**Core Concept**
Trypanosomiasis, specifically Chagas disease, is a parasitic infection caused by the protozoan *Trypanosoma cruzi*. It's transmitted primarily through the bite of an infected triatomine bug, and can lead to serious cardiac and gastrointestinal complications if left untreated.

**Why the Correct Answer is Right**
The drug of choice for Chagas disease is nifurtimox, an antiparasitic medication that targets the parasite's redox enzymes, such as trypanothione reductase. This enzyme is crucial for the parasite's survival and replication. Nifurtimox works by generating free radicals that damage the parasite's DNA, ultimately leading to its death. It's typically used in the acute phase of the disease, and in some cases, may be used in the chronic phase as well.

**Why Each Wrong Option is Incorrect**
**Option A:** Benznidazole is an alternative antiparasitic medication used to treat Chagas disease, but it's not the first-line treatment. It has a similar mechanism of action to nifurtimox, targeting the parasite's trypanothione reductase enzyme.
**Option B:** Doxycycline is an antibiotic, not an antiparasitic medication, and is not effective against *T. cruzi*. It's used to treat bacterial infections, not parasitic ones.
**Option C:** Metronidazole is an antibiotic and antiprotozoal medication, but it's not the preferred treatment for Chagas disease. It's more commonly used to treat infections caused by *Giardia* and *Trichomonas*.

**Clinical Pearl / High-Yield Fact**
Nifurtimox is the only FDA-approved medication for the treatment of Chagas disease, and its use is limited to the acute phase of the disease. It's essential to diagnose and treat Chagas disease early to prevent long-term cardiac and gastrointestinal complications.

**Correct Answer: B. Benznidazole**