iv. The Black Plague (Yersinia Pestis) Flashcards
What type of bacteria is the Black Plague?
Gram negative bacteria
Microbial Pathogenesis: The 5 Challenges:
- Maintain a reservoir
- Gain access to new host
- Adherence
- Mechanisms of disease causation
- Exiting from one host, entering another or returning to reservoir
Microbial Pathogenesis: The 5 Challenges:
1. Maintain a reservoir:
- Maintain a reservoir: human, animal or environ source in which microbe can exist & can be transmitted - rodents (plague), contaminated animal products (leather, wool - anthrax) to human = ZOONOTIC infection (zoonosis) [Rodents, gerbils -> zoonosis]
Microbial Pathogenesis: The 5 Challenges:
- Gain access to new host:
- Gain access to new host: Portal of entry (skin, mucous membrane, resp tract, GIT); Mode of transmission (contact, traumatic/parenteral inoculation, vector-borne, inhalation, ingestion) - Vector = living creature that transmits infection from 1 host to another eg, mosquito, flea, tick [vector = flea; entry via inoculation due to vector bite]
Microbial Pathogenesis: The 5 Challenges:
- Mechanisms of disease causation:
- Mechanisms of disease causation: adherence, invasion (agressins), toxins (exo/endo), immunologically-mediated damage (cytokines, superantigens, hypersensitivity-mediated rxns) [evade host defence - Fraction 1 Ag, low calcium response plasmid, V & W antigens, intracellular survival; invasion of tissues (buboes, lungs etc.); toxins (exotoxin - murine exotoxin;
endotoxin [LPS]; immunological damage (inflamm cytokines)]
Microbial Pathogenesis: The 5 Challenges:
- Exiting from one host, entering another or returning to reservoir:
[Human-human; animal-human; flea to animal/human returning to reservoir (rodents)]
History of Plague:
3 documented pandemics in recent history: (3)
- 6th century (541-75 AD) - Justinian plague
- 14th century (1347-17th C AD)
- 1860 (China) -> 1894 (Hong Kong) -> SE Asia, India, Africa & Americas
Yersinia Pestis as an agent of bioterrorism:
Historically =
Long history as bio-weapon, ancient china used infected animal carcasses to contaminate enemy water supply
Yersinia Pestis as an agent of bioterrorism:
1346/7:
Genoese possession of Caffa (trade emporium on Crimean peninsula) - now Feodosiya, Ukrainian. Mongolian army withering from plague & their general catapulted infected human corpses over city wall - Genoese traders fled, transferring plague via ships into S. Europe
Yersinia Pestis as an agent of bioterrorism:
WW2:
WW2: Japanese army weaponised plague by breeding & releasing infected flees into Manchuria & performing dissection &/or vivisection on victims
Yersinia Pestis as an agent of bioterrorism:
Post WW2:
Post WW2: both US & USSR had significant bio-weaponisation programs using plague
Yersinia Pestis as an agent of bioterrorism:
Today:
Today, Y. Pestis is classified as category A agent for possible bioterrorism attacks (aerosolised pneumonic plague = most significant threat)
Bacteriology & Properties: (2)
- Gram -ve bacillus.
- Obligate pathogen (cant survive freely in environment), unable to replicate in nature outside host (flea/mammal), survive drying for few days, survival prolonged in
dried blood & secretions.
The Plague Cycle: Zoonosis:
Pathogenesis:
Virulence factors: (3)
- Temp-dependant coagulase (<30 degrees); Fraction 1 antigen (capsular glycoprotein - 37 degrees), low calcium response at 37 deg mediated
- By 70 kb plasmid is important for adaptation to IC environ; V & W antigens (maintain bacteriostasis & aid IC survival); Yersinia OMPs (Yops)
- Type E & K important for virulence; Other - antigen 4 or pH 6 antigen; pigment production; LPS endotoxin; plasmid-encoded murine exotoxin
(Lethal only to mice & rats)
Pathogenesis:
Fleas are ____ blooded -> ingestion of organism from blood of suitable reservoir result in clotting of flood in flea’s ________ (foregut) -> blood containing many organisms regurgitated during subsequence feeding attempts -> perpetuation of infection cycle -> F1 Ag enables organism to evade _______ when produced at 37 deg -> immune evasion -> Intracellular survival negotiated by ‘low calcium response’ and V & W Ags
cold
proventriculus
phagocytosis
What are the plague syndromes? (4)
Bubonic
Septicaemic
Pneumonic
Uncommon
Plague Syndromes:
Bubonic:
Fever, painful lymphadenopathy (bubo)
Plague Syndromes:
Septicaemic:
Septicaemic: Bacteraemia often occurs in bubonic plague (40% of cases). Severe illness: fever, rapid shock & death w/in days
Plague Syndromes:
Pneumonic:
Pneumonic: primary or secondary to bacteraemia spread in bubonic/septicaemic plague. Cough, bloody vomit, ± bubo (depending on primary or secondary)
Plague Syndromes:
Uncommon: (2)
Uncommon:
- Pharyngeal: painful, inflames pharynx, local lymphadenopathy
- Meningitis: fever, nuchal rigidity, usually with bubo
How do you diagnose the Black Plague? (3)
- Bubo aspirates; blood cultures; sputum (? Pneumonic); CSF (? Meningeal)
- Microscopy (Wayson, Giemsa/Gram stains); culture
- Serology or PCR
What is the treatment for the Black Plague? (4)
- Untreated, case fatality rate > 50%
- Antibiotics eg. Aminoglycosides; doxycycline; fluoroquinolones
- Supportive therapy
- Infection prevention & control (as appropriate)
What is the prevention for the Black Plague?
Surveillance, public education, rodent & flea control, chemoprophylaxis for close contact with plague pneumonia & indv exposed in lab accidents; infection prevention & control
