Burton Bentley II
WASPS, BEES, AND STINGING ANTS (HYMENOPTERA)
EPIDEMIOLOGY
More fatalities result from stings by Hymenoptera than by stings or bites by any other arthropod.
CLINICAL FEATURES
Wasps, bees, and stinging ants are members of the order Hymenoptera. Both local and generalized reactions may occur in response to an encounter.
Most allergic reactions from Hymenoptera occur from Vespidae (wasp, hornet, and yellow jacket) stings.
Local reactions consist of pain, erythema, edema, and pruritus at the sting site. Local reactions cause no systemic symptoms.
Severe local reactions increase the likelihood of serious systemic reactions in the event of recurrent envenomation.
Toxic reactions are a nonantigenic response to multiple stings. They have many of the same features of true systemic (allergic) reactions, but there is a greater frequency of gastrointestinal disturbances. Bronchospasm and urticaria do not occur.
Systemic or anaphylactic reactions are true allergic reactions that range from mild to fatal. In general, the shorter the interval between the sting and the onset of symptoms, the more severe the reaction.
Initial symptoms of anaphylaxis consist of itchy eyes, urticaria, and cough. As the reaction progresses, patients may experience respiratory failure and cardiovascular collapse.
The majority of anaphylactic reactions occur within the first 15 minutes and nearly all occur within 6 hours. There is no correlation between a systemic reaction and the number of stings.
Delayed reactions may appear 10 to 14 days after a sting. Symptoms of delayed reactions resemble serum sickness and include fever, malaise, headache, urticaria, lymphadenopathy, and polyarthritis.
EMERGENCY DEPARTMENT CARE AND DISPOSITION
The treatment of all Hymenoptera encounters is the same. Remove retained stingers and cleanse all wounds.
Erythema and swelling seen in local reactions may be difficult to distinguish from cellulitis. As a general rule, infection is present in a minority of cases.
For minor local reactions, oral antihistamines and analgesics typically suffice.
Treat severe reactions with 1:1000 epinephrine intramuscularly (IM); 0.3 to 0.5 mL for an adult and 0.01 mL/kg for a child (0.3 mL maximum). Some patients may require a second dose in 10 to 15 minutes.
Parenteral H1- and H2-receptor antagonists (eg, diphenhydramine and ranitidine) and steroids (eg, methylprednisolone) should be rapidly administered.
Bronchospasm responds to courses of inhaled β-agonists (eg, albuterol).
Hypotension should be treated aggressively with crystalloid, although dopamine and epinephrine infusions may be required.
Patients with minor symptoms who respond to conservative measures may be discharged after monitoring for several hours. Patients with severe reactions require hospitalization.
All patients with Hymenoptera reactions should be prescribed a premeasured epinephrine injector (EpiPen) and referred to an allergist for further evaluation.
SPIDERS, SCABIES, CHIGGERS, AND SCORPIONS (ARACHNIDA)
BROWN RECLUSE SPIDER (LOXOSCELES RECLUSA)
CLINICAL FEATURES
The bite of the brown recluse causes an erythematous lesion that may become firm and heal over several days to weeks.
Occasionally, a severe reaction with immediate pain, blister formation, and bluish discoloration may occur. These lesions often become necrotic over 3 to 4 days.
Loxoscelism is a systemic reaction that may occur 1 to 2 days after envenomation. Signs and symptoms include fever, chills, vomiting, arthralgias, myalgias, petechiae, and hemolysis; severe cases progress to seizure, renal failure, disseminated intravascular coagulation (DIC), and death.
The diagnosis of envenomation is made on clinical grounds since the bite is often unwitnessed.
EMERGENCY DEPARTMENT CARE AND DISPOSITION
Treatment of a brown recluse spider bite includes routine wound care, tetanus prophylaxis, and analgesics. Antibiotics may be offered when appropriate. Currently, there is no commercially available antivenin.
Most wounds heal without intervention. Surgery is reserved for lesions greater than 2 cm in size and is deferred for 2 to 3 weeks following the bite.
The role of dapsone (50-200 milligrams per day) and hyperbaric oxygen has recently been challenged, but these may prevent some ongoing local necrosis.
Patients with systemic reactions and hemolysis must be hospitalized for consideration of blood transfusion and hemodialysis.
HOBO SPIDERS (TEGENARIA AGRESTIS)
The hobo spider bite causes clinical signs and symptoms that are quite similar to those of the brown recluse spider bite.
The skin site is initially painless before developing induration, erythema, blistering, and necrosis. Victims also may experience headache, vomiting, and fatigue.
There is no specific diagnostic test or therapeutic intervention for hobo spider bites. Surgical repair may be required, although it must be delayed until the necrotizing process is complete.
BLACK WIDOW SPIDER (LATRODECTUS MACTANS)
CLINICAL FEATURES
Black widow spider bites induce an immediate pinprick sensation that often allows the victim to identify the offending spider.
Within 1 hour, the patient may experience erythematous skin lesions (often target-shaped), swelling, and diffuse muscle cramps.
Large muscle groups are involved, resulting in painful cramping of the abdominal wall musculature that may mimic peritonitis. Severe pain may wax and wane for up to 3 days, but muscle weakness and spasm can persist for weeks to months.
Serious acute complications include hypertension, respiratory failure, shock, and coma.
EMERGENCY DEPARTMENT CARE AND DISPOSITION
Initial therapy includes local wound treatment and supportive care. Analgesics and benzodiazepines relieve cramping and pain.
Severe envenomation may necessitate hospitalization for parenteral pain medication and antivenin therapy.
A commercially available horse-derived antivenin is rapidly effective for severe envenomation. The package insert provides dosing instructions. Following antivenin treatment, patients may be observed and discharged if they are asymptomatic.
TARANTULAS
When threatened, tarantulas may flick barbed hairs into their victim. These hairs can embed deeply into the conjunctiva and cornea resulting in an inflammatory response.
Tarantulas also render a painful bite causing erythema, swelling, and local joint stiffness. The treatment is local wound care and appropriate analgesia.
Any patient complaining of ocular symptoms after exposure to a tarantula should undergo a thorough slit lamp examination.
Treatment includes topical steroids and consultation with an ophthalmologist for surgical removal of the hairs.
SCORPIONS (SCORPIONIDA)
CLINICAL FEATURES
Of all North American scorpions, only the bark scorpion (Centruroides exilicauda) of the western United States is capable of producing systemic toxicity.
Centruroides exilicauda venom causes immediate burning and stinging without any visible local injury. Systemic effects are infrequent and mainly occur at the extremes of patient age.
Findings may include tachycardia, excessive secretions, roving eye movements, opisthotonos, and fasciculations.
The diagnosis may be elusive if the scorpion is not seen. Roving eye movements are nearly pathog-nomonic. A positive “tap test” (ie, exquisite local tenderness when the area is lightly tapped) is also suggestive.
EMERGENCY DEPARTMENT CARE AND DISPOSITION
Treatment includes local wound care and reassurance to allay misconceptions about the lethality of scorpion stings.
The application of ice may provide relief of local pain. Muscle spasm and fasciculations respond promptly to benzodiazepines.
Severe toxicity warrants an immediate three-vial dose of Centruroides-specific antivenin (Centruroides Immune Fab). Patients who respond to antivenin therapy may be released.
SCABIES (SARCOPTES SCABIEI)
CLINICAL FEATURES
Scabies often localize to the interdigital web spaces, penis, and female nipple. In children, the face and the scalp are commonly affected.
Transmission is typically by direct contact.
The distinctive feature of scabies is intense pruritus with burrows. The mites form white, threadlike channels with zigzag patterns and a small gray spot at the closed end.
Associated vesicles, papules, crusts, and eczematiza-tion may obscure the diagnosis. However, in undisturbed burrows the female mite may be scraped out with a blade edge.
EMERGENCY DEPARTMENT CARE AND DISPOSITION
Treatment of adults with scabies infestation consists of a thorough application of permethrin (Elimite) from the neck down; infants may require additional application to the scalp, temple, and forehead.
Reapplication is only necessary if mites are found 2 weeks following treatment, although the pruritus may last for several weeks after successful therapy.
Oral ivermectin is an alternative treatment.
CHIGGERS (TROMBICULIDAE)
CLINICAL FEATURES
Chiggers are tiny mite larvae that cause intense pruritus.
Itchiness begins within hours, followed by a papule that enlarges to a nodule over the next 1 to 2 days. Infestation has been associated with fever and erythema multiforme.
Children who have been sitting on lawns are prone to chigger lesions in the genital area.
The diagnosis of chigger bites is based on typical skin lesions in the context of a known outdoor exposure.
EMERGENCY DEPARTMENT CARE AND DISPOSITION
Treatment consists of symptomatic relief with oral or topical antihistamines; oral steroids may be required in more severe cases.
Annihilation of the mites requires topical application of lindane, permethrin, or crotamiton.
FLEAS (SIPHONAPTERA)
Flea bites cause intensely pruritic zigzag lines, especially on the legs and waist. The lesions have hem-orrhagic puncta surrounded by erythematous and urticarial patches.
Oral antihistamines, starch baths, calamine lotion, and topical steroids relieve discomfort. If secondary infection develops, topical or oral antibiotics may be needed.
LICE (ANOPLURA)
Body lice are transmitted by direct contact with infected people or fomites (eg, clothing) and typically concentrate around the waist, shoulders, axillae, and neck. Pubic lice are spread by sexual contact. Infestation induces intensely pruritic papules and wheals.
Permethrin is the primary treatment of body lice infestation. Treatment of hair infestation requires a thorough shampoo with pyrethrin with piperonyl butoxide; reapplication is mandatory in 10 days.
Clothing, bedding, and personal articles must be sterilized in hot (>52°C) water to prevent reinfestation.
KISSING BUGS AND BEDBUGS (HEMIPTERA)
Kissing bugs (conenose beetles) and bedbugs feed on blood as they attack the exposed surface of a sleeping victim.
The initial bite is painless. Wheals, hemorrhagic papules, and bullae may follow. Anaphylaxis is common in the sensitized individual.
Treatment consists of local wound care and analgesics. Allergic reactions must be treated as previously outlined for Hymenoptera envenomation.
PIT VIPER (CROTALIDAE) BITES
EPIDEMIOLOGY
There are approximately 8000 venomous snakebites each year in the United States, but only about 10 deaths result. Twenty-five percent of bites are “dry strikes” with no effect from venom.
Except for imported species and coral snakes, the only venomous North American snakes are members of the Crotalidae family (eg, rattlesnakes, copperheads, water moccasins, and massasaugas).
Crotalid snakes, commonly known as pit vipers, are identified by their retractable fangs and by heat-sensitive depressions (pits) located between each eye and nostril.
CLINICAL FEATURES
The effects of crotalid envenomation depend on the size and species of the snake, the age and size of the victim, the time elapsed since the bite, and the characteristics of the bite itself.
The hallmark of pit viper envenomation is fang marks with local pain and swelling.
There are three classes of criteria that determine the severity of a rattlesnake bite: (1) degree of local injury (swelling, pain, ecchymosis), (2) degree of systemic involvement (hypotension, tachycardia, paresthesia), and (3) evolving coagulopathy (thrombocytopenia, elevated prothrombin time, hypofibrinogenemia). Abnormalities in any of these three areas indicate that envenomation has occurred.
Conversely, the absence of any clinical findings after 8 to 12 hours effectively rules out venom injection.
It is crucial to remember that initially benign-appearing bites may still evolve with devastating complications.
DIAGNOSIS AND DIFFERENTIAL
The diagnosis of crotalid envenomation is based on clinical findings and corroborating laboratory data.
In general, envenomated patients will have swelling within 30 minutes, although some may take up to 12 hours.
Minimal envenomation describes cases with local swelling, no systemic signs, and no laboratory abnormalities.
Moderate envenomation causes increased swelling that spreads from the site. These patients also may have systemic signs such as nausea, paresthesia, hypotension, and tachycardia. Coagulation parameters may be abnormal, but there is no significant bleeding.
Severe envenomation causes extensive swelling, potentially life-threatening systemic signs (eg, hypotension, altered mental status, respiratory distress), and markedly abnormal coagulation parameters that may result in hemorrhage.
EMERGENCY DEPARTMENT CARE AND DISPOSITION
All pit viper bites require medical attention; first aid measures must not delay definitive care. The patient should minimize physical activity and immobilize the bitten extremity in a neutral position below the level of the heart.
Local wound care and tetanus immunization should be given, but prophylactic antibiotics and steroids have no proven benefit.
Limb circumference at several sites above and below the wound should be checked and documented every 30 minutes. The border of advancing edema should be marked.
Any patient with progressive local swelling, systemic effects, or coagulopathy should receive antivenin therapy immediately.
Polyvalent Crotalidae Immune Fab (FabAV), a sheep-derived antivenin, is administered as an initial dose of four to six vials IV; there is no need for a prior skin testing.
The initial dose of FabAV is infused IV over 1 hour. Since allergic reactions may occur, the infusion should proceed at a slow rate of 25 to 50 mL/h for the first 10 minutes. If the patient remains stable, the infusion rate may be increased to the full 250-mL/h rate.
Since the goal of therapy is to neutralize existing venom, dosing regimens are exactly the same for both children and adults (although the amount of diluent will need proper adjustment).
One hour after the initial dose has been administered, the patient must be reexamined to determine if local swelling has been arrested, coagulation tests have normalized, and systemic symptoms have abated. If the initial dose was ineffective in any of these three areas, then a repeat dose of four to six vials should be administered.
Laboratory determinations are repeated every 4 hours or after each course of antivenin, whichever is more frequent.
Since the end point of antivenin therapy is the arrest of progressive symptoms and coagulopathy, the administration of antivenin must continue until complete control of the envenomation is achieved.
Once initial control has been achieved, the protocol is completed by administering additional two-vial doses every 6 hours for a total of three more doses.
Compartment syndrome (pressure >30 mm Hg) may occur secondary to envenomation. Repeated dosing of antivenin is the most effective therapy for elevated compartment pressures. Limb elevation, IV mannitol, and surgical fasciotomy may be required.
The mainstay of coagulopathy remains antivenin therapy. Severe active bleeding due to coagulopathy may require additional transfusion of blood products.
Any patient with a pit viper bite must be observed for at least 8 hours. Patients with no evidence of envenomation after 8 to 12 hours may be discharged.
Serum sickness occurs in 5% of patients within 1 to 2 weeks of FabAV therapy. Oral prednisone is the standard treatment.
CORAL SNAKE BITE
CLINICAL FEATURES
True coral snakes have a yellow band directly touching a red band; nonpoisonous impostors have an intervening black band. This distinctive pattern establishes the mnemonic for North American snakes: “Red on yellow, kill a fellow; red on black, venom lack.”
Only the bite of the eastern coral snake (Micrurus fulvius fulvius) requires significant treatment; the bite of the Sonoran (Arizona) coral snake is mild and only needs local care.
Eastern coral snake venom is a potent neurotoxin capable of causing tremor, salivation, respiratory paralysis, seizures, and bulbar palsies (eg, dysarthria, diplopia, and dysphagia).
EMERGENCY DEPARTMENT CARE AND DISPOSITION
Patients with possible envenomation must be admitted to the hospital for 24 to 48 hours of observation. In the absence of antivenin therapy, the toxic effects of coral snake venom are not easily reversed.
The manufacture of coral snake antivenin has ceased and current lots are expiring. If treatment is required, immediately contact a poison control center for current information on availability.
GILA MONSTERS
Gila monsters are slow-moving poisonous lizards that are indigenous to the desert of the southwestern United States.
Gila monsters have a tenacious bite and may be difficult to remove from the bitten extremity.
Most bites result in local pain and swelling that worsens over several hours before subsiding.
Patients rarely experience systemic toxicity, including weakness, lightheadedness, paresthesia, diaphoresis, or severe hypertension.
Treatment involves removal of the reptile from the bite site. The Gila monster often will loosen its grip when no longer suspended in midair. Other reported methods include submersion, cast spreaders, or application of an irritating flame.
The only requisite treatment is local wound care and a careful search for implanted teeth.
For further reading see Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 7th ed., see Chapter 205, “Bites and Stings,” by Aaron B. Schneir and Richard F. Clark, and Chapter 206, “Reptile Bites,” by Richard C. Dart and Frank F. S. Daly.