Strongylus vulgaris

Strongylus vulgaris is a clinically important parasite causing verminous arteritis and was a very common cause of colic in horses. Its prevalence has been on the decrease since the use of wormers containing ivermectin.

Appearance

• Dark red
• Well developed buccal capsule in male

Life cycle

The S. vulgaris eggs are shed in the faeces. Under optimal conditions of high humidity and temperatures over 10 degrees, the eggs will transform into rhabditiform L1 larvae within a few days.

They then transform into L2, and subsequently L3 without leaving the parasite envelope. L3 are ingested by the host when feeding on pasture. L3 enter the small intestine, where they shed their envelope, and then begin migration across the muscosal surface, where they transfrom into L4.

L4 reach the arterioles of the intestine. Around 2 weeks after the eggs were first ingested they reach the colic and caecal arteries, and then finally the cranial mesenteric artery.

L4 then transforms into the immature adult and returns to the L1 via the blood vessels. Here they form nodules on the wall of the caecum, and occassionally the colon, and are then released into the lumen.

The prepatent period for S. vulgaris is 6-7 months.

Pathogenesis

By larvae:

• Disruption to endothelium of blood vessel
• May cause arterial thromboembolism in the horse.
• May cause intestinal infarcts, see General Pathology

By adults:

• Accidental damage to blood vessels as a result of feeding on intestinal mucosa