Cyathostomosis

Also known as:

Cyathostominosis

Description

Cyathostomins are also known as small strongyles, and are one of the most important gastro-intestinal parasites of the horse. Over 40 species and several genera have been identified. The small, thread-like worms inhabit the caecum and the large colon with their developmental stages confined to the mucosa of the large intestine. Unlike the large strongyles, they do not undergo any extra-intestinal migration during development.

Both an acute and chronic form of larval cyathostomosis occur in horses. The acute form occurs due to the re-emergence of hypobiotic thrid stage larvae from the intestinal wall, and horses are usually affected during late winter or early spring. It is usually individual, susceptible animals that are affected.

The chronic form occurs when ingested larvae develop to the fourth stage without interruption, leading to inflammation and thickening of the intestinal mucosa. Larval emergence may occur throughout the summer and autumn, leading to the clinical signs associated with a 'wormy' horse.

Signalment

All horses may be affected but most are less than five years old. Disease commonly occurs in late winter or early spring. A history of an unthrifty or 'poor do-ing' young horse combined with identifcation of larvae in faeces may arouse clinical suspicion of cyathostomosis.

Diagnosis

The clinical features of cyathostomosis are relatively non-specific so diagnosis may not be straightforward.

Clinical Signs

Acute disease:

• Acute onset, profuse diarrhoea
• Pyrexia

• Large numbers of thread-like larvae in faeces
• Marked, rapid weight loss
• Poor quality coat
• Increased or decreased appetite
• Pyrexia
• Lethargy

Other clinical features of the disease include oedema due to a protein-losing enteropathy. Emergence of larvae from the intestinal wall may lead to haemorrhagic colitis

Laboratory tests

Affected horses may show the following abnormalities on haematology and biochemistry:

• Hyperglobulinaemia (especially IgG)
• Anaemia
• Neutrophilia
• Hypoalbuminaemia

Gross examination of faeces may reveal bright red fourth or fifth stage larvae. Larvae may be found on the rectal sleeve following examination. Faecal egg counts may be low due to the disease being caused by emerging larvae.

Pathology

Post mortem examination of the large intestine may reveal larvae in the mucosa, seen as small grey dots (the characteristic 'pepper-pot' lesions seen with the disease). A catarrhal and haemorrhagic colitis and typhlitis may be seen, with hyperaemia or necrosis of the tissue. In chronic cases, thickening of the intestinal wall may be present.

Treatment

Treatment of cyathostomosis is based on intensive anthelmintic medication (fenbendazole and ivermectin) combined with concurrent corticosteroid therapy with prednisolone.

References

• White, N.A., Edwards, G.B. 1999 Handbook of Equine Colic) Reed Educational and Professional Publishing Ltd

• Mair, T., Love, S., Schumacher, J. and Watson, E. (1998) Equine Medicine, Surgery and Reproduction WB Saunders Company Ltd

• Knottenbelt, D.C. A Handbook of Equine Medicine for Final Year Students University of Liverpool

• Pearce, O. (1994) Treatment of Equine Tetanus In Practice November 1994 pp 322-325.

• Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition) Merial

Gross

• Encysted larvae appear as pinhead grey to red mucosal nodules.
• Mass emergence results in:
  • Mucosal erosions.
• Ulcers.
• Fibrinous exudates.
• Haemorrhage.

Histopathology

• Larvae in deep mucosa/sumucosa surrounded by fibrous capsule and mixed inflammatory cells.
• Intense eosinophil, neutrophil and macrophage infiltration when larvae emerge
  • May also be oedema and, if severe, mucosal ulceration.