By Michelle Li
Published 8:21 EST, Mon August 30, 2021
Introduction and History
The plague is a disease that is caused by the bacterium Yersinia Pestis. The Black Death, one of the most notable pandemics in history, was a result of the transmission of Y. pestis from rats and fleas to humans, making it a zoonotic disease (Frey, “Plague). This transmission often occurred through flea bites or contact with the body fluid of an infected animal. The plague takes on three different forms depending on the affected area of the body: bubonic (affecting lymph nodes), pneumonic (affecting the lungs), and septicemic (affecting the blood). The Black Death is characterized by both the swelling of lymph nodes, which turn black as a result of bubonic plague, and the blackening of skin, resulting from septicemic plague (Frey, “Plague). An estimated 75 to 200 million lives were lost before the end of the Black Death (Frey, “Bubonic Plague”). Today, the number of fatalities resulting from (and cases of) the plague are not even remotely close to the numbers seen during the Black Death; the recorded numbers are not zero, however.
Plague in the modern day
Cases of the plague, although much less frequent, still exist today. A majority of the present day cases of the plague occur in developing countries. In fact, the plague is still endemic to (regularly found in) Madagascar, Peru, and the Democratic Republic of the Congo (Frey, “Bubonic Plague). Madagascar reports more plague cases than any other single country, averaging 200 to 400 cases every year (Hardman).
A portion also occurs in the United States. The Centers for Disease Control and Prevention (CDC) reports between 1 to 17 cases of the plague each year in the United States (with an average of 7 reported cases per year). Plague in the United States occurs in western, rural areas; northern New Mexico, northern Arizona, southern Colorado, California, southern Oregon, and western Nevadea are the most affected regions. 80% of these U.S. cases are in bubonic form (“Plague in the United States”).
Figure 1: This figure shows a world map of plague cases reported to the World Health Organization (WHO) by country between 2000 and 2009 (Centers for Disease Control and Prevention)
There are about 5,000 cases of the plague reported to the World Health Organization (WHO) each year worldwide, and 95% of these cases occur in Africa. Interestingly, the only two continents that are plague-free are Australia and Antarctica (Frey, “Plague”).
More “recent” plague outbreaks include an outbreak of pneumonic plague in Surat, India in 1994, where 876 cases of infections, including 52 deaths, were reported to the WHO (Frey, “Plague”). The most recent outbreak in Madagascar occurred in 2017 and resulted in 2,575 confirmed or probable cases of bubonic and pneumonic plague, including 221 deaths (World Health Organization 2017). Even more recently, the WHO began reporting on an ongoing outbreak of suspected pneumonic plague in the Dominican Republic of Congo in January of 2020. As of May 2021, there are a total of 564 suspected pneumonic plague cases, including 43 deaths (World Health Organization 2021).
Today, the plague is treatable with antibiotics. 80% to 90% of patients with bubonic plague that received rapid diagnosis and appropriate treatment will survive; the survival rates for septicemic plague and pneumonic plague are lower in comparison at 75% and 50%, respectively (Frey, “Bubonic Plague”). If left untreated however, each form of the plague is still fatal a majority of the time. Bubonic plague has a mortality rate of 60% to 70% in untreated cases, while untreated septicemic and pneumonic plague both have a mortality rate of 100%. Pneumonic plague, specifically, is 100% fatal if left untreated for 48 hours (Frey, “Bubonic Plague”).
Streptomycin, an antibiotic discovered in the 1940s, is one of the first-line treatments for plague (Hardman). Gentamicin, chloramphenicol, and tetracycline are alternatives that can also be administered. It is important that the administration of antibiotics is started as soon as possible (Cua).
Some scientists have also considered the association between climate and plague. The conditions following warmer weather in the spring and wet weather in the summer are beneficial for fleas and bacteria, which play key parts in the spread of plague (Hardman). Additionally, outbreaks of plague among local animals (called epizootics) most commonly occur after wet winters and cool summers; these epizootics could also affect humans (Frey, “Plague”). In the case of the plague outbreak in Surat, India, rainfall also influenced the spread of plague, as flooding increased contact with drowned, infected animals that were not disposed of (Frey, “Plague”). Similarly to other climate sensitive and infectious diseases, the effects of global warming may increase the number of outbreaks of plague in animals and, in turn, in human populations (Hardman).
Lastly, the animal reservoirs of the plague (the host animal populations that infectious diseases survive off of) make the disease impossible to eradicate (Frey, “Plague”). Rats play a large role in the spread of the plague. Controlling that spread—considering their sheer numbers and the scope of human capabilities—proves to be near impossible. Surveillance of animal populations and careful reporting of plague cases, however, is still important in preventing plague (Frey, “Plague”).
The plague is an infectious disease that is well known due to its connection to the Black Death, one of the most notable epidemics in history. While the occurrence of the plague has changed since medieval times, the high mortality rates of untreated plague cases have remained and are currently affecting different regions of the world. Considering its connections to climate change and recent developments, the plague is not a disease of the past, but rather, one that is still relevant to the modern world.
Michelle Li, Youth Medical Journal 2021
Centers for Disease Control and Prevention. “World Plague Map – 2000 to 2009 – CDC.” Wikimedia Commons, commons.wikimedia.org/wiki/File:World_Plague_Map_-_2000_to_2009_-_CDC.jpg. Accessed 30 June 2021. Map.
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