Yersinia Pestis Flashcards
General Characteristics of Yersinia Pestis?
Non-motile.
Non-spore forming.
Facultative intracellular pathogen.
One serotype:
3 biovars- Antiqua, Medievalis & Orientalis.
(A biovar is a group of microorganisms that share a genetic identity but have different biochemical or physiological characteristics)
Facultative Anaerobe.
Pleomorphic Gram -ve bacillus.
Classic Rodent Zoonosis.
Plague bacillus.
Important to note: Cause of Bubonic plague, Rodent borne, Flea bite transmission.
Staining method?
Stain used:
Wrights= Exhibits bipolar staining with Giemsa.
Wayson Staining= Saftey Pin Appearance.
Additional info about Giemsa:
Giemsa is the most commonly used stain for staining blood films for malaria diagnosis
Giemsa is made of eosin and methylene blue.
The eosin stains the parasite nucleus red, while the methylene blue stains the cytoplasm blue.
Giemsa induces a purple coloration of chromatin DNA, which contrasts with the blue-stained RNA-containing cytoplasm and nucleoli.
Epidemiology (Nice to know fact)
3 Historical plagues-
Justinian (541AD), Black Death (1334), Modern Plague (1860s).
Classified as: Re-emerging disease.
Endemic in: Many countries in Africa, USSR, Americas, Parts of Asia.
Carriers & Methods of Transmission?
Wild rodents (Rats & Squirrels)- Vectors Xenopyslla cheopis & brasiliensis.
Fleas (via feeding blood of infected animals)- normally a method of transmission to humans.
Human flea= Pulex irritans.
(1) Flea bites.
(2) Aerosols.
(3) Contact with secretions.
Virulence Factors:
Capsule = Antiphagocytic.
Somatic antigen complex-
*Contains somatic antigens including V &W.
*Enables bacteria to resist phagocytosis.
LPS- endotoxin activity
Ability to absorb iron.
Fibrinolysis enables the bacteria to spread in tissues.
Clinical Implications:
Causative agent of Plague/Black death
Types of plague:
(1) Bubonic
(2) Septicaemic
(3)Pneumonic
About the 3 Plagues?
Bubonic: 2-6 days of contact with organism for symptoms to appear.
Fever, headache, Chills, Swollen extremely tender lymph nodes (buboes)- in Inguinal & Femoral Regions.
GI Symptoms: Nausea, Vomiting, Diarrhea.
Bacteremia/Secondar Plague Septicemia. 40-60% Mortality rate- untreated
Septicaemic Plague:
Primary- +ve blood cultures but no palpable lymphadenopathy.
Secondary- Complication of both bubonic & pneumonic plague
Symptoms: Fever, Chills, Headache, Malaise, GI disturbances.
30-50% mortality rate (without treatment 100%)
Lab Diagnosis:
Gram stain- Gram -ve cocobacilli.
Culture:
(1) BA, MacCockney, Yersinia Selective Medium
(CIN= Cefsulodin-Irgasan-Novobiocin)
(2) Incubate at 35-37 degrees Celsius.
Lab investigations
Specimen:
Blood.
Bubo aspirates.
Sputum.
CSF.
Scraping from skin lesion.
*Minimise risk of creation of aerosols. Highly infectious Pathogen.
Colonial Morphology:
BA: Small shiny non-hemolytic colonies.
MAC: Very small translucent pink colonies.
Lab Diagnosis:
Biochemical tests:
Catalase +ve.
Oxidase -ve.
Fluorescent Antibody Test
Rapid Immunoassays
PCR
Treatment, Prevention & Control:
Early treatment, survival rate- 100%
Supportive Care.
Streptomycin/Gentamicin.
Tetracycline.
Chloramphenicol.
Prophylaxis:
Sulphonamides.
Tetracycline.
Prevention:
Control of Rat & Flea populations.
Control of infection from patients:
Isolation & Containment.
Handling of patients with care.
