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Rattlesnake Vaccine


Rattlesnake Vaccine

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.