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

LIFE CYCLE

• Man acquires infection by ingestion of infected meat containing viable cyst. Following ingestion, the cyst reach the stomach.
• In the stomach, larvae escape from the cyst in about 5 hrs of infection. Liberated larvae penetrate the stomach mucosa, where it moult to become L1 - L2 and L2 - L3.
• L3 reaches intestine and moult to become L4. Sexual differentiation and copulation occurs in the intestine.
• After copulation, the male will die, while the female enter into the intestinal mucosa, where it produces large number of larvae.
• The newborn larvae enter into the lymphatic vessel and then migrate to left superior vena cava via thoracic duct and finally enters into systemic circulation.
• Through blood, it is distributed to different parts of body.
• Further development occurs in various organs like tongue, diaphragm etc. It is also found in kidney and liver.
• The larvae enter the striated muscle, become encapsulated by muscle fibre.
• These parasitised muscle cell undergoes modulation or redifferentiation in the structure is called as "Nurse cell".
• Function of nurse cell is larval nutrition and handling of waste product. The larvae occurs in lemon shaped cyst in a coiled position. 

Trichinella Larva in Musle cyst