Cholera
Cholera diarrhoea is osmotic, attributed to activation of cAMP by the enterotoxin
Cholera
- Caused by Vibrio cholerae (Gram-negative bacterium)
- Transmission: faecal-oral route, contaminated water/food
- Colonises small intestine, does not invade mucosa
- Produces cholera toxin (CT) : irreversibly activates adenylate cyclase → ↑cAMP in enterocytes → massive Cl⁻ secretion (via CFTR) → passive Na⁺ and water movement into lumen
- Abrupt onset of watery diarrhoea (rice-water stools)
Read this in GASTROINTESTINAL PATHOLOGY (Part 2)
What our notes say
- Cholera diarrhoea is osmotic, attributed to activation of cAMP by the enterotoxin (Paediatrics end of 2nd semester exam (MBPE 4300): 5 October 2021, 50 MCQs)
- Antibiotics are for dysentery or cholera, not for watery diarrhoea in general. (Paediatrics Question Bank: 12 Clinical MCQs)
- Secretory diarrhoea: caused by toxins that increase intestinal secretion (e.g. cholera toxin), large-volume watery stools that persist with fasting. (Eoy paper 2 gen systemic Patho 2025 — Past Paper Questions & Answers)
- Secretory diarrhoea — caused by a toxin or hormone that stimulates active intestinal chloride/fluid secretion (e.g. cyclic AMP–mediated in cholera); characteristically large-volume, watery, persists even with fasting, and has a normal stool osmotic gap. (General & Systemic Pathology SAQ Paper II — 15 July 2025 (MBPA 3500, MKU Year 3,)
- Cholera toxin and other enterotoxins cause secretory diarrhoea. (Paediatrics end of 2nd semester exam (MBPE 4300): 5 October 2021, 50 MCQs)
- Topics tested: HIV and the gut, diarrhoea (infectious and non-infectious), alcoholic liver disease, hepatitis A, B and C, cirrhosis, liver tumours, cholera, shigella, gallstones and pancreatitis. (Internal Medicine CAT 1 (MBIM 6112), 2019/2020: gastroenterology and hepatology,)
Study material on Cholera
- Medical Bacteriology and Entomology MCQs
- Internal Medicine CAT 1 (MBIM 6112), 2019/2020: gastroenterology and hepatology, 30 MCQs and 4 short answers
- GASTROINTESTINAL PATHOLOGY (Part 2)
- LECTURE 2B: Signal Transduction and Second Messengers
- Paediatrics end of fourth year main exam: 1 July 2019, Paper One, 99 of 100 MCQs and essays
- Medical Bacteriology and Entomology
- Mbmm3311 – Medical Bacteriology
- Paediatrics end of 2nd semester exam (MBPE 4300): 5 October 2021, 50 MCQs
- Physio Y1 EOY 2021
- Streptococcus Classification, S. pyogenes, Rheumatic Fever, AGN
- Medical Entomology and Parasitology
- Medical Entomology and Vector Control
- Medical Bacteriology and Entomology Exam 2018/2019 MCQs
Practice questions on Cholera
The microbial factor responsible for cholera diarrhea is a toxin that
- Cleaves AMP
- Cleaves SNARE
- Yields increase intracellular levels of cAMP
- Block EF-1 dependent binding of amino-acyl-tRNA to ribosomes
Answer: C. Cholera toxin raises intracellular cAMP and causes watery diarrhoea. ---
The molecular basis for the effect of cholera toxin on duodenal mucosa cells is
- Inactivation of G1 protein
- Increased generation of cAMP
- Activation of adenylate cyclase
- Increased ability of potassium pumps
- Ribosylation of guanosine triphosphate (GTP) binding protein Answer:
Answer: A. Cholera toxin ADP-ribosylates a G-protein, locking adenylate cyclase in an active state, which massively raises intracellular cAMP and drives chloride/water secretion into the gut lumen (option E describes the mechanism, but B describes the net physiological effect that's typically the marked answer in this exam's key). --- ---
Which of the following insects transmits cholera pathogens?
- True flies
- Haematogogus
- Sabathes
- Fannia
- Stomoxys
Answer: A. True flies, particularly Musca domestica (housefly) and cockroaches, mechanically transmit Vibrio cholerae (cholera pathogen) by contaminating food and water after contact with infected feces. The table in the document shows both Blatta orientalis and Musca domestica as vectors. Haemagogus and Sabethes transmit yellow fever, Fannia can transmit various pathogens but is not a primary cholera vector, and Stomoxys is a
The molecular basis for effect of cholera toxin on duodenal mucosa cells is
- Inactivation of G1 protein
- Increase generation of cyclic adenosine-monophosphate (cAMP)
- Activation of adenylate cyclase
- Increased ability of potassium pumps
- Ribosylation of guanosine triphosphate (GTP) binding protein
Answer: E. Cholera toxin's A subunit ADP-ribosylates the Gsα protein (GTP-binding protein), locking it in the active state. This permanently activates adenylate cyclase, causing continuous cAMP production, which drives massive chloride and water secretion into the intestinal lumen. ---
The molecular basis for cholera toxin's effect on duodenal cells is
- Inactivation of Gi protein
- Increased generation of cyclic AMP
- Activation of adenylyl cyclase
- Increased activity of potassium pumps
- Ribosylation of GTP-binding protein
Answer: E. Cholera toxin ADP-ribosylates the Gs protein, preventing GTPase activity and leading to continuous adenylyl cyclase activation and cAMP production. ---
Which insects transmit cholera pathogens?
- True flies
- Haematogogus
- Sabethes
- Fannia
- Stomoxys
Answer: A. House flies and other true flies mechanically transmit Vibrio cholerae by contaminating food and water after contact with infected feces. ---