We all love to bask in the California sun and rattlesnakes are no exception. Snakebite envenomation is something that is frequently seen in the ER, in fact, we treated three pets for this just this past weekend alone! Sadie, an 11-week old Cocker Spaniel, was one of those patients. She was gardening with her Mom when a rattlesnake bit her.
Poisonous snakes of the United States belong to two groups: pit vipers and elapids. Pit vipers are the largest group and include at least 26 subspecies of rattlesnakes (Crotalus spp.), with the Western Rattlesnake being the most common in our region. Click this link for an excellent resource guide that includes pictures of the many species of California rattlesnakes.
How does the venom work?
An understanding of the function of venom is helpful in appreciating how envenomation works. The snake uses its venom to immobilize the victim and predigest body tissues. There are over 50 types of enzymes in pit viper venom, with a minimum of 10 in any individual snakes venom. Additionally, there are many other non-enzymes present in the venom, called killing fractions, which are 50 times more toxic than the “crude” venom. When the venom destroys the body tissues, it is possible for up to 1/3 of a pet’s body fluid to be lost into the tissue spaces within several hours, which can result in life-threatening drops in blood pressure resulting in shock.
What makes a bad bite worse?
Several factors influence the severity of snakebites. The most important factors are the volume of venom injected and the toxicity of the venom itself. Other factors include:
- The amount of regenerated venom since the last bite: there is more venom and it is more concentrate if the snake hasn’t bitten in a while.
- The age of the snake: younger snakes have more “potent” venom.
- Aggressiveness of the snake: the more threatened they feel, the more concentrated the venom.
- Motivation of the snake: offensive strikes are more severe.
- The size of the pet being bitten: smaller dogs and cats are more severely affected than large dogs due to their small body size to venom ratio (less body to “absorb” the amount of venom).
- The size of the bite.
- The location of the bite: the “best” place to be bitten is in the legs or face as the regional swelling and changes in the local blood supply can actually slow the uptake of the venom; envenomation to the body is more concerning as the broader area allows for the venom to be absorbed more rapidly; bites to the tongue are the worst and result in rapid and devastating clinical signs.
- The time elapsed from bite until seeking medical treatment.
- The amount of physical activity since the time of the bite.
What are the general signs of a snakebite wound?
Snakebites are not always easy to diagnose, especially if it was an unobserved bite and if a pet has a heavy hair coat that may hide puncture wounds. With pit viper bites, you can usually see bleeding puncture wounds and single or multiple puncture sites may be observed. The initial signs are marked swelling, which is due to the tissue destruction and body fluid “leaking” into the damaged area (see the picture of the little Chihuahua, showing a what a typical bite to the face looks like). Clinical signs may develop immediately or be delayed for several hours. Bruising and skin discoloration often occurs within hours of the bite because the venom causes the blood to not clot. There is usually intense and immediate pain at the site of the bite, which helps differentiate snakebites from other causes of swelling, and swelling is generally progressive for up to 36 hours. You can also see collapse, vomiting, muscle tremors, and depression in breathing.
What to do if a snake bites your pet:
- If your pet is bitten by a snake, it is best to assume it is a venomous bite.
- Seek veterinary attention as soon as possible!
- If the swelling is not in the face, muzzle your pet (if you can do it safely) to avoid being bitten: snake bites are very painful and your pet may unintentionally snap at you; if the swelling is in the face, avoid touching this area all together.
- Immobilize the part of your pet that has been bitten by the snake, if this can be done safely; try to keep the area at or below the level of the heart.
- Keep your pet calm and immobile, carry if necessary.
What NOT to do (and the mumbo jumbo myths)
- Do not try to suck out the venom! (This technique only works for John Wayne in old Western movies).
- Do not attempt to “make an X” and cut open the area around the bite (you will only cause a wound).
- Do not bother to use a Snake Bite Kit or Extractor Pump (they will actually do more harm to your pet- and your wallet!).
- Do not apply ice to the area: this constricts the blood vessels locally and actually concentrates the venom causing severe muscle damage to the area.
- Do not rub any substances into the bite: the venom has entered the blood stream, and any substance applied topically is ineffectual.
- Do not apply a tourniquet: you will only succeed in causing further tissue damage and possibly create a need for limb amputation.
- Do not allow your pet to move about freely.
- Do not attempt to capture the snake for later identification (you’d be surprised…)
Tips for prevention:
- Stay on open paths while hiking with your pet.
- Keep your pets on leash away from high grass and rocky outcrops where snakes like to rest.
- Don’t let your pet explore holes or dig under rocks.
- Keep an open ear for that telltale rattling noise and keep your pet at your side until you determine where the sound is coming from, and then move slowly away.
- If you see a snake that sees you, remember that a snake can strike only a distance of half its body length; give the snake time to “just go away” as they are not looking to interact with you or your pet.
- Don’t let your pet examine a dead snake as they still can envenomate.
- For around your home: cut off the snakes food supply and shelter by mowing close to the house, storing firewood away from the house, plugging up holes in the ground, and limiting birdseed waste which can attract rodents to your home.
What is the treatment?
Since the onset of clinical signs can be delayed for several hours, all pets that have been bitten by a snake should be hospitalized for at least 12 hours and ideally 24 hours. Although most pets generally need to be supported and monitored, the vast majority (95%) do survive with early and proper treatment.
Antivenom is the only proven treatment against pit viper envenomation, and the earlier it is administered, the more effective its action. The biggest downside to antivenom is cost, and it can range anywhere from $450-$700 per vial. Usually a single vial will control the envenomation but several vials may be necessary, especially in small dogs or cats. Many animals may do “fine” without it, but it does decrease the severity of clinical signs, as well as speed overall recovery with a reduction in complications. Blood work is also recommended to monitor your pet’s platelet count as well as clotting times of the blood. IV fluid support, intensive pain management, antibiotics and wound monitoring are required for best clinical outcomes. Blood and plasma transfusions are sometimes needed in severe envenomation.
What about the vaccine?
There is a “snake-bite vaccine” that may be useful, but there have been no controlled studies for its effectiveness. The main benefit of the vaccine is that it may create protective antibodies to neutralize some of the injected venom, and in turn may lessen the severity of the clinical signs. One of the biggest myths is that if your pet has had the vaccine, then they don’t need to be treated if they are bitten; this is not true, and they still require the same treatment despite being given a vaccine or not!
Thankfully, most snakes will try to avoid you and your pets and typically only bite as a last resort. But if your pet does happen to get bitten by a snake that you think might be venomous, it is best to err on the side of caution and get medical attention immediately. As always, feel free to ask questions or leave comments!