• Venoms are complex chemical mixtures designed either for defending or for hunting.
  • Various venom delivery systems exist.
  • Most systems consist of specially evolved exocrine gland mechanisms to make and store venom and a sophisticated delivery apparatus.
• Stings are delivered through a posterior structure (stinger) and are primarily defensive.
• Bites refer to injection through structures associated with the mouth that are primarily for handling prey.
• Envenomation is the injection of venom through a bite or sting.

• Incidence
  • In 2005 the American Association of Poison Control Centers National Poison Database reported 2,547,394 exposures.
  • 82,151 (3.2%) were a result of a bite or sting.
  • Of the 1460 total deaths recorded in the database, 7 (0.5%) were from bites and stings, and none involved children.
• Prevalence
  • Bites and envenomations ranked number 10 in all age groups in the National Poison Database but did not make the top 20 in children < 6 years.

Hymenoptera

• Prevalence
  • Systemic reactions occur in < 5% of patients.
  • Large local cutaneous reactions occur in 2.3–18.6% of the general population.
  • Biphasic anaphylactic reactions, characterized by the return of symptoms 6–10 hours after initial symptoms resolve, occur in up to 20% of patients.
  • Death by honeybee or wasp envenomation is rare, especially in children.
  • IgE-mediated type 1 anaphylaxis, although uncommon, is usually responsible for related deaths.
  • Massive envenomation involving hundreds of stings may also result in death.
  • Hymenoptera envenomation is the second-leading cause of anaphylactic reactions, after penicillin.
    • It accounts for more deaths in the US than any other envenomation.
• Fire ants
  • Fire ant envenomations are becoming an increasingly important concern in the US.
  • Systemic allergic reactions occur in ≤ 16% of patients treated for fire ant stings.
  • Serious reactions, including anaphylaxis, occur in ≤ 2%.
  • The literature suggests a 20–30% annual attack rate in areas where imported fire ants are endemic.
  • The highest sting rate (close to 50%) occurs in persons < 20 years.

Arachnids

• Approximately 50 spider species are of medical importance.
  • Most are venomous and can cause serious injury.
  • Fatalities from spider bites are rare.
• Scorpion envenomation may be life threatening in children.
  • Systemic manifestations tend to be more common in children < 10 years.

Snakes

• Envenomations by snakes in North America are overwhelmingly caused by indigenous Crotalinae, also called pit vipers.
  • ~20–25% of pit viper bites are dry, meaning they do not result in envenomation.
• Coral snakes constitute < 1% of envenomations.
• Nonindigenous snakes in zoos or kept as exotic pets are responsible for a small percentage of envenomations.
• All sea snakes are venomous; none inhabit the coastal waters of North America.
• Most bites in the US occur in the Southwest.
• Body area
  • Most bites are inflicted on the upper extremity, including fingers, hand, and arm.
  • Less commonly affected sites are the leg, foot, and torso.
• Mortality
  • The number of deaths from snakebite in the US ranges from 0 to 14 per year.
  • Most snakebite deaths are associated with absence of medical care, errors in medical management, or presence of an underlying medical condition.
  • Children are at increased risk for serious sequelae because of their lower body mass and relatively high venom dose compared with adults.

Hymenoptera

• In the US, Hymenoptera are responsible for most insect stings.
  • Family Apidae (honeybees)
  • Family Bombidae (bumblebees)
  • Superfamily Vespidae (paper wasps, white-faced hornets, yellow hornets, and yellow jackets)
  • Superfamily Formicidae (harvester ants and native and imported fire ants)
• All Hymenoptera possess a stinger located posteriorly.
• Reactions may be either a direct effect of the venom or an IgE–mediated allergic reaction.

Winged Hymenoptera

• The sting apparatus, or aculeus, of wasps (vespids) and honeybees resembles a stylet with 2 shafts that pulls the stinger deep into the flesh.
• Unlike the honeybee, the vespid sting stylet is less likely to remain in the victim.
• Honeybees die after stinging; because vespids can withdraw their stingers, they can sting multiple times.
• Venoms of the winged Hymenoptera contain many different protein components that account for the observed reactions.

Ants

• Fire ants bite the skin of their victims with their mandibles, then arch their bodies to inject venom through a lancet-shaped stinger located at the distal end of their abdomen.
  • If undisturbed, they will sting repeatedly in a circular pattern, using their mandibles as a pivot, injecting venom with each sting.
• Harvester ants also bite the skin with their mandibles and envenomate their victim through a sting.
  • Their venom contains a larger fraction of protein constituents than fire ant venom and is more similar to other Hymenoptera venoms.

Arachnids

• Class Arachnida includes 2 orders: Araneae (spiders) and Scorpionidae (scorpions).
• Envenomations can result in significant morbidity, but deaths are rare.

Spiders

• A diverse group with approximately 40,000 species worldwide
• In North America, spiders most commonly involved in human exposures are:
  • Loxosceles species (brown recluse spider, also known as the violin spider or fiddleback spider); 11 species in the US, usually the Southeast and Southwest
  • Latrodectus species (black widow spider)
  • Tarantulas

Scorpions

• Centruroides exilicauda, or the black scorpion, is the only medically relevant species of scorpion in the United States.
  • Found in Arizona and adjacent southwestern states
• Its venom is a potent neurotoxin that activates neuronal sodium channels and results in excessive firing of affected neurons, including both the adrenergic and parasympathetic systems.

Snakes

• Venomous snakes of North America can be divided into 2 families: Viperidae (subfamily Crotalinae) and Elapidae.
  • Crotalinae, also called pit vipers, includes rattlesnakes, water moccasins or cottonmouths, copperheads, pygmy rattlesnakes, and massasauga rattlesnakes.
  • Elapidae includes coral snakes, as well as nonindigenous cobras and mambas.

Crotaline snakes (pit vipers)

• Their highly mobile, retractable, hollow fangs function like a hypodermic needle.
  • Usually penetrate to subcutaneous tissue, whereas the fangs of larger snakes penetrate dermal or subcutaneous structures and deposit venom into the muscle
• Venom is generally absorbed through the lymphatic system.
• Crotaline venom is a complex mixture of biologically active proteins and peptides capable of damaging vascular endothelial cells.
  • This leads to increased permeability to plasma and erythrocytes into the extravascular space and ultimately can result in hypotension and shock.
  • Venom is spread throughout the body as a result of the action of hyaluronidase and its integrity-reducing effect on connective tissue.
• Pit viper venoms are designed to immobilize and digest prey; prominent effects include:
  • Direct tissue injury resulting from enzymatic degradation
  • Local inflammatory responses exaggerated by metalloproteinases
  • Increased intracellular calcium in skeletal muscle, resulting in prolonged contraction and necrosis
  • Increased permeability of erythrocyte membranes, changing their morphology and potentially causing hemolysis
  • Damage to mast cell membranes, causing histamine release
  • Isolated defibrination caused by coagulopathy following fibrinolysis and thrombin-like peptide actions
  • Thrombocytopenia resulting from platelet aggregation at sites of tissue injury and from a direct effect of venom on individual platelets, particularly from rattlesnake venom.
  • Neurotoxins are present in varying degrees, notably in the Mojave and timber rattlesnakes, and can produce weakness, paralysis, and myokymia.
• The notion that juvenile rattlesnakes are more dangerous than adult snakes is a misconception.

Coral snakes

• Coral snakes tend to be small, secretive, and mild-mannered unless provoked.
• Coral snakes lack facial pits, are diurnal, and have fixed fangs and nearly round pupils.
• Bites may produce superficial scratches or definite fang marks; retroverted teeth gnaw or chew on their prey, making coral snakes difficult to shake off.
• Local tissue injury is uncommon.
• Venom causes paresthesias and paralysis by inhibiting acetylcholine receptors at the neuronal synapse.

• An amount of venom that would not harm an adult may be disastrous for a child.

Hymenoptera

• The risk of a systemic reaction appears to be increased:
  • In patients with a history of multiple stings
  • In patients who are stung within a few weeks of a previous sting
• In patients with a history of anaphylaxis, the risk of anaphylaxis with subsequent stings is 35–60%.
• Atopic patients do not appear to be at greater risk of systemic complications, but the severity of their symptoms may be greater.
• History of a large local reaction does not reliably predict progression to systemic complications.
  • Risk of subsequent anaphylaxis after a large local reaction is approximately 5–10%.
• Children are at high risk because of their failure to perceive the risk and inability to escape.

Winged hymenoptera

• Yellow jacket wasps are common near exposed food and garbage.
• If disturbed, any wasp or bee will sting in self-defense.
• Eyes, mouth, and nostrils may be selectively targeted.

Fire ants

• Trespassing into their territory or disturbing a nest will incite aggressive, swarming behavior, often resulting in multiple stings.
• Ants do sometimes attack victims indoors, especially following heavy rains.

Arachnids

• Most spiders are not aggressive and only bite in self-defense when:
  • Humans invade their territory.
  • The spider becomes lost in such items as bedclothes.
• Tarantulas kept as pets pose a risk to the unsuspecting child.
• Loxosceles (brown recluse spider) bites are usually the result of accidental contact.
• Scorpion stings usually result from accidental contact with a scorpion trapped in linen or clothing or during outdoor play.

Snakes

• The typical snakebite victim is a young white adult male who is bitten while handling or playing with a snake.
• Alcohol consumption increases risk.
• Most bites are inflicted on an upper extremity, including fingers, hand, and arm.

Winged Hymenoptera

• Local
  • The nonallergic reaction is a direct result of envenomation through mast cell degranulation and the production of a wheal-and-flare response causing:
    • Erythema
    • Swelling
    • Pain
    • Itching
  • In conjunction with these reactions, some patients may experience:
    • Headache
    • Nausea
    • Malaise
  • Skin and soft-tissue necrosis in the weeks after a Hymenoptera sting have also been reported.
  • Corneal stings
    • May result in damage through toxic and immunologic reactions
    • Stingers retained in the eye may cause corneal edema with striate and toxic keratopathy.
    • Immunologic reactions can result in extensive inflammation, uveitis, and inflammatory glaucoma.
• Systemic
  • Common systemic manifestations include:
    • Urticaria
    • Angioedema
    • Wheezing
    • Shortness of breath
    • Stridor
    • Nausea
    • Vomiting
    • Diarrhea
    • Abdominal pain
    • Malaise
    • Dizziness
    • Anaphylaxis
    • Dysphagia
    • Dysarthria
    • Hoarseness
    • Weakness
    • Confusion
  • Effects on the hematologic system include:
    • Hemolysis with associated hemoglobinuria and hemoglobinemia
    • Thrombocytopenia
    • Disseminated intravascular coagulation
  • Multiple stings from Africanized bees may cause:
    • Hemolysis
    • Thrombocytopenia
    • Rhabdomyolysis (skeletal and myocardial)
    • Acute tubular necrosis
  • Systemic symptoms typically develop within 24 hours, although delayed onset (2–6 days) has been reported.

Fire ants

• Local
  • Stings tend to be multiple and cause immediate local burning and itching.
  • Soon after, the area becomes erythematous and raised.
  • This reaction usually subsides after 30–60 minutes.
  • The classic pathognomonic finding of small, sterile pustules developing 4–24 hours later is more common with stings of imported fire ants.
    • Pustules may occur in rings or lines consistent with fire ant stinging behavior.
    • Pustules usually resolve over 3–10 days.
  • Some patients develop a large local reaction similar to that of other Hymenoptera stings.
  • The initial wheal-and-flare reaction evolves into an erythematous, pruritic, warm, indurated area around the sting site.
  • Large local reactions may progress over 48 hours and may not subside for 7 days.
  • The pathophysiologic mechanism of large local reactions is not clear and may be confused with cellulitis.
• Systemic allergic reactions are similar to those associated with other insects and include:
  • Bronchospasm
  • Angioedema
  • Urticaria
  • Pruritus
  • Laryngeal edema
  • Hypotension
  • Anaphylaxis
  • Seizures
  • Mononeuritis
  • Guillain-Barré syndrome
  • Serum sickness
  • Nephritic syndrome
  • Worsening of preexisting cardiopulmonary disease
• Direct systemic toxic effects of fire ant venom are not well understood.
• No deaths have been attributed to date to fire ant venom.

Harvester ants

• Unlike imported fire ants, harvester ants do not leave characteristic skin lesions.
• Their sting resembles that of other insects and may be associated with allergic reactions.

Loxosceles (brown recluse spider)

• Local, cutaneous
  • The bite itself does not cause much discomfort and may go unnoticed.
  • A minor stinging or burning sensation may be felt at the site.
  • Erythema, pruritus, pain, and edema typically develop within 2–8 hours.
  • Symptoms may be followed in the next 24–48 hours by a blue-gray halo surrounding the erythematous center.
  • Vesicles or bullae containing serous or hemorrhagic fluid soon follow.
  • Local ischemia and necrosis result in formation of a black eschar within 7–10 days of the bite.
  • This necrotic area may expand slowly for weeks, especially in fatty areas that have delicate blood supplies such as the abdomen, buttocks, and thighs.
  • The eschar is shed after 2–5 weeks, and an ulcer remains that may take weeks to months to heal.
• Systemic manifestations of the bite are less common.
  • The most common symptoms are:
    • Fever
    • Chills
    • Malaise
  • Symptoms usually occur within 24 hours of the bite and also may include
    • Nausea
    • Vomiting
    • Diarrhea
    • Arthralgia
    • Urticaria or maculopapular rash
    • Hemolytic anemia
    • Disseminated intravascular coagulation
    • Jaundice
    • Renal failure
    • Transverse myelitis
    • Seizures
    • Shock

Latrodectus (black widow spider)

• Local
  • A bite may go unnoticed or may be experienced as a pinprick or burning sensation.
  • 2 small puncture lesions may be visible.
  • Within 30 minutes, pain develops at the site and in the regional lymph nodes.
  • Central pallor at the bite site with surrounding erythema has been described.
  • Inflammatory response is mild.
  • An unusual reaction may include compartment syndrome, which may improve after antivenin administration.
• Systemic
  • The onset of systemic symptoms is frequently sudden, with crampy, skeletal muscle pains in the legs, abdomen, back, and chest and associated autonomic dysfunction.
  • The most frequent systemic signs and symptoms are:
    • Generalized abdominal pain or back pain
    • Local or extremity pain
    • Hypertension
    • Diaphoresis
    • Isolated abdominal or chest pains
    • Nausea
    • Vomiting
    • Tachycardia
    • Restlessness
    • Salivation
    • Bronchorrhea
    • Priapism
    • Urinary retention
    • Periorbital edema
    • Tremor
    • Convulsions
    • Muscle symptoms
    • Target-shaped skin lesions
    • Irritability
    • Agitation
  • Abdominal rigidity may mimic peritoneal irritation.
  • Respiratory paralysis, heart failure, and myocarditis have been reported.
  • Patients who do not receive antivenin may experience protracted symptoms that may last for several days to 1 week, including:
    • Fatigue
    • Weakness
    • Paresthesias
    • Generalized aches
    • Diaphoresis
    • Headache
    • Sleeplessness
    • Excessive sweating
    • Impotence
    • Mental status changes
    • Transient hemiparesis

Tarantulas

• Most bites are no more severe than a bee sting.
• Occasionally result in local erythema, swelling, and pain
• Nausea and vomiting may occur.
• Some genera (Lasiodora, Grammostola, Acanthoscurria, and Brachypelma) can release urticaria-producing hairs from their abdomen by rubbing their hind legs on the area.
  • Can result in local histamine release with mild pruritus
  • Itching can last for weeks.
  • Hairs may cause considerable itching and discomfort in eyes or airways.

Scorpions

• Not all stings result in clinical evidence of envenomation.
• Patients may have both adrenergic and cholinergic symptoms.
• Local
  • Pain at the sting site with or without paresthesias is common.
  • In mild envenomations, pain may be the only symptom and may account for such manifestations as unexplained crying in infants.
  • Local erythema and swelling may surround a small puncture wound, but the sting site is often unidentifiable.
  • Paresthesias and pruritus are frequent.
• Systemic
  • Manifestations can be dramatic and usually develop within 60 minutes of sting.
    • Tachycardia or bradycardia
    • Central nervous system dysfunction, a finding that is rare in adults
    • Severe hypertension in one-third to two-thirds of the victims
      • Can be associated with acute hypertensive encephalopathy
      • May not respond to medical management
    • Heart failure
    • Acute lung injury
    • Pulmonary edema
    • Neurologic toxicity includes excessive cholinergic stimulation resulting in salivation, sweating, and vomiting.
    • Profound sialorrhea
    • Skeletal muscle findings include twitching or jerking of the extremities, which may be severe enough to be mistaken for seizure activity.
    • Rhabdomyolysis
    • Nystagmus
    • Seizures and agitation

Crotaline snakes

• Local
  • Presence of ≥ 1 fang marks, typically with ragged edges that may be obscured as a result of trauma resulting from first-aid attempts
  • Pain in > 90% of envenomations
  • Edema
  • Ecchymosis
  • Erythema develops 15 minutes to 4 hours after the bite.
  • Hemorrhagic toxins in pit viper venom may cause blood to ooze from the puncture sites, and hemorrhagic bullae may develop.
  • Muscle necrosis
  • Lymphangitis and lymphadenopathy with tender regional lymph nodes and warmth in the injured body part as a result of lymphatic spread of venom
• Systemic
  • Malaise
  • Weakness
  • Lightheadedness
  • Diaphoresis
  • Visual disturbances
  • Nausea
  • Vomiting
  • Syncope
  • Myokymia
  • Perioral paresthesias
  • Metallic or minty taste
  • More severe systemic effects include:
    • Altered sensorium
    • Acute respiratory distress syndrome
    • Respiratory depression
    • Hemodynamic instability leading to circulatory collapse
    • Renal failure
  • A consumptive coagulopathy is frequently present in serious envenomations and is characterized by:
    • Hemolysis
    • Unmeasurable international normalized ratio (INR) and activated partial thromboplastin time
    • Hypofibrinogenemia
    • The presence of fibrin degradation products
    • Thrombocytopenia (< 20,000 cells/mm)
    • Generalized hemorrhage
  • When combined with defibrination, venom-induced thrombocytopenia may appear as disseminated intravascular coagulation.
  • Mojave rattlesnake venom may cause more neurotoxicity, specifically myokymia, than the venom of other rattlesnakes.

Coral snakes

• Local
  • Erythema and local pain are transient or absent.
  • Most patients have evident fang marks.
• Systemic
  • May be delayed for 12 hours
  • May appear suddenly
  • May include bulbar paralysis with:
    • Ptosis
    • Dysphagia
    • Dysarthria
    • Excessive salivation
    • Paresthesias
    • Euphoria or apprehension
    • Drowsiness
    • Dizziness
    • Weakness
    • Confusion
    • Nausea
    • Vomiting
    • Diaphoresis
    • Muscle tenderness or fasciculations
    • Tremors
    • Altered sensorium
    • Drowsiness
    • Ophthalmoplegias that cause visual disturbances
  • These manifestations may be followed by:
    • Seizures
    • Respiratory paralysis
    • Pulmonary hemorrhage
  • It can be unclear which findings are the result of the venom itself and which are the result of hypoxia.

Hymenoptera

Flying Hymenoptera

• Differential diagnosis of the local reaction includes:
  • Other arthropod envenomations
  • Puncture wounds with reactive erythema or cellulitis
  • Simple cellulitis
• Differential diagnosis of systemic reactions include:
  • Any other cause of allergic reaction
  • Reactive airway disease
  • Infectious processes
• Other causes of stridor, wheezing, and allergic reaction should be considered if a sting site cannot be identified.
• A stinger may sometimes be found at the sting site, which usually indicates a honeybee sting or, in some cases, a yellow jacket sting.
• Most patients cannot reliably identify the insect that stung them.

Fire ants

• Large local reactions must be carefully examined to differentiate them from cellulitis.
• Absence of lymphadenopathy and lymphangitis supports the diagnosis of large localized reaction.

Arachnids

• Differential diagnosis includes:
  • Other arthropod bites
  • Skin infections
  • Injury caused by chemical and physical agents

Loxosceles (brown recluse spider)

• In the absence of a definitive history of spider bites, other diagnostic possibilities must be considered, such as:
  • Emboli
  • Thrombi
  • Focal vasculitis
  • Envenomation by other insects or reptiles
  • Fat herniation with infarction
  • Pressure sore
  • Pyoderma gangrenosum
  • Poison oak or ivy
  • Cutaneous manifestation of gonorrhea or herpes simplex
  • Diabetic ulcer
  • Purpura fulminans
  • Erythema nodosum
  • Erythema multiforme
  • Stevens-Johnson syndrome
  • Abusive or self-inflicted trauma
• Cutaneous anthrax has been misdiagnosed as Loxosceles envenomation.
• Other species of spiders have been implicated in the cause of necrotic skin lesions similar to Loxosceles.
  • Argiope (orb weaver spider)
  • Chiracanthium (sac spider)
  • Lycosa (wolf spider)
  • Phidippus (jumping spider)
  • Tegenaria agrestis (hobo spider)
• The temptation to diagnose all necrotizing skin lesions as Loxosceles bites should be avoided.
• Positive identification of the spider is important not only for correct diagnosis but also to understand true clinical course of Loxosceles envenomation.

Latrodectus (black widow spider)

• Causes of acute abdominal pain should be part of the differential diagnosis.
• Close resemblance of the autonomic hyperactivity seen after black widow spider bites and those seen in organophosphate poisoning

Scorpions

• 2 factors make establishing the correct diagnosis difficult.
  • The sting site may not be identifiable
  • The child may not be able to communicate the history of a sting clearly.
• Some of the differential diagnostic possibilities are:
  • Seizure disorder
  • Intraabdominal process
  • Phenothiazine or cholinergic poisoning
  • Allergic reaction
• Asthma has been misdiagnosed in some children with wheezing and respiratory distress.
• Progression of symptoms is not predictable.
  • Progression to serious symptoms usually occurs in < 5 hours, if at all.
  • Numbness, tingling, and pain may persist for 2 weeks.
  • Duration of symptoms has been found to be inversely related to the age of the patient.

Snakes

• The helpfulness of identifying the type of snake is controversial.
• The bite reflex in recently killed or decapitated snakes can remain intact, rendering them capable of biting even when they are dead.
• If medically necessary, a herpetologist from a zoo or aquarium may be able to help with positive identification.

Hymenoptera

• No specific laboratory test is useful in the acute management of Hymenoptera stings.

Arachnids

• Loxosceles (brown recluse spider)
  • No current clinical laboratory study can confirm the presence of arachnid venom–related necrosis.
  • Several research tests, including enzyme-linked immunosorbent assay and passive hemagglutination inhibition test, have been studied but are not in clinical use.
  • Complete blood count, coagulation profile, electrolytes, and renal function should be monitored in systemic illness.

• Latrodectus (black widow spider)
  • No specific laboratory test helps establish a diagnosis.
  • Leukocytosis and hyperglycemia are common.
  • Creatine phosphokinase may be increased as a result of increased muscle activity.
  • Serum calcium levels are normal.

• Scorpions
  • No confirmatory laboratory test exists.
  • Leukocytosis, cerebrospinal fluid pleocytosis, and increased creatine phosphokinase have been reported.

Snakes

• Crotaline snakes (pit vipers)
  • Only of minor assistance to asses severity
  • May be useful in determining whether envenomation has occurred
  • Tests include:
    • Complete blood count with differential
    • Erythrocyte morphology (to assess for spherocytosis)
    • INR and prothrombin time
    • Plasma thromboplastin time
    • Fibrinogen level
    • Fibrin-split products
    • Platelet count
  • If these studies reveal any abnormalities, or if the patient has clinical symptoms, then envenomation must be assumed and the clinician should perform:
    • Analysis of electrolytes
    • Blood urea nitrogen
    • Blood type and cross-match
    • Urinalysis
• Coral snakes
  • Do not mandate routine laboratory screening
  • If respiratory insufficiency is suspected, obtain:
    • Transcutaneous pulse oximetry
    • Arterial blood gases

• Rarely indicated, except in the case of a scorpion sting, where echocardiography can reveal hypodynamic ventricular motion with decreased systolic performance

• Rarely indicated, except in the case of a scorpion sting, where electrocardiographic changes are common and include:

• Ischemic electrocardiographic pattern
• Nonspecific ST-T changes or ST elevation or depression consistent with myocardial infarction

• The primary care clinician must be aware of local venomous species and be able to recognize and treat the injuries caused by them.

• In North America, venomous species include:
  • Arthropods
    • Bees
    • Wasps
    • Hornets
    • Ants
  • Arachnids
    • Spiders
    • Scorpions
  • Snakes
    • Pit vipers
    • Coral snakes

Winged Hymenoptera

• Stinger removal
  • Traditional teaching advocates stinger removal by scraping with a hard-edged object, such as a credit card, to prevent pressure on the venom sac.
  • However, experimental data show that removal of the stinger with the fingers does not increase envenomation.
  • Rapid removal of the stinger by any means is most effective in minimizing envenomation.
  • Removal of bee stingers embedded for > 1 minute will not reduce envenomation; most venom empties from detached honeybee stings within 10–20 seconds.
• Nonallergic local reactions
  • Nonallergic local reactions require symptomatic treatment, including:
    • Cool compresses (ice should not be placed directly on the skin)
    • Elevation
    • Local wound care
  • No further evaluation is necessary.
  • If local itching is bothersome
    • An oral histamine-1 (H₁) antagonist, such as diphenhydramine, may help.
  • Local allergic reactions require similar care as nonallergic reactions.
  • For very large cutaneous reactions
    • Prednisone (0.5–2 mg/kg/day given in 1–4 doses for 3–5 days) may be useful.
• Acute management of corneal bee sting includes:
  • Preventing secondary infection with broad-spectrum topical antibiotics
  • Reducing inflammation with topical corticosteroids
  • Treating anterior uveitis
  • Early detection and treatment of inflammatory glaucoma
  • Providing pain relief
  • Surgical removal of the embedded stinger is controversial.
  • Pulse corticosteroids may prevent permanent loss of vision.
• Medications
  • Mild systemic allergic reactions
    • Diphenhydramine or another H₁-antihistamine
    • Supportive care
    • Observation
  • Severe systemic allergic reactions
    • Epinephrine
      • 0.01-mL/kg dose of 1:1000 aqueous epinephrine solution is injected subcutaneously.
      • The original dose should not exceed 0.3 mL, but may be repeated in 15 minutes.
      • Susceptible individuals should carry epinephrine self-administered kits when they go outdoors.
      • After kit is used, medical help should be sought because the effect of the drug is short lasting.
    • H1-antagonists
    • Corticosteroids
    • Intensive supportive care
  • Severe systemic reactions from direct toxic effects of massive envenomation require:
    • Intensive supportive care
    • Therapy similar to that for anaphylactic reactions
    • Careful monitoring for:
      • Rhabdomyolysis
      • Thrombocytopenia
      • Cardiac arrhythmias
      • Renal failure
      • Possible dialysis

Fire ants

• Mild local reactions are treated conservatively with
  • Cool compresses
  • Oral antihistamines
  • Wound care
• Large local reactions may require oral antihistamines and systemic corticosteroids.
• Systemic allergic reactions are treated similarly to those from any cause.
• Epinephrine is the mainstay of therapy, coupled with:
  • H1-antagonists
  • Systemic corticosteroids
  • Vigorous supportive care as appropriate

Harvester ants

• Treatment is the same as that for other Hymenoptera stings.

Loxosceles (brown recluse spider)

• Management is controversial.
• Serial observation, wound cleansing, cool compresses, splinting of the affected extremity, and tetanus prophylaxis are often-suggested measures.
• Symptomatic relief with antipruritics and analgesics may be useful in some cases.
• Different therapies have been proposed, including:
  • Systemic corticosteroids
  • Antibiotics
  • Antihistamines
  • Colchicine
  • Dapsone
  • Electric shock
  • Hyperbaric oxygen
  • Metronidazole
  • Surgical excision
  • Skin graft
• Delay surgical repair of skin defects until necrotic demarcation is discrete and no further spread occurs, which takes about 8 weeks.

Latrodectus (black widow spider)

• Most black widow spider bites require only:
  • Cool compresses
  • Elevation of the affected extremity
  • Tetanus update (if needed)
  • Analgesics
• In more severe cases, suggested treatments include:
  • Oxygen
  • Cardiac monitoring
  • Intravenous access
• Muscle cramps may be relieved with opiates and muscle relaxants.
  • The following have been used, with varying results:
    • Diazepam
    • Methocarbamol
    • Calcium gluconate (the efficacy of 10% calcium gluconate has been questioned)
• Patients who do not receive antivenin will gradually improve over the next 12–48 hours.
  • Some patients may experience protracted symptoms.
• Latrodectus antivenin of equine origin neutralizes venom from all related species.
  • Patients should be tested for horse serum hypersensitivity before administration to prevent death from anaphylaxis.
  • Consider in cases of:
    • Severe envenomation with evidence of respiratory distress, marked hypertension, and cardiovascular compromise
    • Pregnancy
    • Protracted symptoms that do not respond to analgesics and muscle relaxants
  • Response is usually dramatic after antivenin infusion.
  • Administration of antivenin may decrease length of hospital stay and prevent lingering neurologic complications.

Tarantulas

• Local wound care and a tetanus update are all that is needed in most cases.
• Antihistamines and oral analgesics may be helpful.
• Adhesive tape or irrigation with saline solution may be used to remove the urticaria-producing hairs from the skin.

Scorpions

• There is no standard therapy.
• Treatment is primarily supportive, with the use of cold compresses and analgesics.
• Severe cases require aggressive supportive therapy.
• Antihypertensives have been used, including:
  • Calcium-channel blockers
  • Hydralazine
  • Prazosin
  • Captopril
• Afterload reducers are front-line therapeutic agents for hypertension, including:
  • Angiotensin-converting enzyme inhibitors
  • Calcium-channel blockers
  • Prazosin
• Concern about reflex tachycardia has led some clinicians to favor prazosin and captopril.
• The use of diuretics for pulmonary edema is controversial.
• Atropine may be used with caution if cholinergic symptoms become severe.
  • Atropine may improve hypersecretion, obviating the need for more aggressive therapy.
• Treatment should be guided by thorough hemodynamic monitoring.
• Benzodiazepines are generally administered for seizures and agitation.
• Corticosteroid therapy has been shown to be of no benefit.
• Currently, no scorpion antivenin is approved by the US Food and Drug Administration.
• Clinical trials are ongoing of an equine-derived antigen-binding fragment (Fab₂) antivenin.

Snakes

• First aid
  • Observe the approximate size and characteristics of the snake only if this can be done without danger of remaining within striking range.
  • Move the patient as little as possible.
  • Mark the victim’s skin with a pen to indicate the area of swelling and the time and repeat every 15 minutes.
  • Remove rings, watches, and constrictive clothing.
  • Immobilize the affected limb by splinting as if for a fracture, keeping the limb below the level of the heart.
  • Regardless of early symptoms, transport the victim to the nearest medical facility at a safe speed.
  • Avoid use of:
    • Ice (tissue damage)
    • Aspirin (anticoagulation)
    • Alcohol or sedative drugs (vasodilation)
    • Stimulants, such as caffeine (acceleration of venom absorption)
  • As soon as possible, start basic life support, including volume expansion and Trendelenburg position for patients with hypotension.
  • Patients should be kept as calm as possible during transport because agitation hastens venom distribution.
• Controversial forms of first aid
  • Incision and suction should not be performed.
  • Constricting bands that impede blood or lymph flow should not be used.
  • Loose-fitting bands placed in an effort to reduce lymphatic flow have been advocated but have not been shown to be of clear benefit.
  • Although the routine use of an extractor device for field care is not advocated, patients with an extractor or suction device in place should not remove it until they arrive at a health care facility.
• In-hospital care
  • Medical history of known envenomations should include
    • Size and species of the snake
    • Circumstances of the bite (eg, through clothing, alcohol related)
    • Number of bites and body area affected
    • First-aid methods used
    • Time of bite and transport time
    • Previous snakebite history
    • Allergy to horse- or sheep-derived products (eg, drugs, food, animal products)
    • Tetanus immunization status
  • Coexisting medical conditions, with special attention paid to the cardiovascular, pulmonary, and neurologic systems, should be factored into clinical management.
  • Snakebites from exotic (nonindigenous) species, which usually occur in zoo employees or in those illegally keeping the snake as a house pet, should be part of the history-gathering process.
  • Clinical presentation and medical management of an exotic bite may differ from bites of North American poisonous snakes.
• Local therapy
  • Local wound care includes:
    • Gentle irrigation
    • Nonconstrictive immobilization
    • Elevation of the bitten extremity
    • Close observation
  • Circumferential measurements at several points along the affected limb should be performed at baseline and regularly repeated.
  • Intercompartmental pressures should only be measured when the patient’s symptoms are consistent with compartment syndrome.
  • In cases of suspected compartment syndrome, clinical diagnosis requires objective evidence of increases in compartment pressure to > 30 mm Hg.
  • Fasciotomy has not been shown to be beneficial; it may lengthen hospitalization and cause significant long-term morbidity.
  • Digital dermotomy may be indicated on clinical grounds.
• Use of antivenin
  • Crotaline polyvalent immune Fab (ovine) antivenin (CroFab)
    • CroFab has replaced the horse serum–based antivenin ACP as the drug of choice.
    • CroFab is a purified ovine polyvalent Fab immunoglobulin fragment product produced by immunizing sheep with venoms of 4 crotaline snakes.
    • Indicated in treatment of patients with minimal or moderate North American crotaline envenomation
    • Administer within 6 hours.
    • Delayed use of CroFab has been reported with successful correction of significant toxicity incurred after crotaline envenomation.
  • Antivenom use should proceed simultaneously with supportive therapy.
• Steps in using antivenin
  • Prepare to manage anaphylaxis.
    • Anaphylactic reaction to CroFab is uncommon but has been reported.
    • All patients receiving antivenin should be monitored, and 2 sites for intravenous access should be considered—1 for the antivenin and 1 for emergency drugs and fluids.
    • Intravenous epinephrine, diphenhydramine, and plasma expanders, as well as cardiorespiratory support, must be readily available.
  • Test for sensitivity.
    • Skin testing is not needed for the administration of CroFab.
    • Pretreatment with epinephrine, H₁-receptor antagonists, and H₂-receptor antagonists, or corticosteroids is not routinely recommended unless the patient has a history of hypersensitivity.
  • Start the infusion.
    • Dosing is based on estimated venom injected; no dose adjustment is required for children.
    • Each vial of CroFab is reconstituted with 10 mL of sterile water for injection.
    • After reconstitution, the entire dose (4–6 vials) is diluted in 250 mL of 0.9% sodium chloride and mixed by swirling gently.
    • Use reconstituted and diluted product within 4 hours.
    • Dose should be infused intravenously over 60 minutes with careful observation for allergic or anaphylactoid reactions.
  • Repeat infusion.
    • If initial control is not achieved, the loading dose of 4–6 vials should be repeated until initial control of envenomation syndrome has been achieved.
    • After initial control has been achieved, giving additional 2-vial doses every 6 hours for 3 doses is recommended.
    • Additional doses may be necessary, as guided by clinical status and consultation with a clinician experienced in treating snakebite or a regional poison control center.
• CroFab is administered with the goal of achieving initial control, defined as the reversal or marked attenuation of all effects of venom.
  • This process encompasses 3 general areas.
    • Coagulation abnormalities
    • Systemic effects
    • Local effects (progression of swelling)
  • Volume depletion should be aggressively treated before initiating antivenin therapy because of the risk of rapid vasodilatation and third-space fluid loss associated with anaphylaxis.
  • Anaphylaxis associated with antivenin therapy should be treated in the standard manner.
• Antivenom use in copperhead bites
  • Envenomations by copperheads are not considered to be as serious as rattlesnake or cottonmouth bites.
  • Clinically significant local effects may occur, suggesting that these bites should be cautiously managed.
  • Copperhead victims treated with CroFab had marked improvement in local tissue effects, but clinical failures and recurrence of local effects also occurred.
  • The use of CroFab in copperhead bites has been shown to halt local tissue effect.
    • More data are needed to define the role of CroFab for treatment of copperhead envenomation.
    • The suggested dosing of CroFab in copperhead envenomation is a single loading dose.
    • Additional maintenance doses after initial control did not reduce incidence of recurrent swelling in 1 study.
    • After administering the loading dose, monitor patient for progressive swelling, coagulopathy development, and systemic effects.
    • The need for additional antivenin should be evaluated on a case-by-case basis, and poison control center consultation is advised.
• Antivenom use in children
  • CroFab use in children 14 months to 13 years of age has been found to be safe and effective.
  • Children with crotaline envenomation may be more likely to experience serious effects as a result of the larger ratio of venom to serum volume.
  • Any child with a crotaline envenomation that meets the criteria for antivenin therapy should receive the same dosing regimen as adults.
  • Weight-based dosing is not appropriate for antivenin neutralization because the dose should reflect venom load, not patient size.
• Additional therapeutic measures
  • Pain control
    
    • Adequate pain control allows rehabilitation to begin as early as possible to prevent contractures.
    • Opioid analgesics should be used cautiously if the venom is known to have neurotoxicity (eg, Mojave rattlesnake).
    • Nonsteroidal antiinflammatory agents should be used with caution, especially in patients with evidence of coagulopathy.
  • Infection control
    • Infection is rare in the absence of severe necrosis.
    • Good wound care is usually sufficient to prevent secondary infection.
    • Antibiotic prophylaxis is not currently suggested.
  • Corticosteroids
    • They should not be routinely administered to snakebite victims.
    • They are efficacious in patients who develop serum sickness after antivenin administration.
  • Tetanus prophylaxis
    • Clostridium tetani are not part of the mouth flora of snakes.
    • Updating the patient’s tetanus immunization is the only necessary intervention.

Coral snakes

• First aid
  • Do not use cryotherapy, incision and suction (including the Sawyer extractor), or constricting bands.
  • Australian pressure mobilization technique has been used.
    • Wrapping the entire bitten extremity with a crepe bandage, elastic bandage, or article of clothing as tightly as possible, then splinting it
• Use of antivenin
  • Antivenom effective against Eastern and Texas coral snake venom is used if a patient has definitely been bitten or if any signs or symptoms develop.
  • Guidelines are based on the judgment that risks of intravenous hyperimmune horse serum are offset by potential prevention of respiratory paralysis if therapy is not immediately administered.
  • Skin testing is of little benefit in making therapeutic decisions.
  • 3–5 vials of antivenin are mixed in 250–500 mL of normal saline, and 1–2 mL is given intravenously over 3–5 minutes.
  • The medical team must be prepared for anaphylaxis and have necessary drugs and equipment at bedside.
  • If the patient does not show any signs of an allergic reaction, then the remainder of the solution is infused slowly as tolerated.
  • An additional 3–5 vials of antivenin-saline mixture may be infused if signs and symptoms do not abate.
  • >10 vials of antivenin are rarely required for coral snake envenomations.
• Additional therapeutic measures
  • Prophylaxis for infection and tetanus as for pit viper bites is not indicated.
  • Additional measures may become necessary if aspiration pneumonia develops.
  • Patients should be aware that muscular weakness may persist for 3–6 weeks.
• Supportive therapy
  • Elective intubation before impending respiratory paralysis tends to prevent aspiration pneumonia and should be performed if any signs of bulbar paralysis develop.
  • Patient should receive cardiac and pulse oximetry monitoring (if not intubated), and intravenous access should be established.

Nonindigenous snakes

• If a bite from an exotic species is suspected, the suggested approach includes:
  • Local wound care
  • Supportive care
  • Consultation with experts at a regional poison control center

• Hymenoptera
  • Severe systemic allergic reactions or severe systemic reactions caused by massive envenomation

• Loxosceles (brown recluse spider)
  
  • Secondary infection requiring intravenous antibiotics
  • Inability to provide adequate wound care at home
  • Severe systemic symptoms

• Latrodectus (black widow spider)
  
  • Severe systemic symptoms
  • After use of antivenin

• Tarantulas
  • Significant comorbidity
  • Inability to tolerate oral fluids

• Scorpions
  • Cardiac or neurological toxicity
  • Severe systemic signs or symptoms

• Pit vipers
  • Chance of envenomation

• Coral snakes
  • Chance of envenomation
  • All victims of potential coral snake envenomation should be admitted to an intensive care unit and monitored closely for a minimum of 12 hours.
    • Effects of envenomation may develop precipitously hours after a bite and are not easily reversed once they occur.
  • If the snake cannot be found, then victims of bites suspected to be from coral snakes should be admitted to the hospital for 12 hours of observation.

• Concerns about allergic reactions, mostly from insects, result in referrals to allergy and immunology specialists.

• Hymenoptera
  • Children who experience extracutaneous systemic reactions should be referred to an allergist for risk analysis and possible venom immunotherapy.

• Fire ants
  • Patients who have experienced severe allergic reactions to stings should be referred to an allergist or immunologist for venom immunotherapy assessment.

• Loxosceles (brown recluse spider)
  
  • Surgical intervention necessary for wound care

• Latrodectus (black widow spider)
  
  • Before administration of antivenin

• Tarantulas
  • Hairs in eyes that are not easily removed

• Scorpions
  • Considered use of antivenin

• Pit vipers
  • Considered use of antivenin
  • Surgical intervention necessary for wound care

• Coral snakes
  • Patients who experience full-thickness tissue damage may require referral to a surgeon.
  • Physical or occupational therapy may be needed to encourage joint mobilization of the affected extremity.
  • Anticipated need for airway control or intensive care unit monitoring

Hymenoptera

• Patients with systemic reactions who respond completely to therapy in the emergency department should be observed for 6–8 hours after the sting for a possible delayed anaphylactic episode.
• Patients with severe symptoms, including airway, cardiovascular, or pulmonary compromise, or persistent symptoms should receive a short course of corticosteriods.
• At the time of discharge after a systemic reaction, all patients should be given a prescription for a self-administered epinephrine kit.
  • Patient or caretaker should be instructed in its proper use before discharge from the emergency department.
  • They should be encouraged to wear a Medic Alert bracelet indicating allergy to insect stings.
• Patients should be taught how to prevent further stings.
• The perception that children generally outgrow Hymenoptera sting allergies is not always true.

Snakes

• After pit viper envenomation, all patients should be observed in the emergency department for a minimum of 8 hours.
  • Patients who remain asymptomatic and whose coagulation study results are normal may be discharged with instructions to return if symptoms develop.
  • Symptomatic patients and all patients treated with antivenin should be admitted to the intensive care unit.
• Preservation of joint mobility and muscle strength is a goal after pit viper envenomation.
  • Pain control may be needed in the weeks after discharge.
  • If the patient received antivenin, then serum sickness should be discussed.
    • The patient should be taught how to monitor for this syndrome.

Winged Hymenoptera

• Severe neuroophthalmic complications include:
  • Optic neuritis
  • Loss of vision
  • Cataracts
• Respiratory and cardiovascular complications are observed more often in adults than children.
• In rare cases, serum sickness, vasculitis, encephalopathy, neuritis, and renal disease with or without rhabdomyolysis have been observed.
• Renal failure or death may occur when 20–200 wasp stings or 150–1000 or more honeybee stings have been inflicted.

Fire ants

• Secondary bacterial infections from excoriation and open erosions are not uncommon after fire ant stings.
  • These infections are usually minor and localized.
• Sepsis may result from superinfected lesions.

Snakes

• Shock
  • Patients may have a marked decrease in intravascular volume as a result of:
    • Hemorrhage
    • Third-space fluid loss
    • Vomiting
    • Diaphoresis
  • Crystalloid replacement should begin immediately in envenomated patients.
  • In the case of hypotension caused by extravascular fluid shifts or hemorrhage, antivenin therapy should be considered.
• Fluid and electrolyte abnormalities
  • May be caused by extensive third-space fluid loss
  • Electrolyte and urine output monitoring with fluid and electrolyte replacement with crystalloid is essential.
• Hematologic complications
  • Treatment of thrombocytopenia and anemia (caused by hemolysis) may require multiple transfusions.
  • Transfusions of fresh-frozen plasma and cryoprecipitate may be required in severely envenomated patients.
  • Therapy with blood products is rarely effective in the absence of antivenin therapy.
  • Treatment with coagulation factors may worsen coagulopathy by adding more substrate for unneutralized venom, thus increasing the levels of degradation products, which are also anticoagulants.
  • Thrombocytopenia often corrects with antivenin therapy alone, and clotting factor levels rarely improve when blood products are provided without antivenin.
  • Disseminated intravascular coagulopathy caused by snakebite does not respond to heparin; antivenin is the treatment of choice.
• Recurrence phenomena
  • Worsening status caused by return of venom effect after it has been successfully abated with antivenin
  • Local recurrence is return of swelling after initial control is achieved.
  • Coagulopathic recurrence is return of thrombocytopenia or hypofibrinogenemia after initial control is achieved.
    • All CroFab recipients should be reevaluated at least once during the 5 days after antivenin treatment.
    • The decision to administer additional antivenin in patients who develop delayed coagulopathy must be made on a case-by-case basis.
  • An isolated hematologic abnormality after envenomation poses a low risk for significant bleeding.
  • Multicompartment coagulopathies (critically abnormal INR, activated partial thromboplastin time, fibrinogen, platelets) may represent a risk for bleeding and may warrant additional antivenin consideration.
  • Conservative management for this scenario may be adequate; clinicians should consult with someone experienced in treating crotaline envenomations or with a regional poison control center.
• Serum sickness
  • Delayed reactions to antivenin are thought to be the result of serum sickness–like reactions attributable to immune complexes due to an immune response against antivenin proteins.
  • May occur 7–21 days after completion of treatment
  • Few patients require hospitalization.
  • Oral corticosteroids (prednisone) should be prescribed at the first signs (usually urticaria and pruritus) and should be continued for 24 hours after all symptoms have subsided and then tapered over 72 hours.
  • If necessary, diphenhydramine or hydroxyzine may be added to control pruritus.

Hymenoptera

• Do not disturb nests or hives—have someone else remove them.
• Do not wear perfume, cologne, scented sunscreens, or hairspray when outdoors.
• Use footwear when outside.
• Avoid garbage sites, orchards, fields of clover, and flowerbeds.
• Be extra careful when gardening, and cover the hands and body.
• For patients receiving immunotherapy, avoid trips outdoors if medical help is not readily available or until maintenance immunotherapy is established.
• Install screens on windows and doors to prevent insects from entering the home.

Spiders

• Prevention is mostly focused on caution in areas inhabited by spiders.
• A clean house greatly decreases the risk of spider bite.
• Wear long-sleeved shirts and gloves when outside gardening or long pants tucked into socks when hiking.
• Insect repellents that contain meta-N,N-diethyltoluamide (DEET) or picaridin offer some protection.

Snakes

• Children should not approach, disturb, play with, capture, or kill any snake.
• Snakes frequently can be found under rocks, boulders, fallen trees, fences, rubbish piles, and boats that have been left on shore for several hours; in tall grass and heavy underbrush; or sunning themselves on logs, boulders, trees, walls, or cliffs.
• The striking distance of a snake is roughly half its length.
• The striking reflex remains intact for up to 1 hour after the snake has died.
• Rattlesnakes are nocturnal feeders and are active after dark.
  • Never gather firewood after dark.
  • Camp should be set up on open ground.
  • Camp should not be set up near wood, rubbish piles, swampy areas, or the entrance of a cave.
• Once someone is bitten, everyone present should get away from the snake as quickly as possible.
  • The benefit of identifying the snake is small compared with the risk of additional bites.

• 2005 Annual Report of the American Association of Poison Control Centers’ National Poisoning and Exposure Database (other), American Association of Poison Control Centers