Question

Assertion (A): Elephantiasis is due to the obstruction of lymphatic vessels by accumulation of dead filarial worms.
Reason (R): First stage microfilaria larva is the infective stage to humans.

• A. Both (A) and (R) are true. (R) is correct explanation for (A)
• B. Both (A) and (R) are true. (R) is not correct explanation for (A)
• C. (A) is true. But (R) is false
• D. (A) is false. But (R) is true

Hint:

The vector for Wuchereria bancrofti is the female Culex mosquito.
The infective stage for humans is always the third-stage (L3) filariform larva.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question presents an Assertion regarding the cause of lymphatic obstruction in elephantiasis, and a Reason concerning the infective larval stage of the filarial parasite.

Step 2: Key Concepts and Approach:
We analyze the life cycle and pathogenesis of the nematode Wuchereria bancrofti (the filarial worm), which causes lymphatic filariasis.

Step 3: Detailed Explanation:

• Assertion (A): Adult filarial worms (Wuchereria bancrofti) live in the lymphatic vessels and lymph nodes of humans.
When the adult worms die, they trigger a strong inflammatory response.
This leads to connective tissue growth and chronic obstruction of the lymphatic vessels.
The blocked lymph fluid causes severe swelling in the lower limbs and scrotum, a condition known as elephantiasis. Thus, Assertion (A) is true.

• Reason (R): The first-stage larva (microfilaria) is released into the human bloodstream and is ingested by female Culex mosquitoes.
Inside the mosquito, the larva molts into the third-stage (L3) filariform larva.
This L3 larva is the actual infective stage transmitted back to humans during a mosquito bite.
Thus, the first-stage microfilaria is not the infective stage to humans, making Reason (R) false.


Step 4: Final Answer:
Assertion (A) is correct, but Reason (R) is incorrect, corresponding to option (C).