L33 Cholera and bacillary dysentery Flashcards
Both cholera and bacillary dysentery are notifiable disease in HK. T/F?
True!
What are the 2 microorganisms causing bacillary dysentery?
- List some species/ strains of the 2 microorganisms.
- Shigella species
- Group A: S. dysenteriae - most pathogenic
- Group B: S. flexneri
- Group C: S. boydii
- Group D: S. sonnei - least pathogenic - Escherichia coli
- only certain stains
- O157:H7: EHEC/verotoxigenic Ecoli - Shiga- like toxin producing
- both toxigenic and hemorrhagic, found in GIT of cattle (hamburger meat)
- O104: H4: 2011 outbreak in Germany - sprouts
Causative agent cause cholera?
- This agent is classified based on O antigen, and only toxigenic strains of ______ and _______ cause pandemics.
Others cause self-limiting GE and wound infections
Vibrio cholerae
- O1 and O139
Describe how Vibrio cholerae reach and colonize the intestinal mucosa. (3)
- Fecal oral route
- Acid labile: survive gastric acid by large inoculum size (i.e. high infectious dose) and protection by food > antacids/PPI increase risk
- Attach to intestinal mucosa by pili
Describe how the Cholera toxin works.
- Binds to enterocyte surface receptors (Gs pathway)
> activate adenylate cyclase
> increase cAMP
> increase Cl- secretion into lumen with reduced Na reabsorption
> massive fluid/ e- loss
Which of the following about Virbio infection is incorrect?
A. It has an acute onset with an incubation period in hours - 5 days
B. Patients are mostly symptomatic with high fever
C. In severe cases, patients will have vomiting and rice-water stool (mucus), dehydration with hypovolemic shock and electrolyte imbalance
D. Death can result within 12 hours in serious cases
E. Stool sample is taken for microscopy and culture for investigations
B
- mostly asymptomatic and with no high fever
Treatment for Cholera (General, specific, public).
General:
- Fluid and electrolytes: ORS, IVF replacement
Specific:
- Doxycycline (abx): not necessary, reduce volume of diarrhea and Vibrio excretion
Public health:
- Contact tracing
How can Vibrio cholera be prevented? (2)
- Vaccines: 2 oral-killed vaccines
- poor efficacy, short duration
- for travelers going to endemic countries - WASH
- sustainable safe water, sanitation, hygiene
Why antibiotics are indicated in Shigella infection but not in Vibrio?
Shigella has a low infectivity dose = higher risk of spreading infection (heat-stable)
How does Shigella species colonize intestinal mucosa? (3)
- Fecal-oral route
- Acid-resistant: smaller inoculum size (low infectious dose: 10-100 bacteria
- Invade enterocytes and destroy intestinal mucosa by Shiga toxin, but rarely invade systemically
How does Shiga toxin work? (3)
- Binds to intestinal mucosa receptors >
inactivate ribosomes and protein synthesis >
cell death, vascular injury (blood and mucus in stool)
Which of the following about Shigella is correct?
A. Incubation period is within a week
B. 50-80% of patient has diarrhea with blood and mucus
C. Patient will have fever, abdominal pain and vomiting
D. Patient may have HUS
E. Stool culture is required while blood culture is rarely done
All of the above
Treatment for Shigella? (General, specific, public)
- Most cases self-limiting
1. Rehydration
2. Antibiotics (e.g. ampicillin) to reduce excretion and duration of symptoms
3. Contact tracing
Escherichia coli also causes bacillary dysentry. EHEC is one of the causative agents. Pathogenesis? (4)
Clinically: Traveller’s diarrhea
- **EHEC (enterohemorrhagic E.coli)
- bloody diarrhea by heat-labile toxin = Shiga-like toxin with a similar mechanism like Shigella: (1)
(- Binds to intestinal mucosa receptors >
inactivate ribosomes and protein synthesis >
cell death, vascular injury (blood and mucus in stool) )
ETEC (enterotoxigenic E.coli)
- watery diarrhea with a similar mechanism as V.cholerae
(- Binds to enterocyte surface receptors (Gs pathway)
> increase cAMP
> increase Cl- secretion into lumen with reduced Na reabsorption
> massive fluid/ e- loss)
Which of the following about Escherichia coli caused dysentery is correct?
A. It causes HUS in children
B. It causes hemorrhagic colitis in the elderly presented with bloody diarrhea
C. It causes watery diarrhea
D. It causes fever and vomiting
E. HUS in children is a triad of hemolytic anemia, thrombocytopenia, and AKI
All of the above
E: 3-5% mortality
