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MCQs in Tropical Medicine

Rob Skelly DTM+H FRCP

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Answer 36


False a. Vibrio cholera of the 01 serotype is the only cause of clinical disease
True b. low gastric pH protects against infection
False c. cholera toxin produces its effect by reducing intracellular levels of cAMP
True d. hypoglycaemia is a recognised complication in children
False e. fever is usual in adults

a. Until recently the only V.cholera serotype known to cause cholera was the 01 serotype. Quite recently V.cholera 0139 (Bengal) was isolated as the cause of epidemic cholera. It has a different lipopolysaccharide coat and there is little or no herd immunity.

b. 100,000,000-10,000,000,000 organisms are required to produce infection as most are destroyed by gastric acid. Hypochlorhydria may allow cholera to develop following a smaller inoculating dose.

c. cholera toxin is an 84kDa protein consisting of one A (activating) and five B (binding) subunits. The A1 part of the A subunit enters the mucosal cell. Here it catalyses the transfer of ADP-ribose to GTP-binding regulatory protein. GTP regulatory protein is altered in conformation and this leads to reduced inhibition of adenyl cyclase. The intracellular concentration of cAMP rises and a net loss of isotonic fluid into the gut occurs.

d. Complications of cholera in children include hypoglycaemia, shock, hypothermia, hypokalaemia, coma, vomiting and aspiration pneumonia.

e. Fever may occur in children

Copyright: Rob Skelly 2006