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This article was published in 1948
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.
Nervous Disorders Associated with Roundworm Infestation in Horses
E. J. McBARRON, Inspector of Stock, Holbrook.
During four years in this District the writer has been confronted with syndromes in horses simulating epileptiform seizure. The history has been that the subject was observed standing quietly at pasture or in draught, and "threw a fit." The limbs became rigid, the animal trembled, and might commence to run backwards; finally squatting on its haunches before becoming prostrate. Often it does not advance to this stage, but the owner comments that it threw a fit which lasted ten minutes. Of the five cases seen, the majority were in draught horses up to seven years of age. A fatal termination was seen in two of them.
Opportunity was taken to investigate one case fully, viz.:—
Subject: White draught mare, seven years old, used as a carthorse for medium draught.
History: Had been 18 months on the property and never previously ill except for one bout of "colic" three months previously. In the last week had been transferred to a lucerne paddock and fed on oaten hay at midday. No grain had been fed to the horse for two months. Duties involved carting feed to sheep in paddocks, the draught never exceeding half a ton at any time, but on 15/5/45 a heavier load than usual was carried and hauling was over a ploughed paddock: though this did not appear to extend the animal. A capricious appetite was noted at the midday meal on 15/5/45. Before being turned out at 5.30 p.m., the mare commenced to scour: it was so profuse that it gathered in the cart. Scouring was of short duration, then ceased, and the mare trotted away with other horses. On the morning of 16/5/45 the affected horse was seen to be standing about, slobbering at the mouth and breathing heavily. The owner commented that the heart was thumping, having put his hand on the sternum. There was no straining nor scouring, but there appeared to be some difficulty in micturating. About half an hour after the first observation the mare commenced to sway and stagger, the hind limbs collapsed and for a moment it was sitting on its haunches. It then adopted a lateral recumbency, sitting up for a short while, but soon reverted to the former position. Pressure on the thorax in lateral recumbency appeared to cause the subject great pain. Within twenty minutes the animal "flattened out," gave one or two gasps and died (8.45 a.m.).
Examination: 3 p.m. 16/5/45. Tail and hocks were stained with faeces, partly undigested. There were signs of struggling prior to death. Visible mucous membranes highly injected. Rigor mortis had set in but the body was still warm. There was marked tympany but no protrusion of the rectum. Pressure on the abdomen caused the discharge of about two litres of light, straw coloured faecal matter from the rectum.
Post-mortem: 3.10 p.m., 16/5/45. Subcutaneous tissues dry. Peritoneal cavity contained a small quantity of dark-coloured fluid. The peritoneum, both visceral and parietal, adjacent to the stomach and small intestine showed an early developing peritonitis. The peritoneum of the posterior portion of the abdomen and pelvis was normal.
The small intestine contained yellow fluid material, and a large number of roundworms (Ascaris equorum). The infestation was so heavy that portions of the gut were packed with them; over 42 in various stages of development were recovered from two feet of the bowel. They could be felt as cords in the unopened bowel.
The large intestine and caecum did not appear to contain any worms, but had undergone decomposition compatible with the average cadaver dead for that length of time. The stomach was distended and contained about three dozen bot larvae.
The liver was markedly icteric and had small haemorrhagic areas about one inch in diameter. The kidneys were pale. The blood did not clot and was very thick and tarry. The bladder was empty. The pleural fluid was scant and clear. The lungs were congested: the left lung showed hypostasis. The heart had extensive sub-epicardial and sub-endocardial haemorrhages. The diaphragm had haemorrhagic areas over two inches in diameter.
The whole picture was that of acute Ascariasis; the actual cause of death being toxaemia arising from the damage caused by migrating larvae.
A four-year-old police home, chaff fed, was prone to these fits, and had thrown three at about monthly intervals prior to examination. Examination of the faeces revealed numerous ascarid eggs. A drench was administered and numerous adult ascarids were expelled. No further attacks have occurred in a period of 18 months.
The writer has been unable to find any references to actual nervous disorders in horses due to ascarids. Monnig (1938) states that in dogs nervous symptoms of various kinds may be seen, even such as may lead to a suspicion of rabies. He mentions frequent digestive disturbances and symptoms of colic In horses, especially young foals, Mandoul (1939) describes a substance in Ascaris megalocephala (A. equorum) toxic for the guinea pig. Foster (1942) considers that Ascarids are rarely found in horses over four to five years and outlines the various conditions to which they can give rise.
It is suggested, therefore, that in cases simulating epileptiform seizures in horses, the possibility of a heavy infestation of ascarids be not overlooked.
References:
Monnig, H. O., Veterinary Helminthology and Entomology. 2nd Edit. Balliere, Tindall & Cox, London, 1938.
Mandoul, R. (1939). Annales de parasit. humane et compares. T. XVII, No. 3, pp. 187-192. Abst. Rec. de med. vet. d'Alfort. (1942) 118 : 137.
Foster, A. 0. Keeping Livestock Healthy. United States Departmcnt of Agriculture, 1942. Washington.