Envenomation is the process by which venom is injected through a bite or sting by a venomous animal. Snake bites are the first thing many people think of when discussing venomous animals. However, lizards, various marine animals, and arthropods such as spiders, scorpions, and hymenopterans can produce venom injuries.
Despite the CDC identifying envenomation as a public health concern, limited training is provided to handle and treat these injuries properly. Improving physician’s ability to identify and manage a variety of envenomations can enhance the level of care provided to these patients.
Related: Envenomation in the US: Snakes, Lizards, Marine Life and Arthropods
Differentiating venom, poison, and toxungen
Poisonous and venomous are often used simultaneously but identify two separate scenarios when describing an animal.
- Venom. This is an endogenous substance produced by the animal that is actively injected via a sting or bite into a victim.
- Poison. These toxins can accumulate from exogenous or endogenous sources and passively be introduced into the body by inhaling, swallowing, or transdermal absorption.
- Toxungen. These substances are exogenously or endogenously produced but are transmitted actively through spraying, smearing, or spitting the substance onto the victim.
Clinical presentation and pathophysiology of snake bites
According to the CDC, approximately 7,000 to 8,000 venomous snakebites occur per year in the United States, resulting in five to ten deaths a year. In the US, approximately 98% of snakebites are inflicted by crotalids, or pit vipers.
The crotalids include three species of snakes common to the US: rattlesnakes, copperheads, and water moccasins (also called cottonmouth). This group makes up 98% of snake envenomations, with the remaining bites caused by coral snakes and non-native snakes legally or illegally maintained in zoos or private collections.
Crotalid venom contains several compounds with various actions including inflammatory, hemolytic, cytotoxic, and myotoxic effects. The severity of envenomation depends on several snake and victim factors. The size, age, health, last meal, last venom release, and species of snake can affect the severity of clinical presentation. Consider the age, health, and location of the bite as well.
Characteristics of crotalid envenomations:
- Dynamic reaction. Initially appears benign and progresses in severity over a couple of hours.
- Local tissue damage. Pain, edema, ecchymosis, and erythema are commonly seen with progression of leading edge.
- Systemic manifestations. Tachycardia, vomiting, distal site bleeding (epistaxis, gingival bleeding), neurotoxicity (cranial nerve palsies, respiratory muscle paralysis), hypotension, and cardiovascular failure.
Management of crotalid envenomations
- Airway, breathing, circulation (ABCs) require initial evaluation and periodically as needed.
- Initial evaluation of bite, marking leading edge and updating every 15 minutes.
- Judicial use of fluids to prevent excessive third-spacing.
- Pain control with opioids (fentanyl and hydromophone preferred agents).
- Laboratory studies, including PT, fibrinogen, serum electrolytes, blood urea nitrogen (BUN), creatinine, and complete blood count (CBC).
- Antivenom is indicated for progressing local damage, worsening hemotologic symptoms, and symptoms associated with systemic manifestations.
Coral snake envenomation differences
Unlike crotalid bites, coral snakebites do not produce significant local reactions with minimal swelling, erythema, or eccyhmosis. The venom of coral snakes is a neurotoxin that can take up to 12 hours to begin showing clinical features.
Commonly noted symptoms include pain, paresthesias, emesis, weakness, respiratory depression, and paralysis. Reserve antivenom for those displaying objective signs of respiratory or skeletal muscle weakness.
Clinical presentation and pathophysiology of lizard bites
The Gila monster (Heloderma suspectum) is the only venomous lizard in the US. The jaws of the Gila monster are extremely strong, which allows the lizard to maintain contact after the bite. To disengage the lizard, simply place the lizard on the floor, use two sticks to pry the mouth open, or try alcohol or water in the lizard’s mouth.
The complex mixture of toxins within the Gila monster produces a spectrum of symptoms. Toxins within the venom act to increase bradykinin release while also potentiating bradykinin receptors. Additionally, various phospolipases, hyaluronidase, and proteases produce local tissue damage and pain.
Clinically patients will present with significant swelling, pain, erythema, and lympadenitis around the bite area. Systemic symptoms will result in the development of angioedema, hypotension, tachycardia, nausea, vomiting, and prolonged diarrhea. Clinicians may also observe renal failure, coagulopathies, and electrolyte abnormalities after Gila monster envenomation.
Management of Gila monster envenomation
- Local wound care. Irrigate and debride devitalized tissue and remove any foreign bodies within the wound. Update tetanus immunization if needed.
- Pain control. Manage with intravenous opioids or ketamine.
- Aggressive airway management. Angioedema is a significant finding and can lead to airway compromise.
- Intravenous fluid resuscitation. Fluids should be used first but vasopressors may be needed.
- Therapeutic agents. Using bradykinin antagonists (icatibant), kallikrein antagonists (ecallantide), mast cell chymase, FFP, C1 inhibitor concentrate, corticosteroids, and antihistamines can manage angioedema.
Clinical presentation and pathophysiology of widow spider bites
Every state in the US has at least one native widow spider species, with 5 species seen across the US. Of the widow spiders, the female spider contains the venom and is responsible for envenomation.
The main active component of widow spider venom is α-latrotoxin, which causes a massive release of acetylcholine and catecholamines. This leads to pain, swelling, and erythema around the bite area. Characteristically, widow bites produce sustained muscle spasms affecting the ipsilateral muscles of the affected side of the body.
Patients will experience tachycardia, hypertension, nausea, vomiting, myocardial ischemia, priapism, rhabdomyolysis, and latrodectus facies. This is a constellation of facial muscle spasm, blepharospasm, eyelid edema, lacrimation, and risus sardonicus (forced grimace).
Management of widow spider envenomation
- Supportive care. Opioid analgesics, benzodiazepines for muscle spasms, and airway management as needed.
- Hypertensive therapy. Benzodiazepines and opioids help to manage but may need nicardipine and esmolol to manage refractory hypertension.
- Antivenom. Refractory pain and muscle spasms, patients at high-risk of complications from uncontrolled hypertension, and pregnant patients are appropriate candidates for antivenom.
Clinical presentation and pathophysiology of recluse spider bites
Recluse spiders are common in the Midwest and South. The spider bites those who inadvertently brush up against it. Recluse spider venom contains many compounds responsible for local tissue damage including hyaluronidase, collagenase, esterase, and various nucleases and proteases. Sphingomyelinase-D contained within the venom contributes to hemolysis and local tissue reactions.
Patients will develop a combination of diffuse erythematous rash, fever, myalgias, nausea, vomiting, abdominal pain, and diarrhea, often referred to as loxoscelism, 24–96 hours after the bite. Severe hemolysis can develop resulting in complications such as renal failure, pulmonary edema, DIC, and cardiac collapse.
Management of recluse spider envenomation
- Local wound care. Keep clean and treat wound expectantly. Few bites require plastic surgery to cover the wounds.
- Supportive care. Supportive care can help manage systemic symptoms.Use blood transfusions, plasmapheresis, and corticosteroids as needed.
Envenomations and proper management
The proper management of envenomation is key to the best possible outcome. Initiation of supportive care and use of antivenom are important aspects for treating venomous bites. Avoiding the use of tourniquets, ice therapy, incisions to remove venom, and attempting to catch offending animal are important in preventing additional damage and delays in treatment.
