The causative organism is Yersinia pestis, and the vector is the flea transmitting it from animals to humans.
About
- Yersinia pestis is a Gram-negative enterobacteriaceae.
- Bubonic is one form with a large bubo in the groin.
- Organism was first detected by Alexander Yersin.
Characteristics
- Gram-negative, rod-shaped bacillus, facultative intracellular and facultative anaerobe.
- Looks like a safety pin, allowing for rapid diagnosis.
Source
-
The flea is the main vector that takes a blood meal from a rodent infected with Yersinia pestis. Bacteria agglutinate and block the flea’s upper intestinal tract, replicate, and are regurgitated into the next host. Humans become infected if fleas bite them after infesting domestic rats.
- Spread can also occur human-to-human via aerosols from individuals with pneumonic plague.
- Yersinia pestis can be used in warfare and dispersed through aerosol transmission.
Virulence
-
The cell membrane contains lipopolysaccharide, a highly toxic compound that forms the basis of endotoxin.
-
When bacterial cells are broken down by the immune system or antibiotics, lipid A fragments from the cell membrane enter the bloodstream, releasing endotoxin.
-
This can trigger a dangerous chain of events known as sepsis syndrome.
- Yersinia pestis exhibits short bipolar staining with Giemsa and has 3 plasmids contributing to its virulence:
- F1 capsular protein prevents phagocytosis.
- Outer membrane protein and type III secretion system enhance virulence.
- It also produces a plasminogen activator to aid in the spread of infection.
Clinical/Pathogenicity
-
Bubonic plague affects mammalian lymph nodes, with symptoms such as fever, malaise, headache, and severe systemic responses. Inguinal nodes are commonly affected. Symptoms include hypotension, tachycardia, splenomegaly, and hemorrhagic buboes.
-
Septicemic plague is a more severe form, with fewer buboes. It leads to sepsis, nausea, vomiting, abdominal pain, and diarrhea. Symptoms may include multi-organ failure, DIC, renal failure, shock, and ARDS. Mortality is high.
-
Pneumonic plague causes fever, malaise, chest discomfort, and pneumonia, progressing to bloody sputum, respiratory failure, and death if untreated.
Investigations
- FBC, U&E, LFTs, CXR, Blood cultures.
-
Aspirate from buboes, sputum, or buffy coat can be stained and cultured, with methylene blue showing the characteristic bipolar staining organism.
-
Bipolar coccobacilli appear in smears after staining with Wayson’s stain or by immunofluorescence.
- Seroconversion or a single anti-F1 antibody titer > 128 confirms the diagnosis.
- PCR can also be used.
Management
- ABC, isolation, and strict precautions (gowns, masks, gloves) are necessary for at least 48 hours in cases of pneumonic plague.
-
Antibiotics such as Streptomycin (1 g IM q12h) or Gentamicin (5 mg/kg/day) are first-line treatments. Alternatives include Ciprofloxacin, Tetracycline, and Chloramphenicol.
- Manage complications such as DIC, respiratory failure, and circulatory failure supportively.
- Vaccination offers limited protection, especially against the pneumonic form.
- Notifiable disease.
References