From AzVDL:
BLISTER BEETLE POISONING IN HORSES
Arizona horse owners and veterinarians should be aware that three horses
in
the Benson, Arizona area have died and two more are re****ted to be sick as
a
result of consuming a batch of locally-grown baled alfalfa hay found to be
contaminated with blister beetles (Epicauta sp.). One of the three horses
died in 24 hours and two more died the next day. All were fed from the
same
bale of a new lot of second-cutting alfalfa on Friday, (07/02/04) evening
and were ill and refused to eat the next morning. Personnel in the AZVDL
toxicology section subsequently examined the alfalfa hay consumed by the
horses and found blister beetles. Clinical signs that were re****ted by the
owner and submitting veterinarian were typical of blister beetle poisoning
and included: depression, shaking, refusal to eat, "toxic" mucous
membranes,
diarrhea, colic with sweating, and immersion of the muzzle and playing
with
the water as though the horses were attempting to flush their mouths.
Straining to urinate was also observed in some and one horse was observed
to
void bloody urine. The hay grower has voluntarily recalled all lots of hay
from the cutting.
Blister beetle (cantharidin) poisoning occurs most often in horses but may
also occur in cattle, sheep, and goats. Poisoning is associated with the
consumption of alfalfa hay contaminated by blister beetles (Epicauta sp.).
Swarms of blister beetles commonly congregate around hay fields to feed on
pollen and plant nectar and to mate. Modern harvesting practices where hay
fields are swathed and crimped in one pass create a greater risk by
killing
beetles infesting the hay, which then contaminate hay bales. Because
blister
beetles tend to swarm their concentrations in hay can be highly variable.
Many bales may have no beetles present while only a few bales may have
significant numbers. Dead beetles inadvertently consumed by a horse in its
hay are extremely toxic. Accidental consumption of only a few dead beetles
will poison a horse. The beetles contain the toxin cantharidin, which is
thought to protect the insects from their natural predators. Cantharidin
is
a terpenoid compound that is a strong vesicant that is extremely
irritating
to skin and mucous membranes and is rapidly absorbed and eliminated in the
urine. Severe damage to the oral and gastrointestinal mucous membranes,
urinary tract, and other organs occurs and in severely poisoned horses
shock
and death can occur within a few hours. The severity of poisoning is
dose-related and less-severely-affected animals can be treated
successfully.
There is some uncertainty whether residual effects occur in horses that
survive poisoning; however, given the fact that the toxin has effects on
many organ systems surviving horses should be monitored closely.
A diagnosis of blister beetle poisoning is suggested by (1) compatible
clinical signs and a history of alfalfa hay consumption and (2) finding
blister beetles in the hay or in the bottom of the feed bunk. Confirmation
of the diagnosis can be made by chemical analysis of urine, serum, or
stomach contents for cantharidin. Clinical signs vary with the severity of
poisoning but suggestive ones include: colic, sweating, feed refusal,
salivation, congested oral mucous membranes, ulceration of the oral
mucosa,
wa****ng the muzzle in water, straining to urinate, blood in the urine,
elevated body temperature, diarrhea, abnormal heart rate and respiration,
fever, and muscle stiffness with short-strided or "goose-stepping" gait.
Horses showing neuromuscular signs may have abnormal serum calcium and
magnesium levels, which will require correction. Laminitis has been
re****ted
to occur in some equine cases.
Animals suspected of having Blister beetle poisoning should be seen on an
emergency basis by an equine veterinarian. Severely affected animals may
require hospitalization because of the intensive treatment required. There
is no specific antidote for blister beetle poisoning but prompt treatment
and reducing absorption of the toxin can sometimes salvage affected
horses.
Appropriate doses of activated charcoal followed by mineral oil two to
three
hours later have been recommended. Fluid therapy is usually necessary as
are
analgesics for pain control. Clinical signs and serum electrolytes should
be
monitored closely and treatment adjusted as necessary to correct any
deficits and neuromuscular signs. Gastrointestinal protectants are also
suggested in cases where there is persistent feed refusal and water
playing.
Broad-spectrum antibiotics are also recommended. However, amino
glycoside-type drugs are contraindicated. The prognosis varies with the
amount of toxin ingested but survival of horses for two to three days has
been re****ted to be associated with a more favorable prognosis and
outcome.
A photo of crushed blister beetles contaminating hay in this case
accompanies this Animal Health Alert. Readers should realize that the
appearances of the many species of this insect vary. Hay containing
beetles
of uncertain identity should be considered suspect, withheld from use as
feed, and the beetles submitted to the AZVDL for identification.
T. H. Noon, DVM
AZVDL Toxicology and Nutritional Testing Section
S. Peder Cuneo , DVM, MS
Extension Veterinarian
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