Hymenoptera stings account for more deaths in the United States than any other envenomation. Order Hymenoptera includes Apis species, ie, bees (European, African), vespids (wasps, yellow jackets, hornets), and ants. Although most deaths result from immunologic mechanisms, some are from direct toxicity. Severe anaphylactoid reactions occur occasionally when toxins directly stimulate mast cells. While the vast majority of stings cause only minor problems, stings cause a significant number of deaths.
Pathophysiology: Target organs are the skin, vascular system, and respiratory system. Pathology is similar to other immunoglobulin E (IgE)–mediated allergic reactions. Urticaria, vasodilation, bronchospasm, laryngospasm, and angioedema are prominent symptoms of the reaction. Respiratory arrest may result in refractory cases.
Frequency:
In the US: Ants sting 9.3 million people each year. Other Hymenoptera account for more than 1 million stings annually.
History:
A patient's reaction to a Hymenoptera sting determines the treatment required. Reactions may be graded as local, urticaria without systemic symptoms, and generalized. Emergency physicians should attempt to determine degree of reaction based on both patient history and a physical examination.
Rapid onset of symptoms is the rule; 50% of deaths occur within 30 minutes of the sting, and 75% occur within 4 hours.
Fatal allergic reactions can occur as the first generalized reaction. Far more common, however, is a fatal reaction following a previous, milder generalized reaction. The shorter the interval since the last sting, the more likely it is that a severe reaction will take place.
Large local reactions do not predispose patients to generalized reactions. Local reactions may be life threatening if local swelling at the sting site compromises the airway. Local reactions to stings can cause peripheral nerve block.
Local reactions may produce the following:
Pain occurs immediately after sting.
Edema is marked and may extend to 10 cm from site of envenomation.
The insect frequently is seen by patient and may be identified from the description.
Bleeding may occur at site of sting.
Pruritus is common.
Vasodilation may produce a sensation of warmth.
The stinging apparatus may have been seen in the wound and removed prior to presentation.
Nausea or vomiting may occur without generalization.
Visceral pain may occur with stings in the gastrointestinal (GI) tract after ingestion of the insect.
Urticaria may occur with or without the symptoms noted in local reaction.
Generalized reactions may produce the following symptoms:
Urticaria
Confluent red rash
Shortness of breath, wheezing
Edema in airway, tongue, or uvula
Weakness, syncope
Anxiety, confusion
Chest pain
Physical:
Local reactions may include the following:
Erythema, edema, warmth, tenderness
Drainage from site of sting
Compromised distal circulation as result of edema
Distal sensation loss from stings over peripheral nerve
Corneal ulceration from corneal stings
With bee stings, stinging apparatus visible at sting site
Ant stings: Vesicles from fire ants, classic arc of fire ant stings, and ant stings on mucous membranes or conjunctival surfaces cause dramatic swelling in patients who are sensitive.
Urticaria or generalized redness may develop without systemic symptoms.
Generalized reactions may include the following symptoms:
Urticaria
Vomiting
Wheezing
Tachypnea
Hypotension
Laryngoedema, lingular edema, uvular edema
Delirium, shock
Respiratory arrest
Causes:
Hymenoptera are social creatures that typically sting to protect their colony, nest, or hive. Most stings are incited by proximity to the colony. Noisy or vigorous activity (eg, lawn mowers, weed eaters), bright or dark colors, and perfumes also may incite stings. In addition, these insects can release defense pheromones that attract other insects and induce them to sting. These pheromones are released during stinging or when an insect is smashed. Hymenoptera frequently are swallowed, and their stings can cause painful swelling in the mouth or esophagus.
Although bee and wasp venom varies from species to species, all venom is composed primarily of proteins, peptides, and amines. Toxic components include phospholipase, histamine, bradykinin, acetylcholine, dopamine, and serotonin. In addition, mast cell degranulating (MCD) peptide and mastoparan are peptides that can cause degranulation of mast cells and result in an anaphylactoid reaction. Molecule size and the presence of protein enhance the antigen properties of venom, making it a potent activator of the immune system. Most significant reactions are mediated through true IgE allergic mechanisms that activate mast cell degranulation.
Anaphylactoid reactions may occur. However, venom load may be sufficient to cause fatal injury without the added effects of the endogenous system. This may result from as few as 30 vespid stings or 200 honeybee stings. Since the compounds are similar in anaphylactic and toxic reactions, pathology and treatment also are similar.
Bees and wasps sting through a modified ovipositor. They puncture the skin with a hollow stinger and then inject venom. Bees leave their barbed stinger in the skin along with its stinging apparatus, killing the bee. Vespids have smooth or less-barbed stingers and can sting more than once. Vespids are responsible for almost twice as many allergic reactions as honeybees. Retained stingers can cause granuloma formation and subsequent epidermal necrosis.
A "killer" bee is an Africanized honeybee (Apis mellifera scutellata), the offspring of aggressive wild African honeybees and domesticated European honeybees. Aggressive defensive behavior is dominant in these offspring. This variety displays increased group defense behavior. One pheromone, isoamylacetate, has been isolated as a mediator of this activity. Africanized bees defend their hive up to a 150-yard radius, 3 times the distance of European bees.
As of May 2000, Africanized bees have migrated from their western-hemisphere origin in Brazil to Texas, Arizona, California, New Mexico, and Nevada, according to the US Department of Agriculture.
Multiple stings from these species are more common. Hymenoptera fly at only 4 mph, allowing most victims to flee after only a few stings. Overwhelming numbers of stings usually occur in young patients or in those slowed by physical limitations or intoxication.
In addition to reaction to stings, bee venom may be encountered as a result of apiotherapy. In this Chinese treatment, ointment containing bee venom may be applied to skin or eye and result in an immunologic reaction.
Ant stings
Ants account for one half of all insects. While many ant species sting, the most aggressive in the United States are imported fire ants, Solenopsis invicta. These ants fiercely guard their territory and attack intruders in large numbers, inflicting thousands of stings and bites to victims unable to escape. Fire ant venom is 95% alkaloid, which is unique among ants. A fire ant typically bites with its mandibles, then swivels its abdomen and stings repeatedly in an arc about the bite site. Their stings develop into sterile pustules and then rupture, leaving crusted wounds that may become infected secondarily. Patients have survived as many as 5000 fire ant stings. Brazilian fire ants, S invicta, have nearly eradicated native ant species in their range from Florida to Texas and north to Arkansas and South Carolina. S invicta is found in South and North America in areas where mean high temperatures are 15°C or higher.
Stings from other ants often closely resemble those of wasps and bees, although with less tissue destruction and less severity. Harvester ants, Pogonomyrmex species, inject venom containing a hemolysin. This sting frequently creates an ecchymotic area surrounding the sting site. Some species of field ants truly bite with the mandible and spray the acidic toxin into the wound without injecting venom. Formic acid, a component of ant venom uncommon in bee or wasp stings, is derived from the superfamily name Formicidae. Ant stings cause generalized reactions less often than stings from flying Hymenoptera.
Prehospital Care:
Prehospital care must assess severity immediately and provide immediate appropriate treatment, because the most endangered patients die within 30 minutes of a sting.
Local reactions can be life threatening if swelling occludes the airway. Initiate invasive measures to secure the airway if this occurs. Otherwise, the following local care measures suffice:
Diphenhydramine limits the size of the local reaction.
Clean wound and remove stinger if present.
Apply ice or cool packs.
Elevate extremity to limit edema.
Manage generalized reactions similarly to anaphylaxis, even in the absence of shock. Check airway and ventilatory status. Treatment should include an initial intravenous (IV) bolus of 10-20 mL/kg isotonic crystalloids in addition to diphenhydramine and epinephrine.
If the patient has not removed the stinger, it should be removed as soon as possible by the first caregiver on the scene. Delay increases venom load, so the fastest removal technique is the best. Pinching and traction is an acceptable technique.
Emergency Department Care:
Corticosteroids and cimetidine may be given IV; vasopressors such as dopamine can be used to provide vascular support.
Blood products may be required in the event of disseminated intravascular coagulation (DIC).
Consultations:
Refer all patients with generalized reactions to an allergist as soon as possible, because risk of fatal reaction is inversely related to length of time since the last sting.
