Animal- and arthropod-transmitteddiseases

Dec 6, 2006Ch. 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 plaguebacterium

• Antibiotics are effective against plague,but if an infected person is not treatedpromptly, the disease is likely to causeillness or death

Epidemiology

• Wild rodents incertain areas areinfected with plague

• Outbreaks usuallyassociated withinfected rats and ratfleas (Xenopsyllacheopis)

• Globally, the WHOreports 1,000 to 3,000cases of plague eachyear

http://www.cdc.gov/ncidod/dvbid/plague

History of plague

• First pandemicspread from Egyptto Europe, Africa,and Asia 542-600

• Second pandemicknown as the BlackDeath spread fromAsia to Europe inthe 1300s

http://bubonicplague.quickseek.com/

Natural history• Epidemics usually involve

rats• Last rat-borne epidemic in

the US occurred in LosAngeles in 1924-25

• Since then, all human casesin the U.S. have beensporadic cases acquiredfrom wild rodents

• Rock squirrels and theirfleas are the mostfrequent sources of humaninfection in thesouthwestern states www.mammalogy.org

Courtesy of Diliff.

Geographic distribution

• Averages about 18cases per year in US

• Mostly in people < 20years of age

• About 1 in 7 personswill die

• Epidemic plague occursAfrica, Asia, & SouthAmerica associatedwith domestic rats

Forms of disease• Bubonic plague

– enlarged, tender lymph nodes,fever, chills and prostration

• Septicemic plague– fever, chills, prostration,

abdominal pain, shock andbleeding into skin and otherorgans

• Pneumonic plague– fever, chills, cough and

difficulty breathing; rapidshock and death if not treatedearly 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 severeillness, called plague septicemia

• Progression leads to lung infection orplague pneumonia

• Incubation period of primary pneumonicplague 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 plagueis made, the patient should be isolated, andlocal and state health departments shouldbe notified

• The drugs of choice are streptomycin orgentamicin, but a number of otherantibiotics are also effective

• Those individuals closely associated withthe patient, particularly in cases withpneumonia, should be traced, identified,and evaluated

Prevention• Epidemic plague is best prevented by

controlling rat populations in bothurban and rural areas

• In regions where plague is widespreadin wild rodents, the greatest threat isto people living, working, or playing inareas 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 DNA-DNA hybridization member of theEnterobacteriaceae family

• 11 named species, but only 3 arehuman pathogens– Y. pestis, the etiologic agent of plague– Y. pseudotuberculosis and Y.

enterocolitica

http://www.cdc.gov/ncidod/dvbid/plague

Zhou et al. Microbes Infect 6:1226-34, 2004.

Diagram removed due to copyright restrictions.

Invasion

• EnteropathogenicYersinia speciesinvade culturedmammalian cells

• Mediated by invgene productinvasin

• Outer membraneprotein binds β1integrins

Isberg and Barnes, J Cell Sci 114:21-28, 2001.

Figure by MIT OCW.

Bacterium Bacterium Bacterium

No Signaling

Signaling

Signaling

Invasin

Integrin

D2

A. Low substrate density B. High substrate density C. Substrate dimerization

Neutra et al. Nature Immunol 2:1004-9, 2001.

Image removed due to copyright restrictions.

Hu et al. J Bacteriol 180:5192-5202, 1998

rep region

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Figure by MIT OCW.

Jarrett et al. J Infect Dis 190:783-92, 2004.

Images removed due to copyright restrictions.

Hu et al. J Bacteriol 180:5192-5202, 1998

Image removed due to copyright restrictions.

Cornelis Nature Rev Mol Cell Biol 3:742-754, 2002

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).