Venomous Snakes

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.

The Western Rattlesnake

The Western Rattlesnake (Crotalus viridis ) – This snake species has been divided up into numerous subspecies and DNA analysis is showing that these may actually be separate species. There are currently 7 subtypes of Crotalus viridis:

                Southern Pacific Rattlesnake (Crotalus viridis helleri)

                Great Basin Rattlesnake (Crotalus viridis lutosus)

                Northern Pacific Rattlesnake (Crotalus viridis oreganos)

                Western Diamondback (Crotalus atrox)

                Red Diamondback (Crotalus ruber)

                Sidewinder (Crotalus cerastes)

                Speckled Rattlesnake (Crotalus mitchellii)

                Mojave Rattlesnake (Crotalus scutalatus)

 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 t heir faces between the eye and nostril. The pits help them locate prey.

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.

An exception would be the Mojave rattlesnake whose venom is “neurotoxic.”  The bite of this snake causes rapid paralysis. This includes paralysis of the respiratory muscles and suffocation.

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 (at least $100-$200 per vial) and a large dog with a severe bite is likely to require several vials. Because the product if 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 $700 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.

A separate antivenin is available for coral snake venom.

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

Recently, Red Rock Biologics has released  a vaccination against the venom of the Western Diamondback (Crotalus atrox). This vaccine also protects against the venom of six out of seven of the other California rattlesnakes. Testing on the venom of the Mojave rattlesnake is still pending.

Hiking dogs and dogs that live in rattlesnake areas are good candidates for this product. The vaccine is administered in two doses 2-4 weeks apart and then annually thereafter.

 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.

Content taken from Rattlesnake Bites in California, By Wendy C. Brooks, DVM, DipABVP. Educational Director, VeterinaryPartner.com. Published 8/23/2004 .

Red Rock Biologics Rattlesnake Vaccine

(Crotalus Atrox Toxoid)

The rational for vaccination against snakebite is to use the dog’s own immune system to generate antibodies which will reduce the effective dose of venom that reaches circulation.

On average, vaccinates have 3-4 vial equivalents of antivenom circulating by one month after the second dose of vaccine. Upon envenomation, vaccinates will require less antivenom than nonvaccinates.

Because the preformed antibody is present at the time of the bite, expect significant reductions in tissue damage as the antibody ties up venom components at the bite site.

Vaccinated animals experience less pain, less swelling, and less tissue destruction than an unvaccinated animal given the same dose of venom.

Even with the vaccine, snakebite remains a veterinary emergency. Antibiotics to combat infection are an essential part of snakebite treatment.

Concluding Remarks

Club members who enjoy having their dogs with them in our Arizona outdoors should carefully consider and prepare for rattlesnake encounters. Its their Arizona also.

The first level of preparation should be to have your dogs snake avoidance trained. No dogs’ training is complete until they will avoid the sight, the smell, and the sound of a rattlesnake. This is their foundation for survival.

Secondarily, vaccination protection against unexpected envenomation is now possible.  Red Rock Biologics appears to be first to market with such a vaccine. Before taking this step, consult with your veterinarian.

And always consider and respond to rattlesnake bite as a medical emergency. Leave the field and seek veterinary help as quickly as possible.  Your little friend’s welfare and possible survival will depend on the action you take.