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 in 1348, to spread across Europe, taking with it,
one-third of its population. We call it the bubonic plague though in the
nineteenth century, historians named it the Black Death named 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 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
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
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
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
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
Diagnosis 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
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 Streptomycin. Incision and drainage of
buboes may be necessary. Material drained from the buboes 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
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.
Cantor, N. F. (2002). In the wake of the plague. New York, NY:
CDC (2005), Division of vector-borne infectious diseases.
February 7, 2005. http://www.cdc.gov/ncidod/dvbid/plague/epi.htm.
Herlihy, D. (1997). The black death and the transformation of the
West. Cambridge, MA: Harvard University Press.
Knox, E. L. (1995). The Black Death.
February 8, 2005. http://www.idbsu.edu/westciv/plague.
Minnaganti, V.R. & Cunha, B.A. (2003). Plague.
February 7, 2005, http://www.emedicine.com/med/topic3381.htm.
Velendzas, D. & Dufel, S. (2004). CBRNE – Plague.
February 7, 2005, http://www.emedicine.com/EMEERG/topic428.htm.
Copyright © 2005 Lori M. Netahlo-Barrett
Written by Lori M. Netahlo-Barrett. If you have questions or comments on
this article, please contact Lori M. Netahlo-Barrett at:
Published online: 04/10/2005.