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 'encysted' (hypobiotic) thrid stage larvae from the intestinal wall, and horses are usually affected during late winter or early spring.

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. This type of cyathostomosis is more commonly seen in younger horses who have not developed full immunity.

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. Geriatric animals also have an increased susceptibility.

Clinical Signs

Acute disease:

• Acute onset, profuse diarrhoea
• Sudden weight loss
• Pyrexia

Chronic disease:

• Poor quality coat
• Diarrhoea
• Loss of condition
• Stunted growth
• Increased or decreased appetite
• Recurrent colic

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. Adult and larval worms may cause damage to the intestinal mucosa through plug feeding, resulting in ulcer formation.

Diagnosis

Large numbers of thread-like larvae in faeces The clinical features of cyathostomosis are relatively non-specific so diagnosis may not be straightforward. Faecal egg counts may not be useful as the disease manifests due to the presence of larvae.

Laboratory tests

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

• Hyperglobulinaemia (especially IgG)
• (Microcytic) anaemia
• Neutrophilia
• Hypoalbuminaemia

Gross examination of faeces may reveal bright red fourth or fifth stage larvae, and 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.

Intestinal biopsy via laparotomy may may reveal a massive eosinophilic infiltration of the mucosa.

Pathology

Post mortem examination of the large intestine may reveal larvae in the mucosa, seen as small grey to red mucosal nodules (the characteristic 'pepper-pot' lesions seen with the disease). Mass emergence results in mucosal erosions, ulcers and fibrinous exudate. 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. Adult worms (approximately 1.5cm in length) may be seen within the intestinal lumen.

Treatment

Treatment is indicated for faecal egg counts > 200 eggs/gram. Cyathostomins are widely resistant to anthelmintics, particularly benzimidazoles. Moxidectin PO is effective against these resistant strains and also against encysted larvae. Refractory cases may benefit from concurrent corticosteroid therapy with prednisolone. Twice-weekly removal of manure from pastures is recommended.

Prognosis

Guarded

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

• Edward Robinson, N and Sprayberry, K. A. (2009) Current Therapy In Equine Medicine Sixth edition Saunders Elsevier

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

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.