Hyperbaric chamber

A dog is placed into a Hyperbaric Oxygen Therapy chamber to illustrate how it works.

Snake bites are a common and sometimes serious medical cases at our emergency animal hospitals. The best outcomes are achieved if treatment is early and aggressive, and in most cases the prognosis is good. Bites from rattlesnake species are generally more serious, and the antivenin used to treat them may provide only partial protection from the effects of their venom, which emphasizes the importance of avoiding contact between your pet and these snakes.

The advent of warm weather brings many dogs into contact with snakes. We live in a state that has the dubious distinction of hosting every species of venomous snake in North America. The vipers include the copperhead, cottonmouth, as well as the canebrake, diamondback and pigmy or pygmy rattlesnakes. The Elapidae family is represented by the elusive yet highly venomous coral snake.

That said, the phobia surrounding snakes is totally disproportionate to the actual threat that snakes, even venomous ones, pose. Rattlesnakes do not want to bite you. That’s why they have rattles, which should warn you to give them some space. Cottonmouths, contrary to popular campfire tales, do not chase you. They flare their big white mouth to scare you away. They know you are 200 times their size, and there is nothing to be gained by contacting you. Copperheads, the ones you will be most likely to encounter, are non-aggressive, and generally only bite in response to being attacked or accidentally stepped on.

Copperhead bites are common, but like all snake bites, they generally occur because the dog attacked them, not the other way around. These bites are generally not fatal, but can cause severe pain, swelling and local tissue damage. Cottonmouth bites are worse, but again, generally not fatal. The size of the snake relative to the dog, the location of the bite, the number of bites, and how effectively the venom is delivered, are the variables that determine how serious a bite will be.

To minimize the damage to tissues and reduce the likelihood of a fatal outcome, these bites should be treated immediately. We recommend the use of antivenin, fluid support and antibiotics.

The use of Hyperbaric Oxygen Therapy at our Mount Pleasant facility has made a major difference in the treatment of these cases by minimizing pain, swelling, tissue death and scarring. Time is of the essence in limiting harm and optimizing outcomes, but survival is likely following bites from these types of snakes. Encounters with their larger cousins are not as assured to end well.

The canebrake or timber rattlesnake is one of the most common rattlers in our area. The eastern diamondback is equally dangerous but is very rare. The pygmy rattler, while not as venomous as either of these, can still deliver a painful, though seldom lethal bite.

The venom of all rattlers contains cytotoxins. These are toxic to cells and are responsible for tissue necrosis (death). There are other biotoxins that are damaging to the liver, heart , kidneys, etc. But all rattlesnakes also have some neurotoxin in their venom. Canebrake rattlesnakes vary widely in the composition of their venom and some can be strongly neurotoxic, affecting the nerves or nervous tissue. This is a problem for treating these bites in humans and dogs.

Antivenin is made by injecting a horse or a sheep with the venom of various snakes. Not enough is given to kill them, but they will form antibodies to the venom. The antibodies are then collected from their blood and stored as a powder. When someone is bitten by a snake the antibodies (antivenin) are given, which intercept the venom before it can cause harm. Antivenin for humans is made from the eastern and western diamondback, and Mojave rattlesnakes, and the cottonmouth. Antivenin for dogs is made from the eastern and western diamondback, South American rattlesnakes, and the fer-de-lance, a highly venomous pit viper species.

According to Dr. Jay Madey, who was a neurology resident at MUSC when he treated a Summerville boy for a nearly fatal canebrake rattler bite, this snake's neurotoxin is complex and the antivenins in our arsenal may have little effect on them. He explained to me (Henri Bianucci) that the human approved antivenin does not have antibodies to the canebrake venom and that the antibodies to other snake venoms may not offer protection to the neurotoxic component of canebrake venom. This is what was nearly fatal for the Summerville boy, and has claimed a number of dogs that we have seen over the years. He said that the human antivenin worked beautifully against the tissue-destructive elements of the venom, but did not seem to touch the neurotoxin.

This has been our experience as well. That’s why dogs with cottonmouth and copperhead bites, when treated quickly with antivenin, tend to recover quickly with minimal tissue damage. However, with rattlesnake bites, we have seen the development of profound neurologic signs in spite of aggressive antivenin therapy when treated with human- or veterinary-approved products, or even when treated with both.

In Madey’s opinion, there should be an antivenin developed specifically to include the most prevalent rattlesnake in our area, the canebrake. At present, there is no antidote to rattlesnake venom that is completely effective. So educate yourself on how to avoid these snakes, and have a plan in case a bite occurs.

Dr. Henri Bianucci and Dr. Perry Jameson are with Veterinary Specialty Care LLC. Send questions to petdocs@postandcourier.com.