**Core Concept**
Japanese encephalitis is a zoonotic disease caused by the JE virus, primarily transmitted through the bite of an infected mosquito vector. The concept of an amplifier host is crucial in understanding the transmission dynamics of this disease.

**Why the Correct Answer is Right**
The correct answer is **C. Pig**, as pigs serve as the primary amplifier host for Japanese encephalitis virus (JEV). When infected pigs are bitten by mosquitoes, they amplify the virus, making them a crucial link in the transmission cycle. This process increases the viral load in the mosquito population, which in turn enhances the risk of transmission to humans. The JEV replicates in the pig's peripheral tissues, particularly in the lymphoid organs, and is excreted in saliva, urine, and feces, making them a potential source of infection for mosquitoes.

**Why Each Wrong Option is Incorrect**
**Option A:** Not relevant to Japanese encephalitis transmission.
**Option B:** Cattle are not the primary amplifier host for JEV.
**Option D:** Humans are not the primary amplifier host for JEV.

**Clinical Pearl / High-Yield Fact**
Pigs are the primary amplifier host for Japanese encephalitis virus, and controlling the pig population can help reduce the transmission of JEV to humans.

**Correct Answer:** C. Pig.