Dictyocaulosis - Horse

Introduction

Dictyocaulus arnfieldi is the lungworm of horses. The main source of infection are donkeys as these remain infected for years and contaminate horses' pasture. Infection can cycle in horses.

The prevalence of lungworm in horses is around 10-20% whereas in donkeys it is 75%. There are very few adult worms or eggs in the faeces in horses, whereas in donkeys there are many of both present. In horses, the period of patency is around 8 months or less, whereas in donkeys it is around 5 years, hence such a problem occurs when donkeys share pasture with horses. Also, clinical signs are rarely seen in donkeys, unlike horses where signs can be much more severe.

Clinical Signs

Clinical signs vary from none to chronic and include a chronic cough at rest or during exercise in a single animal or in a group of horses. This is most prevalent in autumn or early winter.

Diagnosis

Clinical signs and time of year can be indicative of the disease. History is very important and information such as has co-grazing with donkeys is very important.

Faecal examination can be used but this only detects patent infections, which account for only a small proportion of lungworm infections in horses. The sample must be processed immediately using the McMaster method to search for embryonated eggs. OR the sample can be processed at a later date and the Baerman technique can be used to detect larvae with tail spine.

Tracheobronchial washings can be useful and will show large eosinophil count.

Response to anthelmintic treatment by resolution of clinical signs will provide a retrospective diagnosis.

Treatment and Control

Do not keep horses on pastures grazed by donkeys as these are potential carriers. Treat donkeys with appropriate anthelmintic in spring if grazed with horses. If horses are found to have the disease then treatment with an appropriate anthelmintic is required. If the condition is very severe then supportive treatment with brochodilators may be required.

References

Bertone, J. (2006) Equine Geriatric Medicine and Surgery, Elsevier

Blood, D.C. and Studdert, V. P. (1999) Saunders Comprehensive Veterinary Dictionary (2nd Edition) Elsevier Science

Brown, C.M, Bertone, J.J. (2002) The 5-Minute Veterinary Consult- Equine, Lippincott, Williams & Wilkins

Cowart, R.P. and Casteel, S.W. (2001) An Outline of Swine diseases: a handbook Wiley-Blackwell

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

Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) Equine Internal Medicine (Third Edition), Saunders.