**Core Concept:** Echinococcosis is a zoonotic disease caused by tapeworms of the genus Echinococcus. Echinococcosis granulosus is caused by Echinococcus granulosus, which primarily infects animals like sheep, goats, and cattle, but can spill over to humans as a zoonotic infection.

**Why the Correct Answer is Right:** The definitive host for Echinococcus granulosus is a carnivorous animal, which completes the life cycle of the parasite. In this case, the correct answer is **C. Canis familiaris (domestic dog)**. Dogs act as the definitive host because they ingest the metacestode (adult tapeworm) eggs through contaminated food or water, which then mature into adult tapeworms in the dog's small intestine. These adult tapeworms shed eggs into the feces, which can contaminate the environment and lead to infection of the intermediate hosts (sheep, goats, cattle) when ingested by grazing animals.

**Why Each Wrong Option is Incorrect:**

A. **Mammals (Bovines):** While bovines can act as intermediate hosts, they are not correct as definitive hosts because the parasite's life cycle is completed in dogs.

B. **Canis familiaris (domestic cat):** Domestic cats can also act as definitive hosts for echinococcosis, but the question specifies "dogs" as the definitive host.

C. **Canis familiaris (domestic dog):** As explained above, dogs are the correct definitive host for Echinococcus granulosus.

D. **Human (Homo sapiens):** Humans can act as intermediate hosts, but they are not the definitive host because the life cycle is completed in dogs or cats.

**Clinical Pearl:** Understanding the life cycle of Echinococcus granulosus is crucial for recognizing human infection, which can lead to abdominal pain, hepatomegaly, and splenomegaly due to cyst formation in the liver and/or lungs. Early diagnosis and treatment are essential to prevent complications like rupture and spillage of tapeworm eggs into the peritoneal cavity or pleural cavity, leading to potential life-threatening situations.