Snake bites: Don’t let these cases rattle you!

Most veterinarians would agree that veterinary medicine has a seasonality to it. Each season comes with its own stereotypical set of cases. Spring is a time when the dermatologists reign supreme. I personally have induced vomiting more around Halloween than any other holiday. Winter has traditionally been a quieter time, perfect for us to pursue continuing education. Summer means you will be busy seeing quite a bit of everything. While (thankfully) not an everyday problem, pets presenting with snake bites tend to be a distinct summer phenomenon.

Commonality, species & location

Snakes are unarguably vital to the health of our ecosystems. They maintain balance in the food web and are critical for controlling pest populations. However, it is generally estimated that 150,000 dogs and cats are bitten by venomous snakes yearly in the United States, and bites from nonvenomous snakes are likely more common.

According to the Georgia Department of Natural Resources wildlife division, of the estimated 46 different species of snakes calling my state home, only six of those are venomous – the Cottonmouth, Copperhead, Timber Rattlesnake, Eastern Coral Snake, Eastern Diamondback Rattlesnake, and the Pigmy Rattlesnake. Texas has the honor of hosting the most snake species, with 68 species represented. Arizona has the distinction of having more rattlesnake species than any other U.S. state. Alaska has zero. So, it follows that venomous snake bites will only be a problem in some regions of the U.S., which is why many of us may be unfamiliar with current best practices when treating these cases.

Non-venomous snake bites

Most non-venomous snake bites will present as non-emergent, mild to moderately painful areas with localized swelling and bruising, usually with two small punctures at the site.

These can be treated easily as puncture wounds requiring localized wound care (thoroughly flushing and cleaning of the area), analgesics, anti-inflammatories (NSAIDs are acceptable in nonvenomous snakebites), and cage rest. Antibiotics are generally only indicated in cases of infection and are not recommended in any prophylactic capacity. Culture and sensitivity testing may be of benefit, depending on the wound’s state when you see it.

Venomous snake bites

Venomous snake bite treatment is typically emergent. These dogs present at your hospital in serious pain with mild to severe diffuse tissue swelling and bruising accompanied by their understandably frantic owners.

Treatment is determined by the severity of the bite using a mild/moderate/severe scale. Ideally, every patient presenting with a venomous snake bite should be admitted to the hospital or ER for monitoring and treatment. It is strongly recommended that these patients receive an IV catheter with LRS and an opioid pain medication (with preference given to those options that are fully reversible). A minimum database should be obtained for all blood pressure measurements, CBC with PT/PTT coagulation times, and renal values. Serial BP, PCV, and urine color/output should also be assessed in all cases. Immediate antivenom administration should be considered in all but the occasional very mild, stable patient. A mild case would be characterized by a systemically stable patient with minimal, non-progressive swelling based on an assessment within 2 hours of the bite. Depending on the bite’s location, the patient’s size, or other patient predisposing increased risk factors (think English Bulldog with a bite to muzzle), antivenom could still be warranted.

More on treatment

Three veterinary antivenom products are available to us in North America: Venom Vet, Rattler, and BI’s AVP. These three products are developed and explicitly licensed for animal use on all North American pit viper bites – rattlesnakes, copperheads, and cottonmouths. (Coral Snake antivenom is actually a human product that we use and differs from pit viper antivenom.) Studies on veterinary antivenom products have shown them all to have roughly the same efficacy but varying rates of allergic reactions. Rattler and AVP are whole antibody products with a larger molecule and a longer half-life. Since they stay in circulation longer, you may need to use less total antivenom when treating your patient. However, because they have the more reactive Fc portion of the antibody intact, they have a higher risk of hypersensitivity reactions (reported around 7.2-9.3%). The Venom Vet product is an F(ab)2 molecule with the more reactive Fc portion of the antibody removed. Repeated administration may be more necessary when using this product, especially in cases involving rattlesnakes or cottonmouths. Copperhead bites are often less severe and generally respond well to a single vial treatment and 24-hour hospital stay. Venom Vet has a reported hypersensitivity rate of 2.5-3.5%.

As these products have become more widely available, veterinary snake bite experts recommend that we stop defining our treatment success rate in cases of pit viper envenomation solely on patient survival rates, and I absolutely agree. The tissue damage and pain our patients experience can be extensive and intense; these secondary effects can result in owners electing euthanasia even after survival of the initial strike. Snake venom stays active in the body, causing ongoing systemic hemotoxic damage for up to 72 hours. Antivenom administration is the only treatment that can effectively counteract the venom and reduce/treat the tissue damage and pain. Treatment with Benadryl and steroids is of no benefit in cases of pit viper envenomation. The swelling is caused by the massive amount of tissue damage mediated through the hemotoxins, cytotoxins, and myotoxins in the venom itself. Histamines are not released during snake envenomation, and antihistamines administered to address the swelling are useless. Corticosteroids also do not address the swelling, redness, bruising, or pain caused as it does not counteract those toxins. NSAID therapy is contraindicated in the immediate treatment of these bites as these drugs can increase bleeding tendencies and perpetuate the risk of renal injury, both of which are already increased due to the venom.

Allergic reactions

They are treatable if allergic reactions occur, whether it is hives or anaphylaxis. Since your patient is already being monitored in the hospital with IV access available, you can readily administer Benadryl or epinephrine (given IM to reduce the chance of cardiac arrhythmias) as indicated. Signs of anaphylaxis include sudden hypotension (despite IV fluid therapy), urticaria, vomiting, and/or diarrhea. The antivenom should be discontinued until the allergic reaction has been controlled. If the patient needs more antivenom after a reaction, an epinephrine CRI can be given alongside the antivenom infusion in severe cases.

Following initial treatment

Once the patient is out of the emergent treatment period and stable, ongoing wound and pain management should be administered on an outpatient basis according to clinician preference and as patient needs are present. Clients should be prepared for the ongoing care their pets may require. It is not uncommon for extensive wounds to require weeks to months of regular care and bandage changes with the potential necessity of surgical reconstruction. Clients should be advised to monitor for increased swelling, bleeding, redness, necrosis of the skin, infection, or any rashes/fever/or vomiting that may indicate serum sickness. Pain medications, including gabapentin and opioids, should be provided based on patient pain levels. Antibiotics are not indicated prophylactically, only where evidence of active infection is present or in the cases of severe tissue sloughing and necrosis. In extreme cases of envenomation, it is also a good idea to recheck bloodwork 48 hours after discharge.

In closing

A recent study published by Emory University suggests that venomous snakebites are rising, especially in the Southern United States. (2) As veterinarians, our clients have high expectations. They are increasingly willing to provide their furry family members with the best care available. Not offering antivenom to our patients or reserving its use to only life-threatening cases, even when owners ask for it as a treatment, is no longer appropriate. With multiple veterinary-approved products readily available, it is time for us to routinely offer the very highest standard of care to our patients. I know that our clients and our patients will appreciate it.

References

Adesola Odunayo. Snake Envenomation. Clinical Skills/Emergency Medicine & Critical Care. 2019 April
https://www.cliniciansbrief.com/article/snake-envenomation

Eric J Lavonas, Charles J Gerardo, Gerald O’Malley, Thomas C Arnold, Sean P Bush, William Banner Jr, Mark Steffens, William P Kerns 2nd.  Initial experience with Crotalidae polyvalent immune Fab (ovine) antivenom in the treatment of copperhead snakebite. 2004 Feb;43(2):200-6.  doi:10.1016/j.annemergmed.2003.08.009.

Peterson ME, Matz M, Seibold K, Plunkett S, Johnson S, Fitzgerald K. A randomized multicenter trial of Crotalidae polyvalent immune F(ab) antivenom for the treatment of rattlesnake envenomation in dogs. J Vet Emerg Crit Care (San Antonio). 2011;21(4):335-345

Bush SP, Ruha AM, Seifert SA, et al. Comparison of F(ab’)2 versus Fab antivenom for pit viper envenomation: a prospective, blinded, multicenter, randomized clinical trial. Clin Toxicol (Phila). 2015;53(1):37-45. doi: 10.3109/15563650.2014.974263

Armentano RA, Schaer M. Overview and controversies in the medical management of pit viper envenomation in the dog. J Vet Emerg Crit Care (San Antonio). 2011;21(5):461-470. doi: 10.1111/j.1476-4431.2011.00677.

Mariah Landry, Rohan D’Souza, Shannon Moss, Howard H. Chang, Stefanie Ebelt, Lawrence Wilson, Noah Scovronick. The Association Between Ambient Temperature and Snakebite in Georgia, USA: A Case-Crossover Study.  11 July 2023, https://doi.org/10.1029/2022GH000781
Cory Woliver, National Veterinary Snakebite Support Article, 3 August 2022