Strongylosis

Strongylosis is most frequently a common problem in young horses reared on permanent horse pastures, although cases of severe disease may occur in adult animals kept in suburban paddocks and subjected to overcrowding and poor management.

Etiology

Strongylus is a robust dark red worm easily seen on intestinal mucosa. Eggs are passed in faeces and development of L₃ takes place in an environment. 

Host affected

• Strongylus infection is more severe in foals, adults are resistant to reinfection.

Source of infection

• Infective larvae which have developed during grazing season survived on pasture over winter.
• Eggs passed on current grazing season by nursing horse and shared grazing on same area.

Life cycle

• Infection is by ingestion of the L₃, which penetrate the intestinal mucosa and moult to L₄ in the submucosa.
• These then enter small arteries and migrate on the endothelium to their predilection site in the cranial mesenteric artery and its main branches.
• After a period of certain development the larvae moult to L₅ and return to the intestinal wall (the arterial lumina).
• Nodules are formed around the larvae mainly in the wall of the caecum and colon, when due to their size, they can travel no further within the arteries and subsequent rupture of these nodules releases the young adult parasites into the lumen of the intestine.
• The prepatent period is 6-7 months.

Pathogenesis

• The larvae migrate to cranial messentric artery and its main branches cause thrombus formation provoked by larval damage to the endothelium together with marked inflammation and thickening of arterial wall.
• True aneurysm with dilatation of arterial wall was encountered in repeated infection.

Clinical manifestation

• It usually seen upto 2-3 yrs of age.
• Unthriftiness, poor performance, weight loss, anaemia and diarrhoea.
• Poor appetite.
• Intermittent colic.

Diagnosis

• Based on EPG – 1,000.
• Fecal culture – Identification of L₃ larvae.
• Based on clinical signs.
• Aneurysm in cranial mesenteric artery – palpated through rectal examination (Large pulsating bodies – 6 –7 cm).
• Hyper motility of intestine heard on abdominal auscultation.
• Vertebral percussion -pain evinced on lumbar and sacral region during percussion.

Differential diagnosis

• Anemia is differentiated with babesiosis, equine infectious anaemia, ascariasis and nutritional deficiency in grasses.
• Diarrhoeais is differentiated with salmonellosis.

Treatment

• Treatment may targeted against immature and adult stage.
• Fenbendazole at 30 mg/kg  single dose or Fenbendazole at 7.5 mg / kg daily for 5 days effective against mucosal larvae and kill over 90% of hypobiotic larvae.
• Ivermectin at 0.2 mg/kg is effective against mucosal stage of larvae and  repeated at 8-10 weeks interval.
• Mebendazole at 5-10 mg/kg, Oxibendazole at 10mg/kg is effective against  adult worms.
• Tetrahydropyrimidines-Pyrantel at 19 mg/kg, Pyrantel pamoate at 6.6 mg/kg.

Prophylactic Schedule

• High stocking density & favorable environmental condition – deworm once in six weeks.
• High stocking density & unfavorable environmental condition (winter)- deworm once in two weeks).
• Low stocking density –  deworm once in three months.

Treatment for colic

• If animal have verminous aneurysm give 6 % iron dextran & 5% dextrin through I/V for  antithrombin activity.

Prophylaxis and Control

• Routine anthelmintics – all grazing animals over two months of age treated with broad spectrum anthelmintics (change drugs once in 6 months to prevent anthelmintic resistance)
• Pasture and Grazing management – not over grazed or over stocked
  • Alternative grazing: Horse + Sheep; Horse + Cattle (cattle will assist reduction of larvae burden in the pasture because, strongyles do not infect ruminants).
  • Rotational grazing: nourishing mares and their foals, don’t graze the same area for successive year.
  • Special attention for foals- fed only wholesome fodder.
  • Proper disposal of manure.
  • Heaping of manure will generate heat and destroy eggs.
  • Newly purchased animal should be treated with anthelmintics and quarantine for 48-72 hrs before introduced into herd.