The Bubonic Plague (Yersinia Pestis): "The Black Death"

By: Lori M. Netahlo-Barrett

"Not such were they as in the East, where an issue of blood from the nose was a manifest sign of inevitable death; but in men and women alike it first betrayed itself by the emergence of certain tumors in the groin or the armpits, some of which grew as large as a common apple, others as an egg, some more, some less..."

Giovanni Boccaccio "The Decameron"

This is how Giovanni Boccaccio, an Italian writer in Florence, described the most devastating epidemic that spread across Europe in 1348, taking one-third of the population with it. We call it the bubonic plague, though in the nineteenth century, historians named it the Black Death for the black blotches that appeared on the skin.

"The Black Death of 1348-50 was the greatest biomedical disaster in European and possibly in world history. A third at least of Europe's population died...this means that somewhere around twenty million people perished..." (Cantor, 2002, p. 6).

A Brief History of the Plague

Although still debated by historians, the plague has been responsible for at least three great pandemics and multiple epidemics in history. The first pandemic, known as the Justinian plague (541-544 CE), began in Egypt and spread throughout the Middle East and Mediterranean areas. Eventually, the entire known world was affected. By the 8th century, plague receded into scattered endemic areas. The second pandemic began in 1347, when traders from central Asia (via the Silk Road) introduced plague into ports of Sicily. Several Italian merchant ships returned from a trip to the Black Sea, one of the key links in trade with China. When the ships docked in Sicily, many of those on board were already dying of plague. Within days, the disease spread to the city and the surrounding countryside. This became the first epidemic, known as the Black Death.

The third pandemic began in Hong Kong in 1894 and continues to the present. Alexandre Yersin discovered the plague bacillus, Yersinia pestis, and effective antibiotics were introduced in the early 1940s; however, plague remains endemic in many parts of the world.

"The Black Death affected most parts of the Mediterranean world and Western Europe...but the great medical devastation hit no country harder than England...there were at least three waves...falling upon England over the century following 1350...." (Cantor, 2002, p. 7).

Those who survived the Black Death believed that there was something special about them -- almost as if God had protected them. The Catholic Church promised cures, treatment, and an explanation for the pestilence. They said it was God's will, but the reason for this awful punishment was unknown. People prayed to God for forgiveness but the Black Death was an unforgiving and formidable enemy.

The Organism and the Disease

The organism Yersinia pestis is in the bacillus family (meaning rod shaped) of bacterial zoonosis. Bacillus bacteria are present in nature and can form spherical spores when conditions are stressful for it in order to survive in a dormant stage for extended periods.

The bacillus is transmitted from a carrier (in this case the rat) to a human via the bite of a vector. In the epidemic of 1348, the vector was the oriental rat flea. The flea does not cause the disease itself but it spreads the disease by conveying pathogens from one carrier to another. The common form of transmission during this time was by a bite of a vector that was infected by the carrier (the rat).

The Black Death or "pestilence," appeared in three forms: bubonic, pneumonic, and septicemic. Each form was transmitted in two ways. The septicemic and bubonic plagues were transmitted with direct contact with a flea, while the pneumonic was transmitted through airborne droplets of saliva coughed up by bubonic or septicemic infected humans. With the three forms of the disease running rampant, it is easy to understand how and why the Black Death spread so rapidly and with such devastation.

When an infected flea feeds on a host, the bacterium multiplies in the gut of the flea, blocking its stomach and causing it to become very hungry. The flea would voraciously bite its host and continue to feed because it was unable to satisfy its hunger. During the feeding process, infected blood carrying the bacillus flows into the wound. The flea would eventually die from starvation.

"Rodents resistant to the infection form an enzootic stage that ensures the long-term survival of the bacillus. Occasionally, the infected animals are not resistant to the disease and die. This is known as an epizootic stage and ensures the spread of the organism to new territory." (Velendzas, 2004, p. 1).

Symptoms and Pathology

The incubation period is normally 2-6 days but this can vary with the individual. One of the first symptoms to appear in those affected with the bubonic form of the disease is a sudden onset of high fever, chills, and headache. It is followed by body aches, extreme exhaustion, and abdominal pain. Painful lymph node swelling called buboes appear in the groin and armpits, which ooze pus and blood. The victim would bleed under the skin until they were covered in black blotches. The mortality rate in untreated cases was between 40-60%.

The second most commonly seen form was the pneumonic strain. This variance is contracted airborne and is highly contagious. As with the other two strains, there is an abrupt fever and chills. A cough and severe chest pain follows. Thin, watery, blood-tinged sputum becomes bloody as the disease rapidly progresses.

Buboes may or may not appear in this strain. This variance had a 100% mortality rate if not treated within the first twenty-four hours of infection. To date, the mortality rate for this strain is still nearly 100% fatal.

With the septicemic variation of the disease, which is observed mostly in the elderly, is the rarest form, with a rapid onset of those symptoms like the bubonic form without the buboes. Symptoms included a high fever. There is a 100% mortality rate in untreated cases with this strain due to the high level of bacillus in the blood.

Although medical science has made tremendous leaps since the Middle Ages, those that survive the onset of plague may perish due to complications such as septic shock, lung abscesses, and super infection of buboes or meningitis.


The Black Death showed no favoritism with respect to age and sex and it could be contracted during any season of the year. Those most susceptible, as with many infectious diseases were the weak and elderly. We do know that during the medieval period many urban cities were overpopulated with individuals living very close together. For many peasants malnourishment, disease, and poor health were part of daily life. Medicines available were often useless and no one knew what caused disease.

Towns were mostly filthy and knowledge of hygiene was non-existent. The disposal of bodies was very crude and helped spread the disease still further as those who handled the dead did not protect themselves from infection. The filth that littered streets gave rats the perfect breeding environment.

"Outbreaks in people still occur in rural communities or in cities. They are usually associated with infected rats and rat fleas that live in the home. In the United States, the last urban plague epidemic occurred in Los Angeles in 1924-25. Since then, human plague in the United States has occurred as mostly scattered cases in rural areas (an average of 10 to 15 persons each year). Globally, the World Health Organization reports 1,000 to 3,000 cases of plague every year" (CDC, 2004, ¶ 2). With the wonders of modern medicine today, 1 in 7 cases (or 14%) are fatal as opposed to the high mortality rate of 40 to 75% in 1348.


Cities hardest hit during the outbreak of 1348-1350 tried to take measures to control an epidemic no one understood. "In Milan, to take one of the most successful examples, city officials immediately walled up houses found to have the plague, isolating the healthy in them along with the sick. Venice took sophisticated and stringent quarantine and health measures, including isolating all incoming ships on a separate island. But people died anyway, though fewer in Milan and Venice than in cities that took no such measures" (Knox, 1995, p. 9).

In the United States an average of 10 to15 cases per year have been reported in the last few decades. An individual suspected of having bubonic plague is immediately quarantined. Medical care workers can diagnosis an infection of Yersinia pestis by performing a complete blood count. A white blood count may be elevated to levels of 20,000 or greater. The bacillus bacteria grows on most culture media however, growth is slow and may require 48 hours to identify colonies.

Other laboratory tests than can be performed to positively test for the bacillus is chest radiographs, which show the presence of pneumonic plague. In conducting a gram stain, 70% of patients tested, a bipolar 'safety pin' structure of the bacillus may be identified.

Once the patient is diagnosed, most are treated successfully with the use of modern antibiotics such as Gentamicin or Streptomycio. Incision and drainage of buboes may be necessary. Material Drained from the bubose is infectious until the patient is treated appropriately.

Prevention and Control

Outbreaks in populace occur in areas where housing and sanitation conditions are poor. These outbreaks can occur in rural communities or in cities. They are usually associated with infected rats and rat fleas that live within the home.

"Effective environmental sanitation reduces the risk of persons being bitten by infectious fleas of rodents and other animals in places where people live, work, and recreate. It is important to remove food sources used by rodents and make homes, buildings, warehouses, or feed sheds rodent-proof. Applying chemicals that kill fleas and rodents is effective but should usually be done by trained professionals. Rats that inhabit ships and docks should also be controlled by trained professionals who can inspect and, if necessary, fumigate cargoes" (CDC, 2004, ¶ 2).

"Health authorities advise that antibiotics be given for a brief period to people who have been exposed to the bites of potentially infected rodent fleas (for example, during a plague outbreak) or who have handled an animal known to be infected with the plague bacterium. Such experts also recommend that antibiotics be given if a person has had close exposure to a person with suspected plague.

Persons who must be present in an area where a plague outbreak is occurring can protect themselves for 2 to 3 weeks by taking antibiotics. The preferred antibiotics against plague are the tetracyclines or the sulfonamides." (CDC, 2004, ¶ 4). A plague vaccine is no longer available in the United States.

In conclusion, although our society and humankind has progressed greatly since the 14th century, the plague is still an ever-present threat. With biochemical terrorism in a biological warfare scenario, the plague bacillus could be delivered via contaminated vectors (fleas) causing the bubonic type or, more likely, via aerosol causing the pneumonic type -- almost 100% fatal.


Works Cited