Question

Tracheal route of migration is found in
(A) Toxocara canis
(B) Toxascaris leonina
(C) Ascaris suum
(D) Parascaris equorum
Choose the correct answer from the options given below:

• A. (A), (B) and (D) only.
• B. (A), (C) and (D) only.
• C. (A), (B), (C) and (D).
• D. (B), (C) and (D) only.

Hint:

Remember that Toxascaris leonina is the unique exception among common domestic animal ascarids as it has no migratory phase outside the digestive tract. Eliminating (B) from the options immediately points to the correct answer.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Tracheal migration (also called hepato-tracheal migration) is a common larval migratory pathway in some ascarid nematodes where infective larvae hatch in the gut, migrate to the liver, then to the lungs, crawl up the trachea, are swallowed, and mature in the small intestine.
Detailed Explanation:
Let us analyze the migration pathways of the given ascarid species:
- (A) Toxocara canis: In young puppies ($<$ 3 months), larvae undergo classic hepato-tracheal migration (tracheal route). In older dogs, somatic migration is more common. Thus, (A) features tracheal migration.
- (B) Toxascaris leonina: This parasite does not exhibit any extra-intestinal migration. Larvae hatch and develop entirely within the mucosal wall of the gut (direct development). Thus, (B) does not have tracheal migration.
- (C) Ascaris suum: Larvae in pigs undergo mandatory hepato-tracheal migration before settling in the small intestine. Thus, (C) features tracheal migration.
- (D) Parascaris equorum: The foal roundworm relies on the hepato-tracheal route to complete its lifecycle. Thus, (D) features tracheal migration.
Therefore, tracheal route of migration is found in (A), (C), and (D).

Step 2: Final Answer:
The correct combination is (A), (C) and (D) only, which corresponds to Option (B).