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

Bionomics of strongyle larva

BIONOMICS OF STRONGYLE LARVAE

The L1 hatch out from the eggs, L1 have rhabditiform oesophagus.

• L1 mainly feeds on bacteria and grows rapidly, then enter into the lethargic state and moult to L2.
• L2 also feeds on bacteria, soon after lethargic state the L2 moult to L3. L2 have less rhabditifrom oesophagus.
• L3 have filariform oesophagus, it is a infective stage. Cuticle of L2 is retained as a protective sheath around L3. Which is very important for survival of infective stage. Since L3 wrapped with cuticle of L2 it does not feed. L3 thrive on the stored food materials in the intestinal cells. Infective stage is negatively geotropic and positively phototropic to mild sunlight, but it will be repelled by strong sun light. L3 larva crawls on grass blades in early morning, evening and during dull weather. L3 survive upto 3 months.
• Infection of horse by ingestion of L3 along with herbage or vegetations.
• Exsheathment occurs in the small intestine of horse.
• After exsheathment, L3 penetrate the intestine wall where L3 moult to become L4 in about 3 days of infection. These L4 penetrate the intima of submucosal arterioles and migrate towards the cranial mesenteric artery. In the cranial mesenteric artery it produces thrombus and later aneurysm in about 14 days of infection. From 45 days of infection onwards the L4 pass back to submucosa of caecum and colon via arterial system. In the submucosa of caecum and colon L4 moult to L5. Then L5 enter into the lumen of intestine and reach maturity in about 3 months.