Animal- and arthropod-transmitted
diseases
Dec 6, 2006
Ch. 27
Galán and Wolf-Watz review
Plague
• Infectious disease of animals and humans
• Caused by a bacterium named Yersinia
pestis
• People usually get plague from being bitten
by a rodent flea that is carrying the plague
bacterium
• Antibiotics are effective against plague,
but if an infected person is not treated
promptly, the disease is likely to cause
illness or death
Epidemiology
• Wild rodents in
certain areas are
infected with plague
• Outbreaks usually
associated with
infected rats and rat
fleas (Xenopsylla
cheopis)
• Globally, the WHO
reports 1,000 to 3,000
cases of plague each
year
http://www.cdc.gov/ncidod/dvbid/plague
History of plague
• First pandemic
spread from Egypt
to Europe, Africa,
and Asia 542-600
• Second pandemic
known as the Black
Death spread from
Asia to Europe in
the 1300s
http://bubonicplague.quickseek.com/
Natural history
• Epidemics usually involve
rats
• Last rat-borne epidemic in
the US occurred in Los
Angeles in 1924-25
• Since then, all human cases
in the U.S. have been
sporadic cases acquired
from wild rodents
• Rock squirrels and their
fleas are the most
frequent sources of human
infection in the
southwestern states
Courtesy of Diliff.
www.mammalogy.org
Geographic distribution
• Averages about 18
cases per year in US
• Mostly in people < 20
years of age
• About 1 in 7 persons
will die
• Epidemic plague occurs
Africa, Asia, & South
America associated
with domestic rats
Forms of disease
• Bubonic plague
– enlarged, tender lymph nodes,
fever, chills and prostration
• Septicemic plague
– fever, chills, prostration,
abdominal pain, shock and
bleeding into skin and other
organs
• Pneumonic plague
– fever, chills, cough and
difficulty breathing; rapid
shock and death if not treated
early
www.cdc.gov/ncidod/dvbid/plague
Diagnosis of plague
• Painful, swollen lymph node, called a bubo
• Onset usually 2-6 days after exposure
• Disease progresses rapidly and bacteria
invade the bloodstream, producing severe
illness, called plague septicemia
• Progression leads to lung infection or
plague pneumonia
• Incubation period of primary pneumonic
plague is 1-3 days
– Characterized by overwhelming pneumonia with
high fever, cough, bloody sputum, and chills
– Mortality rate > 50%
Treatment
• As soon as a diagnosis of suspected plague
is made, the patient should be isolated, and
local and state health departments should
be notified
• The drugs of choice are streptomycin or
gentamicin, but a number of other
antibiotics are also effective
• Those individuals closely associated with
the patient, particularly in cases with
pneumonia, should be traced, identified,
and evaluated
Prevention
• Epidemic plague is best prevented by
controlling rat populations in both
urban and rural areas
• In regions where plague is widespread
in wild rodents, the greatest threat is
to people living, working, or playing in
areas where the infection is active
– Eliminate food and shelter for rodents
– Surveillance in wild rodent populations
– Use of appropriate insecticides to kill
fleas
The bacterium
• Gram negative facultative anaerobe
• Formerly classified in the family
Pasteurellaceae, but based on DNADNA hybridization member of the
Enterobacteriaceae family
• 11 named species, but only 3 are
human pathogens
– Y. pestis, the etiologic agent of plague
– Y. pseudotuberculosis and Y.
enterocolitica
http://www.cdc.gov/ncidod/dvbid/plague
Diagram removed due to copyright restrictions.
Zhou et al. Microbes Infect 6:1226-34, 2004.
Invasion
• Enteropathogenic
Yersinia species
invade cultured
mammalian cells
• Mediated by inv
gene product
invasin
• Outer membrane
protein binds β1
integrins
Bacterium
Bacterium
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Integrin
No Signaling
Signaling
Signaling
A. Low substrate density
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C. Substrate dimerization
Figure by MIT OCW.
Isberg and Barnes, J Cell Sci 114:21-28, 2001.
Image removed due to copyright restrictions.
Neutra et al. Nature Immunol 2:1004-9, 2001.
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Figure by MIT OCW.
Images removed due to copyright restrictions.
Jarrett et al. J Infect Dis 190:783-92, 2004.
Image removed due to copyright restrictions.
Hu et al. J Bacteriol 180:5192-5202, 1998
Images removed due to copyright restrictions.
Figures 1 and 2 in "THE YERSINIA YSC–YOP 'TYPE III' WEAPONRY," Nature Reviews Molecular Cell Biology 3, 742-754 (2002).
Cornelis Nature Rev Mol Cell Biol 3:742-754, 2002