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Snakebite!
Cultural prejudices, lack of knowledge vilify snakes; clients should understand basics when bites occur


DVM360 MAGAZINE


Many bites in horses are thought to be "dry" or non-venomous because the snake has to put a lot of biological work into making its poison and does not seek to waste it. Because the snake can sense the size of the horse, it bites only to get away. This may be another reason why equine deaths from snakebites are not common.

What to adviseClients should be aware of a few steps to take in the event of a snakebite.

Most snakes will give larger animals a few seconds to get out of the way so encourage clients to be calm and to slowly back their horses away from snakes. Try to confirm the bite and identify the snake if possible. Snakebites can be difficult to locate on the body because of hair, bleeding or swelling. By the time that most veterinarians see affected horses, the swelling will have become severe enough that the original bite punctures cannot be found. Horses that are bitten on the nose or muzzle can swell so much that their nostrils close and breathing can be difficult to impossible.

Encourage trail riders to carry two 6-inch pieces of garden hose. Advise these clients to pass the lubricated hose into the nostrils of a horse that is bitten in this area to keep airways open. These horses then can be transported and treated.

Increased heart rate causes higher blood pressure and the dissemination of snake venom to larger areas of the horse's body so every effort should be made to calm the horse, especially if the horse was exercising heavily prior to the bite.

Instruct clients to keep the horse in one spot and get a trailer to it if possible or to slowly walk the horse to the nearest road if the terrain does not allow trailer pick-up. Apply a wide tourniquet proximal to the bite to slow the toxin's spread. Wash the bite area with Betadine and water. The mouth of a snake contains many potentially harmful bacteria that will contaminate the wound. Do not cut the bite area. Recent research shows that this old practice can allow venom access to even more tissue and may actually contribute to further damage.

Research has also shown that application of cold or hot compresses will definitely worsen the damage. Clients may use the rubber suction cup in snakebite kits to try to remove some of the venom, but these cups are not very effective. Snakebites should never be suctioned by mouth!

Three focal areasOn presentation to a veterinarian, the diagnosis of a snakebite has usually been made and the treatment approach should focus on three main areas.

  1. First, prevent or delay absorption of venom. Many times there is a substantial time delay between the bite and its discovery or in the call for veterinary assistance. This is common in horses bitten while at pasture or in a stall for the evening. The next morning the owner typically finds a horse in pain with a severely swollen leg. Cleaning and voluminous flushing of the wound, if it can be located, may be all that can be done at this stage. It is thought that infiltrating the bite area with saline in an attempt to dilute the toxin will actually aid in its dispersal throughout the damaged vessels and lymphatics so this should be avoided.
  2. The second main treatment should be to neutralize any absorbed venom with appropriate antivenin. Many states have hot line numbers linked to a poison control center that will provide antivenin availability information in your area. Rural hospitals are your best bet for locating the antivenin necessary. Be sure to have epinephrine available because of the anaphylactic response possibility, since many antivenins are equine origin products.
  3. Fight the effects of the toxin and maintain cardiovascular function. Maintain severely affected horses with intravenous fluids. This volume replacement should be tempered with a desire to limit the spread of venom throughout the body. Corticosteroids are advised to counter shock and to help lessen tissue destruction. Broad-spectrum antibiotics should be given and, since many snakes' mouths contain Pseudomonas bacteria, gentamycin and penicillin are the drugs of choice. DMSO can be added to the intravenous fluids. Its action in stabilizing tissue can aid in some cases.

Skin and tissue damage may be the hardest aspects of snakebites to treat. Treatment designed to reduce swelling and to prevent toxin spread in the initial few hours many be the most important action that will help with later tissue repair. Compression bandages that limit edema are very helpful. Treatment with cold laser or monochromatic light in the later healing stages may benefit lymphatic drainage and repair and yield encouraging results.

Other predatorsWhile discussing snakebites it's important to remember plenty of other potentially serious types of bites are commonly seen in horses.

Gila monsters, found in certain areas of the United States, can cause tissue necrosis and painful bites. Scorpions are found throughout the south and southwest. Their bite can cause massive edema with serous leakage through the skin of the affected horse's leg. Laminitis or tendon breakdown in the contralateral limb is a potential complication in all such types of bites if damage is extensive enough.

Leg wraps, heel or frog pads and appropriate anti-inflammatory therapy is necessary in these cases. Brown recluse and black widow spiders account for many serious equine bites each year. The treatment approach is generally the same regardless of the causative agent of the bite.

Dr. Marcella, a 1983 graduate of Cornell University's veterinary college, was a professor of comparative medicine at the University of Virginia. His interests include muscle problems in sport horses, rehabilitation and other performance issues.


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