rodents or other wild mammals that usually transmitted by fleas and often is fatal. Human disease is now rare but is usually contracted through contact with rodents and their fleas.
Y. pestis is split into three biovars; Antiqua, Medievalis, and Orentalis, based on small phenotypic differences. Each biovar has been attributed to a particular pandemic event; Antiqua to Justinian’s plague, Medievalis to, resident in central Asia to the pandemics of the middle ages and finally Orentalis to the final Yunnan pandemic of 1894 (4).

Recent DNA-DNA hybridization studies have revealed that Y. pestis is highly related to Y. pseudotuberculosis with the 16s rRNAs being an exact match.
Y. pestis and Y. pseudotuberculosis differ in the diseases that they cause, Y. pestis causes fatal bubonic plague and is transmitted by flea bites or person to person (pneumonic plague), whilst Y. pseudotuberculosis is transmitted person to person through fecal-oral route and rarely results in death.

Symptoms differ depending on the type of Y. pestis infection bubonic, septicemic and pneumonic (5).

Bubonic plague
There is an incubation period of 2-6 days, whilst the bacteria replicate in the lymph nodes. This s followed by lethargy, fever, headache and chills occur suddenly at the end of the incubation period. From this point the infection is resolved or lethal. There will also be the characteristic swelling of lymph nodes resulting in buboes; this is the classic sign of bubonic plague

Septicemic plague
Following the initial incubation period symptoms that may arise include, hypotension, hepatosplenomegaly, delirium, seizures in children, shock, fever. The other symptoms of Bubonic or Pneumonic Plague, not always present

Pneumonic plague
Characterised by Fever, Chills, Cough, Chest pain, dyspnea, hemoptysis, lethargy, hypotension and shock.

Y. pestis can now be treated with standard antibiotic therapies but there is evidence of resistant strains emerging

  1. Brossollet J, & Mollaret H (1994) Pourquoi la peste? Le rat, la puce et le bubon (Gallimard, Paris, France).
  2. Yersin A (1894) Ann Inst Pasteur 2:428430.
  3. Perry R D &Fetherston J D (
    Perry, R.D.,, Fetherston, J.D. (1997). Yersinia pestis--etiologic agent of plague Clinical Microbiology Reviews DOI: 8993858
  4. Devignat, R. (1951). Varieties of Pasteurella pestis; new hypothesis. Bulletin of the World Health Organization 4:247263, pmid:14859080.

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