**Core Concept**
Cholera transmission is primarily facilitated by the ingestion of contaminated fecal matter, often through contaminated water or food. The causative agent, Vibrio cholerae, multiplies in the small intestine and produces cholera toxin, leading to severe diarrhea and dehydration.

**Why the Correct Answer is Right**
Cholera toxin, a potent enterotoxin, binds to GM1 gangliosides on intestinal epithelial cells, activating adenylate cyclase and increasing cyclic AMP levels. This results in a massive efflux of water and electrolytes into the intestinal lumen, leading to severe diarrhea and dehydration. The correct answer highlights the primary mode of cholera transmission, which is through contaminated food or water.

**Why Each Wrong Option is Incorrect**
**Option A:** Food transmits - This is correct, as cholera is often transmitted through contaminated food or water.
**Option B:** Vaccination gives 90% efficiency - While vaccines are effective in preventing cholera, their efficacy can vary, and 90% efficiency is not a universally accepted figure.
**Option C:** Healthy carrier - Healthy individuals are not typically considered carriers of cholera, as the bacteria do not colonize their intestines.
**Option D:** Chlorination is not effective - Chlorination is an effective method for disinfecting water and killing Vibrio cholerae.

**Clinical Pearl / High-Yield Fact**
Cholera toxin's mechanism of action is similar to that of other enterotoxins, such as heat-labile enterotoxin (LT) produced by E. coli. Understanding the molecular mechanisms of cholera toxin is crucial for developing effective treatments and vaccines.

**Correct Answer: A**. Food transmits.