Page 982 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Urinary system 957

VetBooks.ir adult animals. Laparoscopic procedures in stand- hay. Outbreaks can occur elsewhere mainly due
Uroperitoneum should be managed similarly in
to shipment of contaminated alfalfa hay from mid-
ing horses have reported good outcomes. Significant
urine leakage from the ureters or kidneys is difficult western USA. Cantharidin is a potent vesicant and
irritant. When absorbed in the epithelial cells it
to manage in horses. If the defect persists, nephrec- causes oxidative stress and DNA damage, which
tomy should be considered. stimulates the release of serine proteases. Proteases
cause disintegration of desmosomes and leads to
Prognosis detachment of the tonofilaments that hold cells
The prognosis for recovery in foals is usually together. There is loss of cellular connections (acan-
good. Concomitant infection or sepsis significantly tholysis), vesicle formation and ultimately epithelial
decreases the chance for a favourable outcome. In blistering. In addition, the inhibition of protein phos-
adults, or in cases of urine leakage from the kidney phatases 1 and 2A causes a disruption in the renal
or ureters, the prognosis is less favourable. energy, electrolyte and water metabolism, vasocon-
striction and endothelial cell leakage. All these lead
CANTHARIDIN TOXICOSIS to acute renal tubular necrosis, renal injury and hae-
(BLISTER BEETLE TOXICOSIS) maturia. Haemodynamic changes due to generalised
disease may contribute to the renal damage.
Definition/overview
Cantharidin is a highly irritable substance that Clinical presentation
causes acantholysis and vesicle formation when in Typical clinical signs are those referable to shock,
contact with skin or mucous membranes. The com- GI and urinary tract irritation, renal insufficiency,
pound is contained in beetles belonging to the fam- myocardial failure and hypocalcaemia. Extensive
ily Meloidae. Different species of blister beetles are inflammation in the urinary tract, haemorrhage and
found from southern Canada to Mexico, and from pseudo-membrane formation are associated with
the Atlantic coast to Utah, Texas and New Mexico. stranguria, pollakiuria and haematuria. In some cases,
Even though there are approximately 2,500 known sudden death with few prodromal signs may occur.
species of blister beetle worldwide, cantharidin toxi-
cosis is a common event only in the USA. Differential diagnosis
Differential diagnoses include cystitis, pyelone-
Aetiology/pathophysiology phritis, urolithiasis, renal failure, neoplasia, bladder
Cantharidin toxicosis occurs when horses ingest paralysis, NSAID toxicity and mercury toxicosis.
food contaminated with blister beetles (Epicauta
spp.) (Fig. 7.45). The most common source is alfalfa Diagnosis
Concurrent signs of urinary tract and GI disease,
particularly severe mucosal irritation, are suggestive
of cantharidin toxicosis. Hay should be examined for
7.45
the presence of blister beetles, although the failure to
identify beetles does not eliminate the possibility of
cantharidin toxicosis. The urine SG is low (isosthe-
nuria) even in the face of dehydration. Macroscopic
haematuria is usually present. Epithelial cells are
occasionally seen in the urine, but casts are rarely
present.
Blood analysis commonly reveals hypocalcaemia,
hypomagnesaemia, hypoproteinaemia and mild azo-
taemia. Chemical analysis for cantharidin is accom-
Fig. 7.45 Epicauta spp. (Photo courtesy T Trilar) plished by evaluation of urine or stomach contents.