Question

Case Study - Cholera A 25 year old woman is brought into a clinic in Bangladesh during the monsoon season. She is almost comatose, her pulse is weak and she is experiencing tachycardia. She has severe diarrhea, and is producing watery stool at a rate of 950 ml/hr. Her skin appears shriveled, and when a fold of skin is pinched it remains so for several minutes. Microscopic examination of the patient’s stool reveals the presence of a large number of Vibrio cholerae bacteria. The patient cannot drink, so intravenous isotonic NaCl is administered. When the patient is conscious, she is given an oral rehydration solution to drink. It contains NaCl, KCl, NaHCO3 and glucose. After 5 days she is sufficiently recovered to leave the hospital.

1. How did she most likely encounter the bacteria?

2. Why does she exhibit weak pulse and tachycardia? Why is she almost comatose?

3. How did the cholera toxin enter the cells and how did it affect intracellular signal transduction pathways and membrane transport.

4. How do intravenous fluids immediately improve the patient’s condition? Why isotonic NaCl?

5. What is the rationale for the ingredients in the oral rehydration solution?

6. Why does the patient recover in 5 days with this treatment and without antibiotics?

Answer 1

1. Vibrio cholerae bacteria mainly gets transmitted through feco -oral route. Drinking contaminated water or eating contaminated food is the main cause. As it is mentioned in the question that it was rainy season, so chances of contamination is higher in rainy season.

2. The patient had tachycardia and weak pulse because she was suffering from severe dehydration. Because of the infection, large amout of water is being lost in the patient. Due to this, there is more strain on heart which causes tachycardia and weak pulse. Due to dehydration ( because of excessive stool) , water level in body is severely low which makes patient comatose.

3. The cholera toxin is a type of enterotoxin which acts on the cells present in intestine. This toxin activates and promote activity of cAMP. This cAMP transport large amount of sodium from intestinal cells into the lumen. As sodium ion moves, water also move along with them into the lumen. This cause massive loss of water. Thus cholera toxin alters the membrane transport of sodium by shutting off the signal transduction pathway

4. The intavenous fluid ( isotonic NaCl) has the same osmolarity as that of the plasma of blood. Therefore, when iv fluid is given , it replaces the lost volume of fluid due to diarrhoea and improves patient's condition.

5. The composition of oral rehydration solution has the same composition of our body plasma. Thus it replenishes the lost volume of fluid without changing osmolarity of blood. Hence it is used in rehydration.

6. Cholera toxin gets destroyed by itself in 4-5 days because the bacteria has life cycle of 4-5 days inside our body. So just providing symptomatic treatment in the form of rehydration therapy is itself enough for the treatment of cholera.