Current Event Connection

Plague’s Patient Zero?

HEALTH

Scientists may have found the oldest-ever evidence of the plague, locked away in an 20-million-year-old flea. (Washington Post)

See more fleas and other bloodsuckers in our fantastic photo gallery.

This flea is infected with the Y. pestis bacterium, which appears as a dark mass in its gut. How it works: The foregut (proventriculus) is blocked by a Y. pestis biofilm that keeps the flea from being satiated, causing it to feed constantly. (Ultimately, the biofilm prevents digestion and the flea starves.) When the starving flea attempts to feed on an uninfected host, Y. pestis is regurgitated into the wound, causing infection—the plague. Yuk. Photograph courtesy CDC
This flea is infected with Y. pestis bacteria, which appear as a dark mass in its gut. How it works: The foregut (proventriculus) is blocked by a Y. pestis biofilm, or group of sticky microoganisms. The biofilm keeps the flea from being satiated, causing it to feed constantly. (Ultimately, the biofilm prevents digestion and the flea starves.) When the starving flea attempts to feed on an uninfected host (using that long, dark proboscis), Y. pestis is regurgitated into the wound, causing infection—the plague. Yuk.
Photograph courtesy CDC

Discussion Ideas

  • The Washington Post article lists three major infections known as the plague: bubonic plague, pneumonic plague, and septicemic plague. What is the difference?
    • The major difference is where the infection is located.
      • Bubonic plague settles in the lymph system, leading to the telltale “buboes,” or darkened swellings around the lymph nodes of the armpit and groin.
      • Pneumonic plague settles in the lungs. Pneumonic plague is the rarest and deadliest form of plague.
      • Septicemic plague infects the blood.
    • According to WHO: Plague can be a very severe disease, with a case-fatality ratio of 30%-60% if left untreated. (Plague is serious and infectious enough that it is one of only three diseases that should be immediately reported to WHO. Cholera and yellow fever are the other two.) In 2013 there were 783 cases reported worldwide, including 126 deaths. The countries most vulnerable to plague are Madagascar, Democratic Republic of Congo, and Peru.

 

  • What causes human plague?
    • The bacterium Yersinia pestis is responsible for the plague. Although all forms of plague were almost always fatal in the Middle Ages, aggressive antibiotic treatment can be effective for the plague today.

 

  • How is human plague transmitted?
    • Y. pestis has two major vectors. A vector is an organism that carries and transmits disease to another organism. Here is a basic diagram of the Y. pestis cycle, including vectors.
      • The vector in both bubonic plague and septicemic plague is mostly fleas. A person has to be bitten by an infected flea to catch the disease.
      • The vector in pneumonic plague is mostly human beings. Pneumonic plague can be spread simply by the air we breathe.

 

  • Why do scientists think fossilized bacteria found in a 20-million-year-old flea may be related to Y. pestis?
    • The bacteria are physically similar to each other: According to the scientific paper, “of the pathogenic bacteria transmitted by fleas today, Yersinia is the only one that forms both short rods and nearly spherical cells.” The ancient flea’s bacteria are also coccobacilli.
    • The ancient bacteria was found just where scientists would expect to find pathogenic bacteria: around the flea’s proboscis and rectum.
      • The proboscis is the long, tubular mouthpart which the flea uses to drink blood.
      • The rectum is on the other end of the digestive tract and is, ahem, “a standard hangout spot for plague bacteria.”

 

TEACHERS’ TOOLKIT

Washington Post: The history of the Black Death may be locked in this ancient flea

WHO: Plague Factsheet

Nat Geo: Bloodthirsty: Hematophages drink up—on blood

(extra credit!) Journal of Medical Entomology: A New Genus of Fleas with Associated Microorganisms in Dominican Amber

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