Grass sickness

Grass sickness, alternatively termed equine dysautonomia, is a rare but predominantly fatal illness in horses. Grass sickness may affect all types of horse, pony and donkey, and has affected some well known horses including the thoroughbred stallions Dubai Millennium, Moorestyle and Mister Baileys.

Clinical signs

Grass sickness is a polyneuropathy affecting the central, peripheral and enteric nervous systems.^[1] The majority of visible clinical signs are related to paralysis within the digestive tract although nerve damage occurs throughout the body. There are three forms of grass sickness:

• acute grass sickness (AGS) - horses display signs of colic and require euthanasia or die within 48 hours
• subacute grass sickness (SAGS) - horses display clinical signs similar to AGS but with less severity and may survive up to 7 days
• chronic grass sickness (CGS) - horses present with severe and rapid weight loss and a selected portion of these cases may survive.

Clinical signs common to all subsets include: depression, anorexia, colic (moderate with AGS/SAGS and mild with CGS), excess salivation, constipation, nasogastric fluid secretion, patchy sweating, muscle tremors and eyelid drooping.

Cause

The cause remains unknown, but the toxin produced from the bacterium Clostridium botulinum type C may be involved.^[2]

Clostridium botulinum is a soil-borne bacterium, which may be better known for producing clinical signs of botulism. It may cause grass sickness when the spores of C. botulinum type C are ingested and produce their toxin locally within the intestine.

It is also linked to pasture mycotoxicosis, which comprises a very large and diverse population of

The first cases of grass sickness were recorded in eastern Scotland in 1909.^[4]

References