Page 814 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Gastrointestinal system: 4.2 The lower gastrointestinal tr act 789

VetBooks.ir distension with decreased intestinal motility will be Aetiology/pathophysiology
Cantharidin is found in a variety of blister beetles,
evident.
tles are found over much of the USA, particularly
Stricture of the pelvic flexure or small colon particularly those of the Epicauta species. These bee-
An impaction at the level of the pelvic flexure or in the southwestern part of the country. Horses are
the small colon is often palpable p/r. Gaseous dis- usually exposed via ingestion of alfalfa hay contain-
tension of the large intestine and, possibly, the ing dead beetles that were trapped in the hay dur-
small intestine may be present if the obstruction ing harvesting. Simultaneous cutting and crimping
is severe. In some cases, narrowing of the lumen of forage may increase the chance of blister beetle
may be felt. contamination. Blister beetles tend to live in clus-
ters and are usually not evenly distributed between
Regardless of the location, exploratory surgery is or within bales of hay from the same cutting. The
often required to definitively identify the stricture. concentration of cantharidin in beetles can be vari-
able. Ingestion of as little as 4–6 g of dried blister
Management beetle may be fatal.
Duodenal stricture Cantharidin is very irritating to mucous mem-
Surgery is required. If the stricture is distal to the branes and skin, causing acantholysis and vesicle
opening of the hepatopancreatic ampulla, a duode- formation. Sloughing of the GI mucosa may occur
nojejunostomy to bypass the lesion and a jejunoje- following ingestion, particularly in proximal regions.
junostomy to avoid stagnation of intestinal content Compromise of the intestinal mucosa may result
are needed. Pyloric stenosis can be corrected by in fluid loss, protein loss, alteration of electrolyte
performing a side-to-side gastroduodenostomy. homeostasis and absorption of bacterial toxins nor-
mally excluded by the mucosal barrier. Dehydration,
Ileal stricture hypovolaemic shock, toxaemia and abdominal pain
Surgical treatment is required. An ileocaecal bypass may rapidly develop. Renal tubular necrosis may
is performed with or without resection of the ileum. also develop. Ulceration of the renal pelvis, ureters
and bladder mucosa is common. Cardiac toxicity is
Stricture at the level of the pelvic flexure or less common but may occur and is characterised by
small colon ventricular myocardial necrosis and pericardial effu-
Some strictures, such as a pelvic flexure, may be cor- sion. Hypocalcaemia develops for unknown reasons.
rected surgically by a longitudinal incision closed
transversally if the stricture is not severe. In the Clinical presentation
remaining cases, resection and anastomosis of the Clinical signs may be apparent hours to days fol-
affected segment are needed. lowing cantharidin ingestion. The severity of clini-
cal signs is dose dependent. GI, urinary, cardiac and
Prognosis systemic signs may be apparent. Abdominal pain,
The prognosis is fair to poor for duodenal stricture, anorexia, depression, sweating and frequent drinking
good to fair for other locations. or soaking the muzzle in water are most commonly
observed. Oral mucous membranes are hyperae-
CANTHARIDIN TOXICOSIS mic, with a prolonged capillary refill time (CRT).
(BLISTER BEETLE TOXICOSIS) Oral ulceration is uncommonly observed. Profuse
salivation is sometimes present. Body temperature,
Definition/overview heart rate and respiratory rate are usually elevated.
Cantharidin is a highly irritating toxin that can If myocardial damage is present, heart rhythm may
cause GI, urogenital and cardiac damage following be abnormal. Pollakiuria and stranguria may be
ingestion. observed, with grossly evident haematuria present
later in the disease. Synchronous diaphragmatic