Grass Sickness
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This article is still under construction. |
Description
Equine grass sickness, or equine dysautonomia causes a paralysis of the gastro-intestinal tract, by disruption of the autonomic nervous system. This leads to a pooling of ingesta throughout all parts of the gastro-intestinal tract. The condition may occur acutely, or progress chronically over several weeks, but all cases will eventually die. A definitive diagnosis is obtained by taking an ileal biopsy, and inspecting the intrinsic myenteric plexus. There is no effective treatment, although in the short to medium term, horses can be successfully managed by informed and attentive owners.
Signalment
Cases of Grass sickness are restricted to Northwestern Europe and South America with the highest incidence in the UK, in some parts of Eastern Scotland 1% of horses die annualy from the disease. Young animals, 2-7 years old are predisposed. The disease occurs in warm wet weather with peak incidences in spring and autumn. Affected horses usually live at pasture, those that have moved pasture within the preceeding two months are also at greater risk. In many cases the disease appears to be related to specific pstures or fields with a history of grass sickness affected horses, however it has been reported in animals with none of the usual risk factors.
Diagnosis
Clinical signs
- Depression
- Abdominal pain, episodes of colic
- Abdominal distension
- Dysphagia
- Inappetence
- Muscular tremors
- Reduced faecal output
- Hypersalivation
- Degenerative lesions are seen in the autonomic nerve ganglia, including enteric plexuses
- This is very unlikely, and the condition is usually fatal.
- Clinically difficult to diagnose - signs are confined to the gut.
- Easy to diagnose on post mortem
Pathology
- Stomach and small intestine large amounts of contain watery yellow fluid.
- There is an abrupt change in the large intestine, where no fluid is present.
- large intestine has very dry mucoid contents.
- There is an abrupt change in the large intestine, where no fluid is present.
- Stomach and small intestine large amounts of contain watery yellow fluid.
Pathogenesis
- Due to functional obstruction at ileocaecal valve and a degree of paralytic ileus of the small intestine.
- The exact cause is unknown, but a type of bacterial or fungal toxin which may damage autonomic nervous system ganglia may be involved.
- Clostridium botulinum is thought to be involved.
- A similar condition seen in hares
- A definitive diagnosis must be made - if the condition is due to the grazing we need to know.
- E.g. if on livery or stud grazing, may put people off going there.
- A definitive diagnosis must be made - if the condition is due to the grazing we need to know.
- 'Diagnosis
- At post mortem look for degenerative changes in coeliaco-mesenteric ganglia - need to examine histologically.
- Ganglia are peanut sized and found in perirenal fat between adrenal gland and the aorta.
- At post mortem look for degenerative changes in coeliaco-mesenteric ganglia - need to examine histologically.
Treatment
Prompt euthanasia is indicated in acute and per acute cases, some chronic cases can be managed with intensive nursing care for a limited time period.
Prognosis
The condition is fatal.
References
- Knottenbelt, D.C. A Handbook of Equine Medicine for Final Year Students University of Liverpool
- Rose, R. J. and Hodgson, D. R. (2000) Manual of Equine Practice (Second Edition) Sauders.
| Also known as: | Equine Dysautonomia |