by Alisha Golding
I. Etiologic Agent: Yersinia pestis
II. Transmission: The most common mode of transmission is through the bites of infected fleas—which can spread the disease through a species, or allow it to breach the species barrier and infect humans. It can also be contracted by handling plague-infected animals if there is a portal of entry (i.e. break in skin) for the bacteria. Pneumonic plague can be spread by inhaling droplets of infected body fluids that were coughed or sneezed by an infected human or domestic cat. (2)
III. Reservoirs : Wild rodents, including rats, squirrels, prairie dogs, wood rats, and chipmunks. (2)
IV. General Characteristics: Y. pestis is a gram-negative, rod shaped bacterium that is most commonly a vector-borne disease transmitted by the rat flea Xenopsylla cheopis. Y. pestis may develop into one of three forms of plague: (i) Bubonic plague causes buboes, or swelling of the lymph nodes (ii) Septicemic plague occurs when bacteria get into the blood stream and cause shock (iii) Pneumonic plague is caused by infected blood traveling to the lungs
V. Key Tests for Identification
· Fluorescent Antibody Assays
· Agglutination Assays
· Rapid dipstick tests (for field use only) (7)
VI. Signs and Symptoms: Initial signs and symptoms include swollen and tender lymph glands, chills, headache, fever, exhaustion, and a history of contact with rodents or fleas-- usually occurring 2-6 days after initial exposure, and the development of buboes occurring one day after the onset of other symptoms. If the plague arrests in this stage, but goes untreated, the mortality rate is 50-75%, and death occurs within one week of the first onset of symptoms. If bacteria enter the bloodstream and lungs, pneumonic plague develops with the symptoms being overwhelming pneumonia, high fever, cough, bloody sputum, chills. The mortality rate is close to 100% at this stage.
VII. Historical Information
(i) First Pandemic or Justinian’s Plague: Earliest recordings of plague can be seen in the biblical book of I Samuel where it describes how the Philistines were punished for stealing the Ark of the Covenant “with an outbreak of tumors in the groin.” Plague first reached pandemic proportions in 541 AD. It originated either in Ethiopia or in the Central Asian steppes, where it then traveled along the caravan trading routes. As many as 100 million Europeans perished. (4)
(ii) Second Pandemic or The Black Death: Originated in Asia in the 1340s, and was spread by the Silk Road caravan routes. Bubonic plague was the predominant form in Europe, whereas pneumonic plague appeared to be prevalent the Middle East. The estimated population of Europe in 1347 was 75 million; by 1352, the population had declined to 50 million. Plague outbreaks continued until the early 17th century where each of these epidemics had a 10% to 15% mortality rate. (4)
(iii) The Third Pandemic or Modern Pandemic: 1894-1959, originated in China and spread to India, killing about one million people in India in 1903. Subsequently, the plague invaded Java, Japan, Asia Minor, South Africa, the shores of North and South America, Portugal, Austria, and parts of Russia. There were an estimated 26 million plague cases and more than 12 million deaths, the vast majority in India. Plague reached the United States west coast in 1900, and remains endemic in the West and Southwest today. (4)
VIII. Virulence Factors: Y. pestis is able to survive and proliferate inside of phagocytotic cells rather than being destroyed by them. This leads to the proliferation of virulent organisms which can overwhelm the host’s immune system.
IX. Control and Treatment: As soon as plague is suspected, patients should be isolated and public health departments notified. Blood cultures can be screened using a rapid diagnostic test that detects the capsular antigen of Y. pestis. Drug therapy should begin immediately using prophylactic antibiotics such as streptomycin and tetracycline. People who may have come in contact with the infected person or surroundings should be immediately vaccinated, or given preventative antibiotic therapy. (1)
X. Preventions and Vaccines: Plague is endemic in the far West and Southwest of the U.S.; therefore, prevention is focused on reducing the spread of the disease to humans in high risk areas through 3 techniques:
(i) Environmental Management: Close surveillance for infected animals in endemic areas, as well as using insecticides to preventatively control rodent flea proliferation. (7)
(ii) Public Health Education: Educating residents of endemic areas how to eliminate food and shelter for rodents around places of work, home, recreation—specifically, eliminating rock piles, junk, and open pet foods around these areas. Also, educating citizens to report dead/sick rodents to health department immediately as well as treating domestic pets for fleas on a regular basis. (7)
(iii) Preventative Drug Therapy: If there is a possibility of exposure to plague, antibiotics such as tetracycline, chloramphenicol should be administered immediately. (7)
XI. Local Cases and Statistics:
· WHO reports a yearly average of 10 to 20 plague cases within the U.S.
· In 2008, 1482 suspected animals were tested for plague within the state of Texas. 75 of those animals were positive for plague—with coyotes and raccoons being the highest contributors to this statistic. There were no reported cases in Travis or Williamson counties. (5)(6)
XII. Global Cases and Statistics
· Approximately 23,278 cases of human plague were reported between 1998-2008
o 2116 fatalities in 11 countries.
o 95% of these cases were reported from Africa.
· WHO reports an annual average of 1,000 to 3,000 global cases. (7)
· This disease may have caused over 200 million deaths in the history of humanity. (4)
· Significant plague foci exist in Asia, Africa and in North and South America. (7)
1. “Plague”. 29 June 2009 Center for Disease Control and Prevention. 10 May 2010 http://www.cdc.gov/ncidod/dvbid/plague/index.htm
2. “FAQ About Plague”. 05 April 2005 Center for Disease Control and Prevention. 10 May 2010 http://emergency.cdc.gov/agent/plague/faq.asp
3. “Plague and Animals” 20 June 2009 Center for Disease Control and Prevention. 10 May 2010 http://www.cdc.gov/healthypets/diseases/plague.htm
4. “History of Plague—Plague Through the Ages”. 30 March 2007 Texas Department of State Health Services. 10 May 2010 http://www.dshs.state.tx.us/preparedness/bt_public_history_plague.shtm
5. “Plague Confirmed in West Texas Prairie Dogs”. 06 July 1998 Texas Department of Public Health. 10 May 2010 http://www.dshs.state.tx.us/idcu/health/dpn/issues/dpn58n14.pdf
6. “Plague Surveillance Report”. 2008 Texas Department of Public Health. 09 May 2010 http://www.dshs.state.tx.us/idcu/disease/plague/information/Reports/Plague08.pdf
7. “FAQ on Plague”. June 2009 World Health Organization. 10 May 2010 http://www.searo.who.int/LinkFiles/CDS_FAQ_Plague.pdf
8. “Plague”. February 2005 World Health Organization. 09 May 2010 http://www.who.int/mediacentre/factsheets/fs267/en/