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Knowing the threat and treatment options for snake toxins

Heather Smith Thomas Published on 24 August 2012
Treating a horse for a snake bite

The rattlesnake is the most common poisonous snake in the U.S. and part of a larger family called pit vipers – which include the water moccasin, copperhead and cottonmouth. All of these can be dangerous to livestock.

The danger and potency of a bite depends on the amount of venom injected by the snake and the types of toxins in the venom.

A large snake that hasn’t eaten for several days, with a full pouch of venom, is more deadly than a small snake or any snake that has recently bitten and killed prey.

Venom contains several types of toxin and the primary toxin may depend on the type of snake, according to Dr. Ginger Elliot, a veterinarian in Guthrie, Texas, who has seen a number of snakebites in large animals during her 30 years of ranch practice.

“Of the 21 species of rattlesnakes found in the western U.S., the Prairie Rattlesnake is the most numerous and the Western Diamondback is the largest. The rare Mojave Rattlesnake inhabits southern parts of California, Nevada, Arizona, New Mexico and southwestern Texas,” she says.

The toxins in rattlesnake venom immobilize and kill prey (generally small rodents) and break down their body tissues to start the digestive process.

“The main toxins are mycotoxins (the primary toxins in Western Diamondback venom), which create rapid swelling, pain and bleeding at the bite site and hemotoxins (the main toxin found in Prairie Rattler venom) that damage the blood vessels.

The toxins create inflammation, tissue destruction and blood vessel leakage – allowing the venom to spread,” explains Elliot.

Dr. A. Jacques Fuselier, from the Rural Animal Health Management System, College of Veterinary Medicine at the University of Illinois, spent time in Louisiana and had a lot of experience with livestock bitten by water moccasins as well as rattlesnakes.

“Most bites are on the lower limb or muzzle, especially if cattle encounter the snake at a stock pond,” he says.

A cow with a swollen face from snakebite

Cattle may be curious and get bitten on the face or muzzle – or on the leg if they walk past the snake on their way to water.

“On hot days they may try to get belly-deep in water to cool off and may get bitten on the dewlap or muzzle.

These bites are the ones I’m most concerned about because the rapid swelling can make it difficult for them to breathe,” he says.

The poison’s effectiveness is in direct relationship to the size of the animal. A large animal will generally survive the bite unless systemic infection develops or the bite is on the muzzle.

In that situation, swelling from the bite may restrict air passages and can result in suffocation. The type of toxin can also be a factor.

Venom from the Mojave Rattler, for instance, contains more neurotoxins, which may be more likely to kill a large animal. In most cases, however, the damage is generally local because the poison isn’t strong enough to get very far.

“As a veterinarian I don’t see very many snakebitten cattle because most of them are treated by the owner, or in some situations the owner finds the animal several days later and it’s doing OK,” says Elliot.

Treatment

There are two things to worry about in a snakebitten animal, according to Robert Cope, a veterinarian in Salmon, Idaho: swelling and infection.

Swelling on the face can shut off the airways, and dying tissue around a bite can send infection through the body, causing fever and blood poisoning (septicemia).

A bite in soft tissues can become infected, says Cope. Cleaning and disinfecting the bite can help. He also advises antibiotics until danger of infection is past. Your veterinarian can prescribe the appropriate antibiotic.

DMSO (dimethyl sulfoxide) will also reduce the pain, swelling and inflammation, says Cope. DMSO gel or liquid can be rubbed over the area that’s swelling.

If the animal was bitten on the face and is having trouble breathing, liquid DMSO can also be given orally, mixing it with a little warm water and squirting it into the back of the mouth with a syringe, where it is rapidly absorbed and can help keep the air passages open by halting the tissue swelling.

In severe cases of swelling on the head, where the animal is in danger of suffocation, immediate treatment is crucial.

“If you can catch it early enough, when it is just starting to swell, the veterinarian can put an endotracheal tube with a cuff into the nasal passage to keep it open while we do something to reduce the swelling,” says Fuselier.

“If the veterinarian can’t get there quickly, the stockman could stick a 6-inch to 8-inch piece of hose (or plastic syringe barrel) into one of the nostrils,” he says. For a calf, smaller tubing would work. Lubricating the end of the tube makes it easier to insert.

If the swelling is too far along and the airways are already squeezed shut (the animal can’t breathe), an emergency tracheostomy is necessary to maintain an active air passage.

This is best done by a veterinarian, but if there is no way the veterinarian can get there in time, the stockman could try to do it.

“You make a vertical incision through the skin, along the windpipe, right in the middle of the throat – so you can get down to the rings of the trachea.

Then use your fingers to open that slit a bit wider side-to-side so you can make a stab incision between the rings. If that’s not enough of a hole, you can cut a small circle, removing a portion of the cartilage ring to make a bigger hole.

“Often, a pocketknife stab is enough between the rings to get it open for airflow. If you have to, you can slip a small piece of hose or tube into that hole to keep it open,” says Fuselier. After the swelling is resolved and the windpipe is no longer restricted, the incision can be sutured.

“A bite on the leg is usually not quite as serious, depending on where it is. The higher on the leg (such as near the armpit or groin), the worse it might be. The toxins could then get into the bloodstream quicker,” he says.

“But usually what you see first is a localized swelling from the bite. It may then progress along the leg as a generalized swelling or cellulitis in the soft tissues.

The best way to treat that would be to surgically debride that area to cut out the dead tissue and get down to the healthy tissue and clean the wound,” he says.

Snake bites often become infected and this can be more dangerous than the bite itself, says Cope. There usually isn’t enough toxin to kill a large animal, but bacteria often enter with the bite – and the dying tissue makes an ideal place for bacteria to multiply.

“Every animal responds differently to the toxins,” says Fuselier.  end_mark

PHOTOS

TOP: A ranch hand prepares to inject anti-inflammatory medication to reduce swelling that’s shutting off this horse’s airways. Note the tube in each nostril, keeping the airways open.

BOTTOM: This calf was bitten under the jaw, resulting in massive swelling. Photos courtesy of Heather Smith Thomas.

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