Profuse watery diarrhea (“rice water stools”), leading to dramatic fluid loss, severe dehydration, and hypotension that frequently leads to death, is the hallmark of which toxin activity?
a. Cholera toxin b. Enteric endotoxin c. Shiga toxin d. Toxin A
The correct answer and explanation is:
Correct Answer: a. Cholera toxin
Explanation:
The hallmark of profuse watery diarrhea, often described as “rice water stools,” is most commonly associated with the activity of cholera toxin, which is produced by the bacterium Vibrio cholerae. Cholera toxin is an enterotoxin that disrupts the normal absorption and secretion processes in the intestines, leading to severe fluid loss.
Mechanism of Action:
Cholera toxin consists of two subunits:
- The A subunit, which is enzymatically active.
- The B subunit, which binds to the GM1 ganglioside receptor on intestinal epithelial cells.
Once the toxin binds to the intestinal lining, the A subunit is internalized and activates the enzyme adenylate cyclase via ADP-ribosylation of the Gsα protein. This causes a dramatic increase in intracellular levels of cyclic AMP (cAMP). Elevated cAMP disrupts the ion transport systems in enterocytes, resulting in the secretion of chloride ions (Cl⁻) and water into the intestinal lumen, while inhibiting the absorption of sodium ions (Na⁺). The result is the profuse watery diarrhea characteristic of cholera.
Clinical Features:
- The diarrhea is described as “rice water stools” due to its pale, watery appearance with flecks of mucus.
- Rapid fluid loss can lead to severe dehydration, hypotension, and metabolic acidosis.
- If untreated, the condition may result in shock and death, especially in vulnerable populations like children and the elderly.
Importance of Prompt Treatment:
The key to managing cholera is aggressive rehydration therapy, either orally with rehydration solutions or intravenously in severe cases. Antibiotics, such as doxycycline or azithromycin, may also be used to shorten the duration of symptoms.
Other options (b, c, and d) are associated with different toxins or pathogens but do not cause the hallmark symptoms of cholera toxin.