**Core Concept**
Paragonimiasis is a parasitic lung infestation caused by the lung fluke *Paragonimus westermanii*, which is acquired through the ingestion of contaminated crustaceans. This condition is characterized by symptoms such as cough, chest pain, and hemoptysis due to the fluke's encystment in lung tissue.

**Why the Correct Answer is Right**
*Paragonimus westermanii* is a large, flattened trematode (fluke) that inhabits the lungs of mammals, including humans. After ingestion of contaminated crustaceans like crabs or crayfish, the eggs hatch in the duodenum, and the larvae penetrate the intestinal wall to reach the bloodstream, eventually lodging in the lungs. There, they encyst and cause the characteristic symptoms of paragonimiasis. The cysts can be detected on chest radiographs, and the diagnosis is confirmed by serological tests or histopathological examination.

**Why Each Wrong Option is Incorrect**
**Option A:** *Hymenolepis nana* (H. nana) is a dwarf tapeworm that primarily infests the small intestine and is not associated with lung infestation.

**Option C:** *Taenia saginata* is a beef tapeworm that primarily infests the small intestine and is not associated with lung infestation.

**Option D:** *Echinococcus granulosus* is a tapeworm that causes hydatid disease, primarily affecting the liver, lungs, and other organs through cyst formation, but it is not the primary cause of lung infestation.

**Clinical Pearl / High-Yield Fact**
Paragonimiasis is often misdiagnosed as pulmonary tuberculosis due to similar symptoms, but the presence of cysts in the lungs and a history of eating contaminated crustaceans can lead to the correct diagnosis. It is essential to consider this diagnosis in patients with unexplained lung symptoms and a history of eating raw or undercooked seafood.

**✓ Correct Answer: B. Paragonimus westermanii**