## **Core Concept**
Amoebiasis, caused by *Entamoeba histolytica*, is primarily transmitted through the fecal-oral route. The parasite exists in two forms: the infectious cyst form and the non-infectious trophozoite form. Transmission typically occurs through contaminated food, water, or hands.

## **Why the Correct Answer is Right**
The correct answer, ., involves understanding the lifecycle and transmission modes of *E. histolytica*. The parasite's cysts are resilient and can survive outside the host, making them the primary form of transmission. This usually occurs through:

- Contaminated water
- Food handled by infected individuals
- Direct fecal-oral contact

## **Why Each Wrong Option is Incorrect**
- **Option A:** . This option is incorrect because *E. histolytica* cysts can indeed be transmitted through contaminated food.
- **Option B:** . This option is incorrect as well because water contaminated with *E. histolytica* cysts is a well-known mode of transmission.
- **Option C:** . This is also incorrect since direct contact with an infected person's feces can transmit the disease.

## **Why the Correct Answer is Right (Detailed for D)**
- **Option D:** . This is the correct answer because *E. histolytica* is not transmitted through a vector like a mosquito. Vectors typically refer to organisms that transmit pathogens to humans, often through a bite. Amoebiasis transmission does not involve vectors in the traditional sense of arthropods like mosquitoes or ticks.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the diagnosis of amoebiasis often involves demonstrating *E. histolytica* cysts or trophozoites in stool samples. A high-yield fact is that the presence of four nuclei in a cyst is diagnostic for *E. histolytica*.

## **Correct Answer: D. Vector.**