VPA 211: General Veterinary Parasitology and Helminthology (3+1)

LIFE CYCLE

• Eggs of the worms are usually coughed up and swallowed by the birds and voided in the droppings.
• Under optimal condition, the infective stage (L3) is reached in about 3 days. L3 occur inside the egg.
• The infective stage hatch out from the egg, soon it becomes inactive. Infective stage may be ingested by transport host like earthworm, snail and slug.
• Inside the transport host the larvae are encysted and remain viable for several months. Sometimes the egg may not hatch in the environment or outside the host.
• Infection of final host occurs in 3 ways,
• Ingestion of embryonated eggs having L3 stage.
• Ingestion of L3 larva along with feed.
• Ingestion of infected transport host.
• After ingestion, L3 stage penetrate the intestinal mucosa and reaches blood stream and then carried by blood to lungs in about 6 hrs.
• In the lungs, L3 stage is found in alveoli, where further two moults (L4 and L5) occurs in 3 days of infection.
• Young worms migrate to larger bronchi, where copulation takes place and reach the trachea in about 7th day of infection.
• Prepatent period is 17 to 20 days.