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Bubonic Plague
By Prayas Patel
Outline
1. General information
2. Etiological agent and vector
3. Transmission
4. Human plague infections
Plague
1.Caused by Yersinia pestis.
2.Bacteria transmitted by:
• Bites from fleas (usually
Xenopsylla cheopis)
• Handling an infected animal
(rarely)
History
Pandemic of the mid-14th century
was just 1 of 3 pandemics of the
plague thus far (Kosoy 2004).
US and Global Incidence
1. Plague has not been eradicated.
2. Cases globally: 1,000 – 2,000 a
year
3. Cases in US.: 10 – 15 a year
Figure 1. Reported cases of human plague by counties in the
US between the years 1970-1997 produced by the CDC.
Figure 2. Countries with reported human plague infections between the years
1970-1998 and the distribution of animals infected with the plague bacterium
around the world produced by the CDC.
Outline
1. General information
2. Etiological agent and vector
3. Transmission
4. Human plague infections
Etiology
Yersinia pestis
1. Classified in the family
Enterobacteriaceae.
2. Evolved from a clone of Yersinia
pseudotuberculosis (Achtman
14047).
Yersinia pestis
1.Coccobacillus
2.Gram-negative
3.Facultative anaerobe
Biovars
Y. pestis has 3 biovars
(Achtman et al. 1999)
Biovar – “a strain of a strain”
3 Biovars (Perry 1997)
• Antigua – 6th century
• Medievalis – 14th century
• Orientalis – 20th/21st century
Virulence
Virulence factors
• Biofilms (Darby 2008)
• Interference of inflammatory
response (Sun et al. 2007)
• Induce immunodeficiency (Bi
et al. 2008)
Reservoirs
1. Most common reservoirs are wild
rodents.
2. These would include
Rattus species
Rock squirrel
• California ground squirrel
•
•
3. EVEN the soil
(Infectious Disease Society of
America)
Xenopsylla cheopis
Figure 3. A Xenopsylla cheopis.
X. cheopis
1. Ectoparasite
2. Found worldwide with a host
(typically a species of Rattus).
•Most commonly in tropical and
subtropical climates.
X. cheopis feeding
1. X. cheopis feeds from the blood
vessel of its host.
• Injects salvia to prevent clotting
(Andersen et al. 2007).
2. Proventriculus is a valve-like organ
between esophagus and stomach.
3. Both sexes can transmit infection.
Y. pestis’ impact on flea


Bacteria may occasionally block the
flea’s digestive tract.

Blockage is caused by biofilms
(Perry 1997).

Process aids in spread of disease.
Y. pestis’ impact on flea


To feed again, the flea must remove
the blockage.

By removing the blockage the flea
may inadvertently spread the
infection.
Outline
1. General information
2. Etiological agent and vector
3. Transmission
4. Human plague infections
Transmission
1. Bites from infected fleas
2. The bacterium can enter
through breaks in the skin.
Transmission (continued)
1. Contact with plague infected
animal’s carcass.
2. Plague may be spread through
the air by an animal with
pneumonic plague.
Figure 5. The various cycles the bubonic plague circulates in and the modes of
transmission between organisms with the infection.
Humans as “hosts”


Humans are NOT the primary
host of Y. pestis.

They are INCIDENTAL hosts
(Infectious Disease Society of America
2009).
Human bubonic plague
Bubonic plague occurrence in
humans is related to: (Infectious Disease
Society of America 2009)


Percentage of hosts killed by infection

Amount of human exposure to rodents
Human to Human
Transmission


Found ONLY in pneumonic
plague.

Droplets expelled may contain
bacteria.
Outline
1.General information
2.Etiological agent and vector
3.Transmission
4.Human plague infections
Disease Progression


The bacteria enters into the
body

Bacteria spreads to lymph
tissue

The bacteria may also spread
to infect the lungs (pneumonic
plague).
Signs and Symptoms
• Fever, chills, headache
• Painful, warm, and swollen
lymph node
Called a bubo (Bubonic plague)
• Death caused by endotoxic
shock.
Bubo
Figure 6. A bubo on the thigh of a person infected with Y. pestis.
Treatment
1. The best courses of treatment
are the antibiotics Gentamicin or
Streptomycin.
2. Vaccines were developed but
were ineffective.
Review
1. General information
2. Etiological agent and vector
3. Transmission
4. Human plague infections
Literature Cited
Achtman, M., K. Zurth, G. Morelli, G. Torrea, A. Guiyoule, and E.
Carniel. 1999. Yersinia pestis, the cause of plague, is a recently
emerged clone of Yersinia pseudotuberculosis. Proceedings of
the National Academy of Sciences of the United States of
America 96:14043-14048.
Andersen, J. F., B. J. Hinnebusch, D. A. Lucas, T. P. Conrads, T. D.
Veenstra, V. M. Pham, and J. M. Ribeiro. 2007. An insight into
the sialome of the oriental rat flea Xenopsylla cheopis. BMC
Genomics 8:102-110.
Bi, Y., Z. Du, Y. Han, Z. Guo, Y. Tan, Z. Zhu, and R. Yang. 2008.
Yersinia pestis and host macrophages: immunodeficiency of
mouse macrophage induced by YscW. Journal of the British
Society for Immunology 126:141-153.
Center for Disease Control. 2007. Plague. Accessed online at
http://www.cdc.gov/ncidod/dvbid/plague/index.htm.
Darby, C. 2008. Uniquely insidious: Yersinia pestis biofilms. Trends in
Microbiology 16:158-164.
Literature Cited (continued)
Infectious Disease Society of America. 2009. Plague: Current,
comprehensive information on pathogenesis, microbiology,
epidemiology, diagnosis, and treatment. Accessed online at
http://www.cidrap.umn.edu/idsa/bt/plague/biofacts/plaguefactshe
et.html
Kosoy, M. K. and K. L. Gage. 2004. Natural history of plague:
perspectives from more than a century of research. Annual
Review of Entomology 50:505-528.
Perry, R. D. and J. D. Fetherston. 1997. Yersinia pestis – Etiologic
agent of plague. Clinical Microbiology Review 10:35-66.
Sun, P., J. E. Tropea, B. P. Austin, S. Cherry, and D. S. Waugh. 2007.
Structural characterization of the Yersinia pestis Type III
secretion system needle protein YscF in complex with its
heterodimeric chaperone YscE/YscG. Journal of Molecular
Biology 377:819-830.