Grass Sickness

Grass Sickness



Basic Information image



Definition


Neurologic disease primarily associated with the degeneration of neurons in the autonomic nervous system, particularly the enteric nervous system



Synonym(s)


Equine dysautonomia



Epidemiology



Species, Age, Sex


Grass sickness most commonly affects horses between 2 and 7 years of age. Older horses rarely develop the disease, possibly because of the development of immunity or tolerance to the causative agent. The disease is very rare in foals and weanlings.



Genetics and Breed Predisposition


All Equids appear to be susceptible to grass sickness, with the disease having been reported in horses, ponies, donkeys, and captive exotic Equidae. There is no breed predisposition.



Risk Factors


Numerous risk factors have been identified, including:



• Cool weather temperatures (7°–11° C) and dry weather with irregular ground frosts in the preceding 2 weeks


• Horses in good or fat body condition


• Higher numbers of horses and the presence of young horses on the premises


• Sandy soils and loam soils


• Increased levels of soil nitrogen


• Previous occurrence of grass sickness on the premises


• Grazing grass: The disease is extremely rare in horses with no access to grass. Co-grazing with ruminants gives some protection from the disease.


• Dietary change


• Movement or recent stress, especially movement to a new pasture in the preceding 2 to 4 weeks


• Pasture disturbance (eg, construction or mole activity)


• High-frequency use of anthelmintics and specific use of ivermectin for ultimate and penultimate treatments


• Mechanical removal of feces from the pasture


• Pasture cutting



Geography and Seasonality




• The northeast region of Scotland has the highest incidence of grass sickness, but the disease is also recognized throughout the United Kingdom as well as in many other Northern European countries, including Norway, Sweden, Denmark, France, Switzerland, and Germany. The disease does not occur in Australasia, Asia, Africa, North America, or Ireland. A clinically and pathologically identical disease known as mel seco (dry sickness) occurs in South America.


• Cases of equine grass sickness may occur throughout the year, but there is a significant peak in incidence in the northern hemisphere in the spring and early summer.



Clinical Presentation



Disease Forms/Subtypes


Grass sickness can be divided into three subdivisions—acute, subacute, and chronic—which are characterized clinically by varying degrees of gastrointestinal immotility and dysphagia, although it should be emphasized that there is a continuum. The acute and subacute forms of the disease are invariably fatal; however, a proportion of mildly affected horses with the chronic form may survive.



History, Chief Complaint




• Acute form


image The onset and progression of clinical signs is rapid, with death occurring in less than 48 hours.

image Animals usually present with depression or somnolence, inappetence, and rapid progression to varying degrees of abdominal pain in many cases.

image The degree of colic may, however, be relatively mild and inconsistent with the profound elevation in pulse rate.

• Subacute form


image Clinical signs are generally similar to but less severe than those of acute cases. Their duration is longer, and the outline of the abdomen quickly develops a marked “tucked-up” appearance.

image This finding does not appear to be entirely attributable to loss of body condition, although significant weight loss does become apparent.

• Chronic form


image Clinical signs in the chronic form are more insidious in onset.

image The most obvious signs include severe weight loss with the development of a distinct “tucked-up” abdomen. Affected horses often have a very base narrow stance, thus adopting the characteristic “elephant on a tub” posture.

image Some horses show apparent weakness, and a reduced anterior phase to the stride results in occasional toe dragging.


Physical Exam Findings




• Acute form


image Dehydration is usually present, which can be demonstrated by prolonged tenting of the skin. A generalized, marked reduction in intestinal motility is evident during abdominal auscultation.

image Bilateral ptosis may or may not be present.

image Muscle fasciculations of the triceps and quadriceps muscle groups may be observed, and sweating may be generalized or localized to the flanks, neck, and shoulder regions.

image Dysphagia is almost invariably present but may be difficult to appreciate because of coexisting inappetence. It may be apparent, however, when observing the animal attempting to drink, when many affected horses flick their muzzles through the water or “paw” at the water bucket, presumably because of frustration.

image Excessive dribbling of saliva is often present and probably results from a combination of excessive saliva production and a reduced ability to swallow.

image Some horses show spontaneous gastric reflux with foul-smelling green or brown fluid exiting from both nostrils. As the disease progresses, abdominal distension becomes apparent in most cases.

• Subacute form


image Affected animals are almost invariably dysphagic.
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Jul 24, 2016 | Posted by in SMALL ANIMAL | Comments Off on Grass Sickness

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