Intermediate host for hydatid disease –
**Core Concept**
Hydatid disease, also known as echinococcosis, is a parasitic infection caused by the larval stage of the Echinococcus tapeworm. The lifecycle of Echinococcus involves two hosts: an intermediate host where the larva develops, and a definitive host where the adult tapeworm resides. The intermediate host for hydatid disease is typically a mammal, usually sheep, goats, or cattle, where the larva forms a cystic structure.
**Why the Correct Answer is Right**
The intermediate host for hydatid disease plays a crucial role in the lifecycle of Echinococcus. When an intermediate host ingests the eggs of Echinococcus, the larvae hatch and penetrate the intestinal wall, eventually reaching the liver and other organs via the bloodstream. The larvae then form cystic structures, known as hydatid cysts, which can grow and cause tissue damage. The definitive host, usually a canine, ingests the viscera of an infected intermediate host, allowing the adult tapeworm to establish itself in the small intestine.
**Why Each Wrong Option is Incorrect**
* **Option A:** Incorrect because it is not a recognized intermediate host for hydatid disease.
* **Option B:** Incorrect because it is a definitive host, not an intermediate host, for Echinococcus.
* **Option C:** Incorrect because it is a human disease that can result from ingesting contaminated food or water, but humans are not typically considered intermediate hosts.
**Clinical Pearl / High-Yield Fact**
Humans can become accidental intermediate hosts for Echinococcus, typically through ingesting contaminated food or water. This highlights the importance of proper food handling and hygiene practices to prevent the spread of hydatid disease.
**Correct Answer:** D.