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 with this type of disease are usually affected during late winter or early spring.

The chronic form occurs when ingested third stage 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 of associated with a 'wormy' horse. This type of cyathostomosis is more commonly seen in younger horses who have not yet developed full immunity against the parasite.

Signalment

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

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 ventral oedema due to a protein-losing enteropathy. Adult and larval worms may cause damage to the intestinal mucosa through plug feeding, resulting in ulcer formation.

Diagnosis

The clinical features of cyathostomosis are relatively non-specific and confirming a diagnosis of cyathostomosis may be difficult. Faecal egg counts may not be useful as large numbers of eggs in the faeces do not always indcate a pathological worm burden. Affected horses may show the following abnormalities on haematology and biochemistry:

Hyperglobulinaemia (especially IgG)
(Microcytic) anaemia
Neutrophilia
Hypoalbuminaemia

Gross examination of faeces may reveal large numbers of small, thread like larvae. Larvae may also be found on the plastic sleeve following rectal examination.

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' lesion). 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 horses with faecal egg counts greater than 200 eggs per 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.

Prognosis

Approximately 40% of horses affected with acute diarrhoea from larval cyathosomosis will recover if treated appropriately.

Prevention

Good grazing management such as regular manure removal, harrowing, pasture rotation and grazing horses with ruminants all aid in reducing pasture contamination. Anthemlintic programs should only be used as an adjunct to good hygiene and management practices.

References

Fox, M and Jacobs, D. (2007) Parasitology Study Guide Part 2: Helminths Royal Veterinary College

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