Page 268 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

Cardiovascular Toxicity Chapter | 14 235

VetBooks.ir increased heart rate, increased blood pressure, and quinquestriatus) includes chlorotoxin, which blocks small
conductance chloride channels.
tachycardia. Autopsies on dogs revealed hemorrhage of the
for
scorpion
symptomatic.
Treatment
sting
is
heart (Hayes and Laws, 1990). There is no antidote to
metaldehyde poisoning. Symptomatic therapy includes Hypertensive symptoms are treated with vasodilators.
gastric lavage with sodium bicarbonate and medication to Scorpion antivenoms are available. Insulin administration
control seizures. controls effects caused by catecholamines upon scorpion
envenomation.
MYCOTOXINS
HYMENOPTERA
Of the several thousand species of mushrooms
Members of the order hymenoptera include apoidea
(Basidiomycete fungi), less than 100 are toxic. Often
(bees), vespoidea (wasps, hornets, and yellow jackets),
mixed into feed, or ingested by pets, the toxic principle is
and formicidae (ants). Their injected venom is poisonous.
primarily the presence of amatoxins (bicyclic octapep-
A lethal dose is approximately 20 stings/kg in most mam-
tides) (Berger and Guss, 2005). Amatoxin inactivates
mals (Fitzgerald and Flood, 2006). The severity of the
RNA polymerase II in cell nuclei and DNA transcription,
stings is increased by anaphylactic reactions.
thus preventing protein synthesis, curtailing cell metabo-
Stings can cause myocardial infarction and myocardi-
lism (Duffy, 2008; Chang, 2009).
tis. Increases in serum enzyme levels and necrosis in the
Amatoxin signature on cardiac tissue shows small hem-
myocardium have been reported (Levine, 1976; Ferreira
orrhage, cloudy swelling, and degeneration. Elevation of
et al., 1995). Mast cells in cardiac tissue may be affected
cardiac enzymes (Unverir et al., 2007), including CK-MB
by their mediators that have cardiotoxic effects, including
isoenzyme and myoglobin, is noted. The LD 50 is
arrythmogenesis. Wasp stings can cause Mobitz Type I
0.1 0.3 mg/kg b.w. for most mammals. A difference in
heart block and myocardial infarction (Wagdi et al., 1994).
intraperitoneal and intravenous injection values is notewor-
ECG changes, myocardial necrosis, and arrest of cardiac
thy. Also, α-amanitin LD 50 is 0.1 mg/kg b.w. for rats, while
beats were noted after envenomation by Africanized hon-
amanullin, also an amatoxin, has an LD 50 in mice of 20 mg/
eybee venom in Wistar rats. A honeybee sting can produce
kg b.w. and is nontoxic to humans. Low calcium and phos-
significant elevations of the ST-segment, CK-MB activity,
phate levels as well as varying levels of the hormones that
and troponin I and T levels.
control their metabolism have been noted. Heart block and
Treatment includes antihistamines, steroids, broncho-
bradycardia have been observed. Also, sinus tachycardia
dilators, and alpha- and beta-receptor agonists.
and hypotension are typical cardiac clinical symptoms.
In dogs, electrolyte abnormalities and bradyarrhythmia
(SA exit block and sinus arrest) symptoms reminiscent of OPHIDIAN
muscarinic intoxication were noted and relieved by atro-
The 600 known venomous snakes belong to the following
pine (Lee et al., 2009). Treatment aims at minimizing
four families: Atractaspideae, Colubrideae, Elapideae,
amatoxin absorption, administering activated charcoal,
and Viperideae. The Crotalideae is a subfamily of
and hydration maintenance.
Viperideae and includes pit vipers, the moccasins, and rat-
tlesnakes, while coral snakes belong to the Elapideae.
Snake venom contains biologically active ingredients
ANCILLARY CAUSES OF CARDIAC
with cytotoxic, neurotoxic, and coagulant effects. From
TOXICITY the cardiac system point of view, the phosphodiestrases
that lower blood pressure and phospholipase A2 that
Anthropods
causes hemolysis are most significant.
Envenomenation by arthropods (scorpions and spiders) is Subcutaneous LD 50 of cottonmouth (Agkistrodon pisci-
a serious health concern to humans and animals in many vorus) venom is 25.8 mg/kg b.w., for Vipera berus the LD 50
countries (Murthy et al., 1999). In dogs and rabbits, is 6.45 mg/kg, and for Vipera latifii is 4.61 mg/kg b.w.
3.5 mg/kg b.w. of scorpion venom causes an increase in Disruption of the normal blood clotting pathways is
LDH and CK-MB enzyme levels. ECG changes in T significant. Some prevent clot formation and induce hem-
waves (biphasic) and ST-segment and alternans indicate orrhagic shock. Other toxins induce clotting, causing
myocardial damage, ancillary arrhythmias, conduction stroke and heart attacks by blocking blood flow.
defects, and infarction-like patterns (Gueron et al., 1992; Cardiotoxins bind to muscle cells causing depolariza-
Bentur et al., 2003). Scorpion toxin includes tion and prevention of muscle contraction, thus interfering
potassium channel blocking peptides (Kumar et al., with the rhythmicity of the heart. Snake bites usually are
2011). The venom of the deathstalker scorpion (Leiurus noted in dogs bitten on the head or neck. In one particular