Makindo Medical Notes.com

The causative organism is yersinia pestis and the vector is the flea transmitting it from animals to humans.

About

• Yersinia pestis is Gram negative enterobacteriaceae
• Bubonic is one form with a large bubo in the groin
• Organism first detected by Alexander Yersin

Characteristics

• Gram negative rod-shaped bacillus facultative intracellular facultative anaerobe
• Looks like a safety pin so can rapidly diagnose

Source

• Flea is main vector that takes a blood meal from a rodent which contains Yersinia pestis. Bacteria agglutinate and block the fleas upper intestinal tract and replicate. Flea regurgitates the bacteria into the next host it feeds on. Humans become infected if the fleas infest domestic rats and the fleas bite humans.
• Spread can also be human to human with infected aerosol from an affected individual with pneumonic plague
• Can be used in warfare and dispersed by aerosol transmission

Virulence

• The cell membrane contains a special compound known as lipopolysaccharide which is extremely toxic to humans and forms the basis of endotoxin.
• The breakdown of bacterial cells by our immune system, or by antibiotics, fragments of the cell membrane containing lipid A are released into the bloodstream, releasing endotoxin.
• This can trigger a deadly cascade of events known as the sepsis syndrome
• Short bipolar staining with Giemsa and has 3 plasmids which convey its virulence
• F1 capsular protein which prevents phagocytosis
• Outer membrane protein and type III secretion system which enhances virulence
• Also produces a plasminogen activator which enhances spread.

Clinical/Pathogenicity

• Bubonic plague - has an affinity for mammalian lymph nodes. Associated with fever, malaise headache and severe systemic symptoms. Inguinal nodes affected most commonly. The patient becomes hypotensive and tachycardic. There is splenomegaly. Buboes may enlarge which become haemorrhagic.
• Septicaemic plague - a more fulminant form of bubonic plague in which buboes are less marked and sepsis proceeds with nausea, vomiting, abdominal pain and diarrhoea. There is a multiorgan failure with DIC, renal failure and shock. The patient may develop ARDS. Mortality is high.
• Pneumonia plague - causes fever, malaise and chest discomfort and mucoid pneumonia with then bloody sputum. Can rapidly lead to respiratory failure and death

Investigations

• FBC,U&E, LFTs, CXR, Blood cultures
• Stain aspirate of buboes or sputum or the buffy coat of blood with microscopy and culture with methylene blue shows the characteristic bipolar staining organism.
• Characteristic bipolar coccobacilli are seen in smears of these fluids after staining with Wayson’s stain or by immunofluorescence.
• Seroconversion or a single anti-F1 antibody titre > 128 confirms the diagnosis.
• PCR may also be used

Management

• ABC, Isolate. Organism alive and potent and lethal even up to three days in a dead body. Isolation of all patient as the pneumonic disease spreads via droplets for at least the first 48 hours with gowns, masks and gloves. Give Doxycycline or Ciprofloxacin to contacts.
• Antibiotics e.g. Streptomycin 1 g 12 hourly or Gentamicin 5 mg/kg/day is the drug of choice. Ciprofloxacin has also been used. Tetracycline and chloramphenicol are alternatives.
• Supportive management of DIC, Respiratory failure, Circulatory failure
• Vaccination is possible but has limited protection to pneumonic form
• Notifiable disease

References

• PERRY AND FETHERSTON. Yersinia pestis-Etiologic Agent of Plague