A venomous animal is one with specialized glands that secrete a
toxic substance which immobilizes and then kills prey. Spiders,
insects, and snakes are venomous animals with snakes being
particularly deadly.
There are five types of venomous snakes:
• Colubridae – These snakes possess rigid rear fangs
in their mouths. An example would be the boomslang (an African tree
snake)
• Elapidae – These snakes possess rigid front fangs
in their mouths. Examples would be the cobra, mamba, and coral
snake.
• Viperidae – These snakes have hinged front fangs.
The adder and asp are examples.
• Crotalines – These snakes also have hinged front
fangs and are the subject of our discussion. These include the
copperheads and rattlesnakes.
• Hydrophiidae – These have rigid front fangs and are
completely aquatic. These are the sea snakes.
The snakes with rigid fangs bite and hold their prey until it dies.
The snakes with hinged fangs, such as the rattlers, will strike,
release the prey, and then look for the dead body.
Snake venom is highly complicated. At least 26 separate enzymes
have been identified but some 10 enzymes appear common to all snake
venoms (though in different concentrations). All snake bites are
not equal. The quality of venom depends not only on the type of
snake but on the season, the geographical region, the age of the
snake, and how recently it has released venom previously.
Rattlesnakes
The physical appearance of each snake species is variable and it is
difficult to tell what species of snake one is looking at. Some
general principles in distinguishing poisonous snakes are:
• Broad, triangular head with a noticeable “neck” behind the
head.
• Vertical pupils (non-poisonous snakes have round pupils)
though hopefully one would not be close enough to evaluate
this.
• The Crotalines are also called “pit vipers” because they
have heat-sensing “pits” on their faces between the eye and
nostril. The pits help them locate prey.
Rattlesnakes can be found in rural areas as well as suburban areas
where there is sufficient natural habitat. These snakes will
hibernate during cold months and are active during the warm
months.
Dogs vs. Snakes
Dogs encounter snakes during play or work in the snake’s natural
habitat. Most bites to dogs occur on the face or extremities. The
rattlesnake bite is generally hemotoxic, which means that it exerts
its toxin by disrupting the integrity of the blood vessels. The
swelling is often dramatic with up to 1/3 of the total blood
circulation being lost into the tissues in a matter of hours. The
toxin further disrupts normal blood clotting mechanisms leading to
uncontrolled bleeding. This kind of blood loss induces shock and
finally death. Facial bites are often more lethal as the swelling
may occlude the throat or impair ability to breathe.
Treatment
The faster the bite is recognized, the more effective the treatment
is. Do not try to cut the bite wound open or suck out the poison.
Seek veterinary care immediately for proper treatment.
IV Fluids
Since the most common mechanism of death from rattlesnake bite is
circulatory collapse, IV support and monitoring for signs of blood
pressure drop are very important. Fluids may be started at a
relatively slow rate if the patient is stable but should signs of
impending trouble occur, circulatory volume replacement is as easy
as opening a drip set valve. Twenty four hours of observation
post-bite is a prudent observation time with IV fluid
administration all the while.
Antivenin
There are numerous misconceptions about antivenin. The first is
simply the name of the product. It is not “anti-venom.” It is not a
single injection that provides the antidote to snake bite
venom. Antivenin is a biological product consisting of
antibodies made by horses in response to exposure to four common
Crotaline venoms. The antibody serum is reconstituted into an
intravenous drip that is run into the patient over at least 30
minutes or so.
Antivenin is expensive (up to $500 per vial) and a large dog with a
severe bite is likely to require several vials. Because the product
is of horse origin, often a scratch test to the ear flap is used to
test for immunological sensitivity (i.e. to predict whether the
patient is likely to have anaphylactic reaction to the antivenin
once it is administered intravenously. The patient will likely
always be sensitive to equine products after administration of
antivenin which makes future snake bite treatment problematic.
A newer, more purified antivenin of sheep origin has recently been
marketed (“Cro-Fab” antivenin) but this is even more expensive
(approximately $900 per vial).
Antivenin is very helpful in the inactivation of snake venom but
there is a narrow window during which it must be used. After about
4 hours post-bite, antivenin is of minimal use.
Antihistamines
Injections of antihistamines may or may not be helpful with the
inflammation from the actual snake bite but may be helpful in
warding off anaphylactic reaction to the antivenin. Further, the
sedating side effects of antihistamines help calm the patient.
Antihistamine use is a common therapy used in the treatment of
snake bites.
Corticosteroids seem like they would be helpful as they are
universally anti-inflammatory; however, their use has been
associated with higher mortality rates so they are not generally
administered.
Other Treatments
Blood transfusion may be necessary if life-threatening blood loss
has occurred. Antibiotics are often used to control secondary
infections. Medications to control pain are important to snake bite
patients.
Vaccination
Red Rock Biologics of California produces a vaccination against the
venom of the Western Diamondback (Crotalus atrox). This
vaccine protects against the venom of the other rattlesnakes and
has proven to be very effective in reducing both mortality and
morbidity after a rattlesnake bite. The vaccine has recently been
released for use outside of the state of California.
Hiking dogs and dogs that live in rattlesnake areas are good
candidates for this product. The vaccine is administered in two
doses 2 to 4 weeks apart and then annually thereafter. Vaccinated
dogs still must receive treatment after a bite, but its chance of
survival is tremendously increased.
A snake bite should always be treated as an emergency, even
in a vaccinated dog.
If your dog is bitten by a rattlesnake, seek veterinary attention
immediately.
More
Questions & Answers About Rattlesnake
Vaccine
Vaccine Manufacturer
Web Site
The FDA has a rattlesnake bite
prevention page for humans at http://www.fda.gov/fdac/features/995_snakes.html
Call our office for more information on vaccinating
your dog against rattlesnake bites.
