Page 830 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

788 SECTION | XII Poisonous and Venomous Organisms

VetBooks.ir alpacas and emus (Stair and Plumlee, 2004; Simpson
et al., 2013). Poisoning in human beings has been noted
for decades and is usually the result of either improper
medicinal use of cantharides or malicious poisoning
(Krinsky, 2002). Horses are particularly susceptible to the
effects of cantharidin (Stair and Plumlee, 2004). The esti-
mated lethal dosage of cantharidin for the horse is approx-
imately 0.5 1 mg/kg, and as little as 4 g of dried beetles
may be lethal to a horse (Krinsky, 2002). The oral experi-
mental lethal dosage of crystalline cantharidin for dogs
and cats was 1.0 1.5 mg/kg, and it was 20 mg/kg for rab-
bits. It is estimated that the lethal dosage for a human is
less than 1.0 mg/kg.
Cantharidin produces an intense, direct irritant effect
on the skin and the mucous membranes of the esophagus,
stomach, and intestines. Once absorbed, the toxin may
FIGURE 58.1 An adult striped blister beetle (Epicauta vittata). Photo
courtesy of James E. Appleby, University of Illinois. affect many different organs. Excretion is via the kidneys,
resulting in transfer of the irritant effect to the urinary
tract, particularly the bladder and urethra (Krinsky, 2002).
Clinical signs vary with the dose ingested. Massive
doses may cause shock and death within 4 h (Krinsky,
2002). Smaller doses may cause gastroenteritis, nephrosis,
cystitis, and/or urethritis; thus, signs may include
anorexia, soft feces, mucoid to bloody feces, intestinal
atony, colic, dysuria (frequent, painful urination, or oli-
guria to anuria), and hematuria. The body temperature

may elevate to 106 F (41.1 C). Other signs observed

include depression, weakness, muscle rigidity, collapse,
prostration, dehydration, and sweating (Krinsky, 2002).
Animals frequently become dyspneic, and rales may be
detected on auscultation due to pulmonary edema.
Myocarditis may initiate cardiovascular signs including
FIGURE 58.2 An adult blister beetle (Epicauta), with hemolymph dro- tachycardia, congested mucous membranes, and decreased
plets containing cantharidin. Photo courtesy of Dr. Maria Eisner, capillary refill time. Synchronous diaphragmatic flutter
Cornell University.
and muscle fasciculations have been reported in horses
and are thought to be the results of hypocalcemia (Stair
doses to livestock that feed on forage when it is used as and Plumlee, 2004). Ulceration of the oral mucosa mem-
hay. Modern methods of hay harvesting, especially crimp- branes may be observed, and animals may be seen dip-
ing, decrease the opportunity of blister beetles to vacate ping their muzzles into water without drinking (Krinsky,
the foliage before it is incorporated into hay, thereby 2002). Diarrhea may be observed in animals that live for
increasing the likelihood of blister beetles being trapped a few days. The course of the disease may be as short as
in the hay (Stair and Plumlee, 2004). Cantharidin released 4 h, with massive dose ingestion, to 5 days in lethal poi-
from crushed adult blister beetles may contaminate hay soning. In horses, the mortality rate is approximately
without visual evidence of insect parts. Cantharidin is 50%, with horses surviving more than 1 week having a
very stable and may persist in hay for long periods of favorable prognosis (Krinsky, 2002).
time. Because in the United States alfalfa is most widely During intoxication, dehydration and shock cause eleva-
grown in the South, cantharidin toxicosis is most com- tions in serum protein and packed cell volume (Stair and
monly found in the southern states; however, due to inter- Plumlee, 2004). The damaged gastrointestinal mucosa allows
state transport of alfalfa hay throughout the country, rapid invasion of enteric bacteria, resulting in bacteremia
cantharidin toxicosis can occur in any state. and leukocytosis. There may be mild elevation in serum
Horses are the species in which cantharidin toxicosis urea nitrogen. Profound hypocalcemia (5.9 mg/dL; normal,
is most commonly reported. However, the following hosts 12.86 1.2 mg/dL) and hypomagnesemia (0.7 1.8 mg/dL;
have also been poisoned in natural or experimental situa- normal, 2.56 0.3 mg/dL) have been reported. Specific grav-
tions: cattle, sheep, goats, rabbits, rats, hedgehogs, dogs, ity of urine is low in the early stages of the disease, and