Transcript The Plague - Biol 448B: Fundamentals of Tropical Disease

The Plague
(insert screaming now)
Vaughn and Tess
February 4, 2008
4 Flavours of The Plague
Bubonic – Fever, buboes (very swollen, painful
lymph nodes that can form abscesses), 50-60%
mortality
 *Pneumonic – coughing, sputum, crackling,
dyspnea; near 100% mortality within 2-4 days
 *Septicaemic – Fever, GI symptoms (vomitting,
diarrhea, pain), purpura, petechiae in late stages;
75% mortality within a few days, quite rare
 Meningeal – Fever, same as meningitis; Very rare
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*Can be primary or secondary plague infection
Clinical Signs of Bubonic Plague
1.
Buboes – Painful, swollen lymph nodes
(axillary, inguinal, femoral or cervical)
- Can supparate.
Bacteria migrate to lymph nodes, resist destruction
by phagocytes and multiply rapidly leading to
necrosis and hemorrhage
Disease course
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Incubation of 1-7 days
Usually starts as bubonic plague, then
bacteria spread via lymph nodes through
blood (sepsis)
Patients die of pneumonic plague, or
septicaemic plague (multi-organ failure)
Necrosis and petechiae characteristic of
late stage disease.
Disease Source
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Yersinia pestis – rod shaped, gram neg. bacteria
Most are killed by neutrophils, but a few are
taken up by histiocytes which can not kill them.
Re-synthesize their capsule resist
phagocytosismultiply rapidly
Vectors
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Main vector – Oriental Rat Flea
(Xenopsylla cheopsis)
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Stomach becomes blocked from abundance of
bacteria. When the flea bites it’s next victim,
the bacteria are regurgitated into the blood.
Reservoirs
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Many wild rodents
Black rat (Rattus rattus) is the main culprit
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Lives in close proximity to humans (homes)
“Rat-fall” is common omen of an epidemic
Domesticated rodents and pets
Transmission
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Fleas live in nests of wild rodents
Disturbance (war, flood etc) cause wild
rodents to migrate to urban areas.
Infected fleas jump from wild rodents to
domesticated rodents, pets Humans
Direct infection from animals possible
Human-to-human transmission via
respiratory droplet (pneumonic plague)
Diagnosis
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Y. pestis is easily recovered from: blood
(septicaemic plague), aspirates of bulboes
(bubonic plague), sputum (pneumatic
plague) and differentiated in the lab
Capsular fraction 1 antigen basis of
serological tests
Note: Can be confused with Y.
psuedotuberculosis in labs with little or no
experience in dealing with it.
Management
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Requires prompt antibiotic treatment.
With pneumonic or septicemic plague,
must be administered within 1 day of
symptoms.
Treatment: Use 1 antibiotic; Streptomycin
preferred; gentamicin and tetracycline
group also effective
Course of treatment: at least 7-10 days
Resistance: Only 1 case of multi-drug
resistance found in Madagascar.
When given early, reduces mortality to 514%
Prevention
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Formol-killed vaccine once
available for health care workers
that conferred some immunity
against bubonic plague, but not
pneumonic plague
Mass immunization not in place
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Not practical as immunity too slow
to develop in the case of an
outbreak
Promise in new vaccines that are
under development
Y. pestis Epidemics
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Recorded since biblical times, many
epidemics throughout history
Examples:
1st epidemic (Antiqua) – 541 AD;
Mediterranean region, 50-60% of pop.
2nd epidemic (Medievalis) – 1346-1351; 1/3
of the pop. of Europe died (20-30 million)
3rd epidemic (Orientalis) – 1855-1890;
started in China, spread through Asia; 10
million died in India alone
The Black Death Epidemic
The Modern Day Situation
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Roughly 2000 cases and 200 deaths per year (WHO)
Vast majority in Africa
About 13 cases a year in the US
Anatomy of the Plague
Plague Control
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Isolation of patients
with pneumonic
plague
Flea and rodent
control
Start therapy if plague
is suspected – can
take too long to
confirm.
Plague as a Weapon
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Aerosolized bacteria  Pneumonic plague
Takes 48-72 hours to confirm diagnosis
50kg of Y. pestis could infect 150,000 and kill
36,000 in a city of 5 million in a worst-case
scenario.
Bacteria would remain viable in an aerosol for
1 hour for a distance of 10 km.
Discussion
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Would we be better off putting money
toward vaccines or emergency response
with regards to a bio-terrorist attack?
Why?