Bursate Nematodes (Order Strongylida: Haemonchus, Ostertagia, Trichostrongylus, Ancylostoma, Syngamus, Metastrongylus)

• Role of Earthworms as Paratenic Hosts:
• paratenic (transport) host is an intermediate carrier in which a parasite larva survives and remains infective without undergoing necessary morphological development.
• Syngamus trachea (Gapeworm of poultry):
• Earthworms (Eisenia foetida, Lumbricus terrestris) ingest infective $L_3$ larvae of S. trachea from contaminated soil.
• The larvae encyst in the earthworm's body musculature and can persist for years. When birds consume the earthworm, larvae excyst, penetrate the intestinal wall, and migrate to the trachea.
• (For Metastrongylus apri, the earthworm is an obligatory biological intermediate host, not merely a transport host).
• nalysis:
• (Syngamus trachea): Correct.

Correct option: (3) Syngamus trachea