Basics
Description
- Injury to the human skin and/or subcutaneous tissues caused by bite, envenomation, or sting, causing local but sometimes systemic effects
- Snake bites
- Crotalinae (pit vipers: cottonmouths, copperheads, and rattlesnakes)
- Elapidae (coral snakes)
- Spider bites
- Black widow (Latrodectus mactans)
- Brown recluse (Loxosceles reclusa)
- Insect stings: Hymenoptera, fire ants (Solenopsis), wasps (including hornets and yellow jackets), bees
Epidemiology
- Only 15% of all snake bites are from poisonous snakes, and only ¢ ¼2/3 of those involve true envenomation. Crotaline snakes are the most common cause of venomous snake bites in the United States. Almost 3,500 Crotaline exposures were reported to U.S. poison control centers in 2010. Coral snake bites constitute <1% of all snake bites.
- The black widow spider is found in most areas of North America but especially in southern New England. The brown recluse spider is found in southern and midwestern states.
- 1 " 4% of the U.S. population is at risk for anaphylaxis from Hymenoptera stings.
Incidence
- Annually, ¢ ¼8,000 people sustain a poisonous snake bite in the United States, 99% of which are from crotaline snakes, and 5 " 6 fatalities occur.
- The incidences of black widow and brown recluse spider bites are unknown.
- 50 " 150 people die each year from sting anaphylaxis.
Pathophysiology
- Snake bites
- Snake venom consists of numerous enzymes and polypeptides that are neurotoxic, cytotoxic, and/or hemotoxic.
- Pit viper venom produces significant local inflammation and injury to vascular endothelium and may lead to coagulopathy, thrombocytopenia, and shock.
- The venom of the coral snake is primarily neurotoxic and may produce neuromuscular paralysis and respiratory depression.
- Spider bites
- Most of the 20,000 species of predominantly venomous spiders in the United States lack fangs capable of penetrating human skin or toxin strong enough to produce more than a mild reaction. However, the black widow and brown recluse spiders can cause significant harm.
- The black widow venom,α-latrotoxin, is a neurotoxin that stimulates myoneural junctions and nerve terminals by increasing synaptic release of acetylcholine and by initiating a massive influx of calcium, causing severe skeletal muscle pain and cramping and autonomic disturbances such as hypertension, tachycardia, and diaphoresis. Pediatric patients are more severely inflicted given the ratio of milligram of venom to kilogram of body weight.
- The brown recluse venom, mainly sphingomyelinase D and hyaluronidase, acts on erythrocyte membranes, platelets, endothelial cells, and other cells, resulting in tissue infarction and necrosis. Systemic symptoms are more likely to occur in children, presumably because of a smaller ratio of body weight to venom volume. Hemolysis, hemoglobinuria, renal failure, DIC, shock, seizures, and death may occur.
- Insect stings
- The fire ant bites with its jaws and then swings its head around to inflict multiple stings. The venom has a direct toxic effect on mast cell membranes, causing an immediate urticarial reaction at the bite site.
- The venoms of the bee and wasp (hornet and yellow jacket) contain antigens that trigger an IgE antibody response, resulting in allergic reactions that vary in severity from mild local effects to anaphylaxis.
- Cross reaction between Hymenoptera species occurs. Those who react to fire ants may also react to bees and wasps.
Diagnosis
History
Alert
- If the snake is brought in for identification, use caution! The head of a dead snake can deliver a venomous bite for up to 1 hour after death/decapitation.
- Snake bites
- Poisonous snakes have triangular-shaped heads, a pit (heat sensor in front of each eye), fangs, slit-like pupils, and a single row of subcaudal plates and may have a rattle:
- The corals have oval heads and round pupils yet are still poisonous.
- Nonpoisonous snakes have oval heads, no pits, rows of small teeth, round pupils, a double row of subcaudal plates, and no rattles.
- In the Elapidae family, the coral snake can be differentiated from the benign king snake by the pattern of the colored bands: "Red on yellow, kill a fellow; red on black, venom lack. "
- Spider bites: identification of spider (rare): The black widow is about the size of a quarter, glossy black, gray, or brown, with a red, orange, or yellow hourglass-shaped marking on the ventral surface. A single bite can deliver a lethal dose of venom. The brown recluse is small (1 " 1.5 cm), gray, or reddish/brown, with a violin-shaped mark on the dorsum of the cephalothorax.
- Insect bites
- Identify type of insect (bee, wasp, ant).
- Assess for history of insect bite allergy.
Physical Exam
- Crotalinae (pit viper) bites
- Intense local pain/burning occur in the 1st few minutes, followed by edema and perioral numbness that may extend to the scalp and periphery. Paresthesias may be accompanied by a metallic taste.
- Local ecchymosis and vesicles appear within the 1st few hours, and by 24 hours, hemorrhagic blebs are present.
- Without treatment, edema and tissue necrosis through the bitten extremity may occur. Compartment syndrome is rare.
- Nausea, vomiting, weakness, chills, and sweating can also occur with systemic absorption of venom.
- Neuromuscular involvement (e.g., diplopia, dysphagia, lethargy) can develop within several hours.
- Signs of hypovolemic shock, hemorrhagic diathesis, coagulopathy, and neuromuscular dysfunction may occur in life-threatening envenomations.
- Elapidae (coral snake) bites
- Mild, often unimpressive local signs and symptoms (pain, swelling) but significant neurologic effects that include extremity paresthesias, weakness, fasciculations, and bulbar dysfunction that can progress to flaccid paralysis and respiratory failure
- Inspect bite wound for fang punctures.
- Carefully assess neurovascular integrity, and consider compartment pressures if severe edema.
- Black widow spider bites
- No local symptoms associated with bite
- Within 8 hours after bite, regional or generalized pain and muscle cramping, fasciculations; abdominal rigidity without tenderness is a hallmark sign.
- Children often have nausea and vomiting.
- Respiratory difficulty may occur.
- Hypertension, tachycardia, and cholinergic effects (diaphoresis, salivation, lacrimation, and bronchorrhea)
- Death may occur from respiratory or cardiovascular collapse.
- Syndrome can last 3 " 6 days.
- Brown recluse spider bites
- Spectrum from minor local reaction to severe necrosis
- Local reaction: pain, erythema, swelling, and pruritus; classic "bull 's eye " lesion or "red-white-and-blue " sign
- Ischemia and skin necrosis: A bright red papule appears within a few hours of the bite and can evolve within 48 " 72 hours into a hemorrhagic vesicle surrounded by blue discoloration (necrosis) or white blanching (vasospasm), the bull 's eye. Shortly after, a firm, purple necrotic lesion appears, and within 7 " 14 days, black eschar is visible. Ulcer healing can take weeks to months, leaving a deep scar.
- Insect bites
- Small local reactions: painful, pruritic, urticarial lesion at the sting site
- Large local reaction: edema and erythema, may be several centimeters in diameter
- Anaphylaxis is rare with fire ants but occurs more frequently with bee stings.
Diagnostic Tests & Interpretation
Lab
- Snake bites: CBC, platelet count, PT/PTT, fibrinogen, fibrin split products, electrolytes, creatine kinase, creatinine, urinalysis
- Spider bites: CBC, PT/PTT, fibrinogen, electrolytes, creatinine, creatine kinase, urinalysis, Coombs test
- Insect bites: no tests done routinely
Differential Diagnosis
- Black widow spider bites: acute abdomen, renal colic, opioid withdrawal, tetanus
- Poisonous snake bites: nonpoisonous snake bite (leaves scratches, not punctures), rodent bites, thorn wounds
- Brown recluse spider bite: other spider bites, insect bites and stings (including Lyme), cellulitis, poison ivy/oak, Stevens-Johnson syndrome, toxic epidermal necrolysis, erythema nodosum, chronic herpes simplex, purpura fulminans, diabetic ulcer, gonococcal hemorrhagic lesion, pyoderma
Treatment
- Crotalinae (pit vipers) bites
- Remove constrictive items (jewelry or clothing) and immobilize extremity at or below level of heart. Cryotherapy, arterial tourniquets, ice immersion, incision, excision, and oral suctioning are not recommended!
- Focus on rapid transport to medical facility.
- Address airway, breathing, and circulation.
- The use of a constrictive band is controversial. Main indication is for cases of prolonged transport time to a medical facility or rapid progression of systemic symptoms. A flat band is placed 5 " 10 cm proximal to the bite, with enough pressure to impede lymphatic and superficial venous flow but not arterial flow. 1 " 2 fingers should fit easily between the band and patient 's extremity. Be careful of progressive edema leading to tightening of constrictive band if applied. Also remember that these bands can worsen local cytotoxic effects.
- Another option is a compression bandage alone with immobilization of the involved extremity (pressure-immobilization method). This is thought to delay systemic absorption of venom.
- Elapidae (coral snakes)
- Constriction band, suction, and drainage do not prevent coral snake venom absorption.
Additional Treatment
General Measures
Consider contacting your local poison control center to assist with diagnosis and management. The national phone number for all centers is 1-800-222-1222.
- Crotalinae (pit vipers) bites
- Wound care: irrigation and dressing
- Determine if envenomation has occurred via serial examinations (q30min) and laboratory studies (q4h).
- Antivenom: Administration of antivenom should be made in consultation with a toxicologist and/or herpetologist. General indications include progressive local swelling, pain or ecchymosis, and any systemic signs or symptoms.
- Crotalidae Polyvalent Immune Fab (CroFab) is the Crotalinae antivenom product approved by the FDA. Antivenin (Crotalidae) Polyvalent (ACP) was often associated with serum sickness and anaphylaxis and is no longer manufactured.
- Data suggest that the use of CroFab is safe and effective and is associated with fewer immediate and delayed hypersensitivity reactions than ACP, although they do occur and must be monitored.
- Some hospitals (in endemic areas) and many zoos stock antivenoms. In addition, the regional poison control center may have access to the Antivenom Index and will be able to help locate the nearest supply.
- Early administration of Fab within 6 hours is advised. Initial dose is 4 " 6 vials of Fab diluted in 250 mL normal saline infused over 1 hour. Dosing is based on amount of venom injected, not weight of patient.
- Supportive care: volume replacement, packed red blood cells, platelets, fresh frozen plasma, cryoprecipitate as indicated for hypovolemia and bleeding diathesis. Observe for respiratory and renal failure.
- Frequent assessment of tissue perfusion and measurement of compartment pressure; fasciotomy only for elevated compartment pressures
- Empiric antibiotics are controversial but may be indicated in cases of extensive tissue involvement.
- Analgesia and tetanus prophylaxis
- Elapidae (coral snakes)
- Crotalinae antivenom is ineffective in treating Elapidae envenomation. Antivenom formerly manufactured by Wyeth Laboratories is no longer in production. Currently, there are only 2 lots of FDA-approved Elapidae antivenom in the United States, both of which have expired on October 2014. It is not known at this time when more will be manufactured.
- Any degree of neurotoxicity or systemic symptoms is an indication for antivenom therapy. Prophylactic therapy should be avoided due to limited supply and need to preserve antivenom.
- Local wound care, supportive care, analgesia, and tetanus vaccination
- Black widow spider bites
- To alleviate muscle pain and cramping, parenteral opioids and benzodiazepines can be administered.
- Calcium infusions had been used anecdotally but have not proven to be effective.
- Latrodectus-specific antivenom is available for more severe envenomations given via IV infusion. Specific indications include young age, pregnancy, life-threatening hypertension and tachycardia, respiratory difficulties, or severe symptoms refractory to other treatment measures. Administration of an equine serum preparation has been associated with hypersensitivity reactions and occasionally death. 1 vial is generally sufficient.
- Brown recluse spider bites
- Most bites can be treated on an outpatient basis with local wound care with Burow solution or hydrogen peroxide and symptom treatment for pain and pruritus.
- No antivenom is available in the United States.
- Patients with systemic symptoms, serious infection, or extensive necrosis warrant hospitalization, IV fluids, and aggressive supportive care.
- Skin grafting or debridement may be warranted for wound management. Surgical excision is no longer indicated.
- Neither dapsone nor hyperbaric oxygen therapy has proved to be effective; dapsone in children is associated with methemoglobinemia.
- Insect bites or stings
- Rarely require more than ice and antihistamine for pruritus
- If stinger remains in skin, remove by pinching with forceps or scraping. Emphasis should be on quick removal to decrease exposure to venom. Do not squeeze venom gland.
- Life-threatening anaphylaxis should be treated with subcutaneous epinephrine (0.01 mL/kg 1:1,000 or 1 mg/mL, max 0.3 mL), methylprednisolone IV/IM (2 mg/kg), and/or diphenhydramine IV/IM (1.25 mg/kg).
- Bacterial superinfection is rare but, if present, can usually be treated with oral and/or topical antibiotics.
Ongoing Care
Prognosis
- Snake bites: Because the majority of snake bites are from nonvenomous snakes, and ¢ ¼1/3 of bites from venomous snakes do not involve envenomation, the majority of bites cause only local injury. However, once serious injury is established, prognosis becomes unclear.
- Spider bites: Children have severe reactions and rare fatalities.
- Insect bites: Most bites and stings cause minimal local effects, although some cause serious systemic reactions and, rarely, death. For those patients with severe anaphylactic reactions, discharge the patient with a subcutaneous epinephrine autoinjector.
Additional Reading
- Anz AW, Schweppe M, Halvorson J, et al. Management of venomous snakebite injury to the extremities. J Am Acad Orthop Surg. 2010;18(12):749 " 759. [View Abstract]
- Goto CS, Feng SY. Crotalidae polyvalent immune Fab for the treatment of pediatric crotaline envenomation. Pediatr Emerg Care. 2009;25(4):273 " 282. [View Abstract]
- Quan D. North American poisonous bites and stings. Crit Care Clin. 2012;28(4):633 " 659. [View Abstract]
- Schmidt JM. Antivenom therapy for snakebites in children: is there evidence? Curr Opin Pediatr. 2005;17(2):234 " 238. [View Abstract]
- Walker JP, Morrison R, Stewart R, et al. Venomous bites and stings. Curr Probl Surg. 2013;50(1):9 " 44. [View Abstract]
- Warrell DA. Venomous bites, stings, and poisoning. Infect Dis Clin North Am. 2012;26(2):207 " 223. [View Abstract]
Codes
ICD09
- 989.5 Toxic effect of venom
- 919.4 Insect bite, nonvenomous, of other, multiple, and unspecified sites, without mention of infection
ICD10
- T63.481A Toxic effect of venom of arthropod, accidental, init
- T63.001A Toxic effect of unsp snake venom, accidental, init
- T63.301A Toxic effect of unsp spider venom, accidental, init
- T63.331A Toxic effect of venom of brown recluse spider, acc, init
- T63.091A Toxic effect of venom of snake, accidental, init
- T63.021A Toxic effect of coral snake venom, accidental, init
- T63.011A Toxic effect of rattlesnake venom, accidental, init
- T63.311A Toxic effect of venom of black widow spider, acc, init
SNOMED
- 402150002 Insect bite reaction (disorder)
- 61288004 poisoning by venomous snake (disorder)
- 217665000 poisoning due to venomous spider (disorder)
- 40119006 poisoning due to brown recluse spider venom (disorder)
- 217666004 Poisoning due to black widow spider venom (finding)
- 217659000 poisoning due to rattlesnake venom (disorder)
- 217661009 poisoning due to viper venom (disorder)
- 217653004 poisoning due to coral snake venom (disorder)