Snake and Insect Bites

Snake and Insect Bites: Excerpt from The 5-Minute Pediatric Consult

Jill C. Posner, MD, MSCE

Snake and Insect Bites - BASICS

Snake and Insect Bites - description

• Injury to the human skin and/or subcutaneous tissues caused by bite, envenomation, or sting, causing usually local, but in some cases systemic effects
• Snake bites:
  • Crotalinae (pit vipers: Cotton mouths, copperheads, and rattlesnakes)
  • Elapidae (coral snakes)
• Spider bites:
  • Black widow (Latrodectus mactans)
  • Brown recluse (Loxosceles reclusa)
• Insect stings: Hymenoptera: Fire ants (Solenopsis), yellow jackets, wasps, bees

Snake and Insect Bites - epidemiology

• Only 15% of all snake bites are from poisonous snakes, and only ~2/3 of those involve true envenomation. 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 mainly in southern and midwestern states.
• 1–4% of the US population is at risk for anaphylaxis from Hymenoptera stings.

Snake and Insect Bites - incidence

• Annually, about 8,000 people sustain a poisonous snake bite in the US, and 12–15 fatalities occur.
• The incidences of black widow and brown recluse spider bites are unknown, mainly due to the inability to identify the species of spider involved in the majority of cases.
• 50–150 people die each year from sting anaphylaxis.

Snake and Insect Bites - pathophysiology

• Snake bites:
  • Although there are ~120 snake species in the US, only 15% envenomate substances are capable of causing fatal reactions.
  • Snake venom consists of numerous enzymes and polypeptides that are neurotoxic, cytotoxic, and hemotoxic.
  • Pit viper venom produces significant local inflammation, injury to the 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 20,000 species of predominantly venomous spiders in the US lack fangs capable of penetrating human skin or toxin strong enough to produce more than a mild reaction. The black widow and brown recluse spiders can cause significant harm, however.
  • The black widow venom, α-atrotoxin, 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 and sweating.
  • The brown recluse venom, mainly sphingomyelinase D, acts on RBC membranes, platelets, endothelial cells, and other cells, resulting in tissue infarction and necrosis. It causes the destruction of tissues at the site of the envenomation and triggers coagulopathy. Systemic symptoms are more likely to occur in children, presumably due to a smaller ratio of body weight to venom volume. Hemolysis, hemoglobinuria, disseminated intravascular coagulation, shock, seizures, and death rarely 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 wheal-and-flare reaction at the bite site.
  • The venoms of the bee, hornet, yellow jacket, and wasp contain antigens that trigger an IgE antibody response, resulting in allergic reactions that vary in severity from mild local effects to profound anaphylactic reactions.

Snake and Insect Bites - DIAGNOSIS

Snake and Insect Bites - signs & symptoms

Snake and Insect Bites - history

• 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, slitlike pupils, and a single row of subcaudal plates, and may have a rattle.
    • The corals have oval heads, 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. The brown recluse is small (1–1.5 cm), gray or reddish/brown, with a brown fiddle-shaped mark on the dorsum of the cephalothorax.
• Insect bites:
  • Type of insect
  • Previous history of insect bite allergy

Snake and Insect Bites - physical exam

• Crotalinae (pit viper) bites:
  • Intense local pain and 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 in the mouth.
  • Local ecchymosis and vesicles appear within the 1st few hours, and by 24 hours hemorrhagic blebs are present. Lymphadenitis may result.
  • Without treatment, necrosis extending throughout the bitten extremity generally ensues.
  • 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, 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
  • 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
  • 1–8 hours after bite, generalized pain and muscle rigidity, cramping abdominal pain
  • Children often have nausea and vomiting.
  • Respiratory difficulty may occur.
  • Hypertension, tachycardia, and cholinergic effects (diaphoresis, salivation, lacrimation, and bronchorrhea)
• Brown recluse spider bites:
  • Spectrum from minor local reaction to severe necrosis
  • Local reaction: Pain, erythema, swelling, and pruritus
  • 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 purple discoloration (necrosis) or blanching (vasospasm). Shortly after, a firm, purple necrotic lesion appears, and within 7–14 days black eschar is visible. Ulcer healing can take weeks to months.
• Insect bites:
  • Small local reactions: Painful, pruritic, urticarial lesion at the sting site
  • Large local reaction: Swelling and erythema, may become several centimeters in diameter
  • Anaphylaxis is rare with fire ants but occurs more frequently with bee stings.

Snake and Insect Bites - tests

Snake and Insect Bites - lab

• Snake bites: CBC, platelet count, PT/PTT, fibrinogen, fibrin split products, serum electrolytes, creatine kinase, creatinine, urinalysis
• Spider bites: CBC, serum electrolytes, creatinine, creatine kinase, urinalysis
• Insect bites: No tests done routinely

Snake and Insect Bites - differencial 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

Snake and Insect Bites - TREATMENT

• Crotalinae (pit vipers) bites:
  • Remove constrictive items (jewelry or clothing) and immobilize extremity at or below level of heart. Cryotherapy, arterial tourniquets, excision, and incision are not recommended. Oral suctioning is never recommended!
  • 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 the patient’s extremity.
• Elapidae (coral snakes): Constriction bands, suction, and drainage do not prevent coral snake venom absorption.

Snake and Insect Bites - general measures

• 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.
  • 2 Crotalinae antivenom products are available: Antivenin (Crotalidae) Polyvalent (ACP) (Wyeth Laboratories) and Crotalidae Polyvalent Immune Fab (Ovine) (Altana, Inc.), approved by the FDA in October 2000. 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.
  • Administration of ACP antivenom commonly is associated with the development of serum sickness and may be complicated by anaphylaxis. Skin testing prior to administration is recommended. Concurrent use of beta-blockers may be a relative contraindication to the administration of antivenom, as these drugs will decrease the effect of treatments for anaphylaxis.
  • Early data suggest that the use of Fab preparations is safe and effective and is associated with fewer immediate and delayed hypersensitivity reactions than ACP.
  • Supportive care: Volume replacement, packed red blood cells, platelets, fresh-frozen plasma, cryoprecipitate as indicated for hypovolemia and bleeding diathesis. Observe closely for respiratory and renal failure.
  • Frequent assessment of tissue perfusion; 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 is available from Wyeth Laboratories to treat envenomation by Micrurus (Eastern and Texas coral snakes), but no antivenom is available for the Micruroides (Arizona coral snake).
  • Local wound care, supportive care, analgesia, and tetanus vaccination as above
• Black widow spider bites:
  • To alleviate muscle pain and cramping, parenteral opioids and benzodiazepines can be administered.
  • 10% calcium gluconate has been used anecdotally, but is not of proven benefit.
  • Latrodectus-specific antivenom is available for more severe envenomations. Specific indications include young age, pregnancy, life-threatening hypertension and tachycardia, 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 all that is needed.
• Brown recluse spider bites:
  • Most bites can be treated on an outpatient basis with local wound care and symptomatic treatment for pain and pruritus.
  • Patients with systemic symptoms, serious infection, or extensive necrosis warrant hospitalization for aggressive supportive care.
  • Large necrotic areas may require surgical excision and skin grafting. Early surgical excision is contraindicated, as it may lead to further necrosis. The area of necrosis may not be fully demarcated until 4–8 weeks after the bite.
  • 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 local wound care and symptomatic treatment (antihistamine) for pruritus
  • If stinger remains in skin, remove by pinching or scraping. Emphasis should be on quick removal to decrease exposure to venom.
  • Life-threatening anaphylaxis should be treated with subcutaneous epinephrine (0.01 mL/kg 1:1,000, max 0.3 mL), methylprednisolone (2 mg/kg), and/or diphenhydramine (1.25 mg/kg).
  • Bacterial superinfection is rare, but if present can usually be treated with oral and/or topical antibiotics.

Snake and Insect Bites - FOLLOW UP

Snake and Insect Bites - prognosis

• Snake bites: Because the majority of snake bites are from nonvenomous snakes, and ~1/3 of bites from venomous snakes do not involve envenomation, the majority of bites cause only local injury.
• Spider bites: Children have severe reactions and rare fatalities.
• Insect bites: Most bites and stings cause minimal local effects, although some cause series systemic reactions and, rarely, death.

Snake and Insect Bites - bibliography

1. Clark RF, Selden BS, Furbee B. The incidence of wound infection following Crotalid envenomation. J Emerg Med. 1993;11:583–586.
2. Clark RF, Wethern-Kestner S, Vance MV, et al. Clinical presentation and treatment of black widow spider envenomation: A review of 163 cases. Ann Emerg Med. 1992;21:782–787.
3. Dart RC, McNally J. Efficacy, safety, and use of snake antivenoms in the United States. Ann Emerg Med. 2001;37:181–188.
4. Offerman SR, Bush SP, Moynihan JA, et al. Crotaline Fab antivenom for the treatment of children with rattlesnake envenomation. Pediatrics. 2002;110:968–971.

Snake and Insect Bites - CODES

Snake and Insect Bites - icd9

• 133.8 Chiggers
• 989.5 Bites of venomous snakes, lizards, and spiders

Book Source Details

• Book Title: The 5-Minute Pediatric Consult
• Author(s): M. William Schwartz MD; et al.
• Year of Publication: 2008
• Copyright Details: The 5-Minute Pediatric Consult, Copyright © 2008 Lippincott Williams & Wilkins.

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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.

More About This Book: Title: The 5-Minute Pediatric Consult Authors: M. William Schwartz MD; et al. Publisher: Lippincott Williams & Wilkins Copyright: 2008 ISBN: 0-7817-7577-9

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