Other Yersinia are mentioned in enteric gram-negative bacilli section.
Causes plague
Produces V and W antigen
Virulence factor: V and W antigen, endotoxin, antiphagocytic capsule
Rat, ground squirrel, prairie dogs - common reservoirs
Transmitted by fleas, or ingestion of contaminated animal tissues, or by inhalation.
Transmission vector - fleas
Carried from inoculation site to regional lymph node lymphatically
-> Ingestion by phagocytes
-> Multiply within phagocytes
-> Released with new envelope
-> Increased resistance to phagocytosis
Haemorrhagic necrosis in affected lymph nodes
High concentration of PMN and extracellular bacteria in these nodes
Haematogenous spread to other sites.
Flea ingest blood from infected animal
-> Y. pestis produce coagulase - blood clot in flea foregut
-> Multiply within the foregut
-> Next attempt to feed - regurgitate from foregut
Incubation: 2 - 8 days
Sudden high fever, headache, myalgia, weakness -> prostration.
-> Then characteristic painful bubo develops
* Pronouced swelling with one or more infected lymph nodes
* Typically in the groin, occasionally in neck or axillae
-> Hypotension
-> Septic shock, death
May also have pustules/vesicles containing leukocytes and Y. pestis.
Mortality >50% if untreated
Patient overwhelmed by massive bacteremia before buboes develop.
* Highly contagious
Mortality almost 100% if untreated.
Transmission by aerosol inhalation.
Haematogenous dissemination to the meninges.
Bacteria demonstrated in CSF
Cause by direct handling or ingestion of contaminated tissue.
Stains bipolarly
Diagnosis can be made clinically, by culture, gram stain.
Culture on MacConkey or blood agar.
First line: gentamicin, doxycycline (tetracycline)
For plague meningitis - chloramphenicol
Formalin-killed vaccine available.
Efforts to minimise exposure to rodents and fleas.
Things to revise/add later:
Bibliography:
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