Rattlesnake Envenomation

Snakes

RATTLESNAKES

A FACT OF LIFE IN THE DESERT

Arizona is home to 13 of the 36 identified species of rattlesnakes, more than any other state.  The Western Diamondback is the most common of these and attains the largest size.  It can attain a length of over  5 ½ feet  and is responsible for more bites to humans than any other rattlesnake species in the U.S.  In Arizona, rattlesnakes usually come out of their winter dens in March or April, when the temperatures are approaching 80 degrees and remain active until October. During the summer, they are most active at night. Their natural diet consists of mice, rats, gophers, frogs, small birds and occasionally large insects.

Rattlesnakes are classified as “pit vipers” because of their “loreal pit,” a heat-sensing organ between the nostril and eye, which is used to locate prey and potential predators. They can be recognized from a distance by the triangular shape of the head with a noticeable neck, cat like pupils, and, of course, the “rattle” at the end of the tail. But, don’t rely on seeing or hearing the rattle to identify them. Rattlesnakes don’t always rattle before striking. If you see one, do not approach it, even if it’s not coiled. It isn’t necessary for a rattlesnake to be coiled in order to strike, although it does allow them to strike from a greater distance.

The venom of a pit viper is derived from modified salivary glands and is injected through the hollow retractable fangs. The purpose of the venom is not to kill, but to immobilize the prey and predigest its tissues. Rattlesnake venom has multiple actions on the body, including damage to the walls of the blood vessels, local tissue death, a decrease in the ability of the blood to clot, and nervous system dysfunction. Within 30 minutes to an hour of a venomous bite, there is usually local pain, swelling, and bruising, and sometimes excessive bleeding. Then there are cardiovascular effects. The blood vessels dilate, lowering the blood pressure and causing the patient to go into shock. The heart compensates by beating more rapidly than normal and arrhythmias can also occur because of the effect of the toxins on the heart muscle.

Less than 1% of human rattlesnake bites result in death, but death is more common in dogs due to their smaller size.  The snake is able to control the amount of venom injected and that amount is based on the snake’s perception of the situation. Dogs are more often bit on the head or face and those bites are very serious due to the close proximity of major blood vessels.  On the basis of the amount of venom per pound, cats are more resistant, but often antagonize the snake by playing with it. About 20-25% of bites to humans from adult pit vipers are “dry bites” in which no venom is injected.  Unfortunately, there is no way to determine how much venom has been injected at the time the bite occurs, so all rattlesnake bites should be considered an emergency!

There is a vaccine available for dogs that can decrease the severity of injury when a dog is bitten. It is manufactured by Red Rock Biologics and contains inactivated components of the venom of the Western Diamondback rattlesnake (Crotalus atrox), but may provide some cross protection against other types of rattlesnakes and Copperheads. After the initial vaccination, a booster must be given in 1 month for maximum protection. Then a booster is given every 6 to 12 months.  The vaccine is indicated for dogs that are likely to encounter rattlesnakes and/or could be far from medical help if bitten. The vaccine does not eliminate the need for medical treatment if your dog has been bitten by a snake. It also doesn’t provide protection against the Mojave or Eastern Diamondback rattlesnake, cottonmouth snakes, or coral snakes.

So, you might ask “What should I do if my pet is bitten by a rattlesnake?”  The first thing to do is get away from the snake.  Many people are bitten in the process of trying to kill the snake. An agitated snake is very dangerous! Remove your pet’s collar and try to keep the pet calm. Carry your pet, if necessary. Do not give any medications, apply ice, heat, or a tourniquet, or cut into the bite to remove the venom.  Call your veterinarian as soon as possible, even if the pet has received a rattlesnake vaccine, and immediately transport the pet for medical treatment.  DO NOT WAIT!  Be sure to tell your veterinarian if the pet has received antivenin previously to treat a snake bite.

The mainstays of treatment for snake envenomation are pain control, cardiovascular support and administration of antivenin. Upon arrival at the hospital, a blood sample and, if possible a urine sample will be collected from your pet. Areas of local swelling will be measured and an IV catheter will be placed in a vein to administer fluids, medications, and possibly antivenin.  Antivenin is a product that is produced by injecting a horse with small amounts of rattlesnake venom to induce an immune response. Serum, which contains neutralizing antibodies, is harvested from the blood of the horse to produce the product.  Because of the process used to produce antivenin and because of its fragile nature, it is an expensive product. However, administration of antivenin is the only proven specific treatment against pit viper envenomation. Ideally, it is given as early as possible to prevent further tissue damage and reverse the impairment of blood clotting.  You should expect your pet to be hospitalized and monitored closely for at least 8 hours, and usually longer, after receiving a snake bite.

The best way to prevent snake bite injury is avoidance. If you see a rattlesnake, leave it alone and calmly walk away from it. It will not attack or bite unless provoked.  Always keep your dog close to you when hiking so you can lead the dog away from danger, as well. It is a good idea to carry a walking stick to tap the ground ahead of you and rustle the vegetation.  Snakes will avoid you if they hear you coming. Don’t allow your pets to wander into areas with tall grass or shrubs where snakes are more likely to be hiding. Consider enrolling your dog in a rattlesnake avoidance class to counteract the normal curiosity dogs have about snakes.  At home, you should keep the grass cut short, keep yard waste picked up, and control rodents. If you have a wall or fence, keep the vegetation around it short, so snakes can’t go over the barrier and cover any holes or openings.

We sincerely hope that you and your pet can avoid any adverse encounters with the local rattlesnakes. If you have any questions specific to your pet regarding the treatment or prevention of rattlesnake bites or appropriate use of the rattlesnake vaccine, please contact us at (480) 451-8375 or practicemanager@kcanimalhospital.com.

 

 

REFERENCES:

Identification of Arizona rattlesnakes:

http://www.azgfd.gov/w_c/arizona-rattlesnakes.shtml

Snake avoidance training for dogs:

http://www.partnersdogtraining.com/snakeproofing.html

Information about the rattlesnake vaccine for dogs:

http://www.redrockbiologics.com/rattlesnake_vaccine_for_dogs.php

 

 

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