**Core Concept**
Filariasis is a parasitic disease caused by **Wuchereria bancrofti** and **Brugia malayi**, transmitted through mosquito vectors. The disease affects the lymphatic system, leading to **lymphedema** and **elephantiasis**. The immune response to filarial infection involves both **cell-mediated immunity** and **humoral immunity**.

**Why the Correct Answer is Right**
The correct answer is related to the fact that **humoral immunity** does not play a dominant role in filariasis. Instead, **cell-mediated immunity** is more crucial in controlling the infection. The disease is usually **bilateral**, and humans are the primary host, but other animals can also be infected.

**Why Each Wrong Option is Incorrect**
**Option A:** This statement is true, as morbidity does increase with age in endemic areas due to repeated exposure to infected mosquitoes.
**Option C:** This statement is false, as filariasis is usually **bilateral**, affecting both sides of the body.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that filariasis is a major cause of **lymphedema** and **elephantiasis**, and its control relies on **mass drug administration** and **vector control**.

**Correct Answer:** B. Humoral immunity plays dominant role