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Hymenoptera Stings

Author: Paul A Janson, MD, Instructor, Tufts University School of Medicine; Director, EMT/RN Consultants; Consulting Staff, Department of Emergency Medicine, Lawrence General Hospital
Coauthor(s): Richard Iseke, MD, Assistant Professor, Department of Emergency Medicine, University of Massachusetts School of Medicine
Contributor Information and Disclosures

Updated: Nov 8, 2007

Introduction

Background

In the United States alone, anaphylaxis accounts for approximately 500 deaths each year and significant morbidity. Hymenoptera envenomation is a major contributor to these statistics.

The order Hymenoptera includes bees, hornets, wasps, yellow jackets, and ants. More than 14,000 species are represented. Honeybees and bumblebees belong to the Apidae family, while hornets, wasps, and yellow jackets belong to the Vespidae family. Ants belong to the family Formicidae.

Among winged Hymenoptera, envenomation is used for killing or paralyzing prey and for defense. The stinger, therefore, is used repeatedly. Only the honeybee leaves the stinger, venom gland, and other internal organs attached at the site of the sting.

Hymenoptera are present on all land areas of the world, except the polar regions, during some or all seasons. In Africa, domesticated honeybees have been crossed with more aggressive wild honeybees. These Africanized bees (Apis mellifera scutellata) have been introduced into South America and, from there, have migrated to North America, including the southern United States. Their venom is no more potent than that of other honeybees, but they are more aggressive and tend to swarm, causing multiple stings.

Fire ants (Solenopsis invicta) also are present in the southern United States, having migrated from South America. In Florida and Louisiana, they have replaced many of the indigenous species.

Pathophysiology

The venom of winged Hymenoptera contains over 30 individual compounds. These include biogenic amines (eg, acetylcholine, dopamine, histamine, norepinephrine, serotonin), polypeptides or protein toxins (eg, apamin, melittin, kinins), and enzymes (eg, hyaluronidase, phospholipases). The venom of fire, or stinging, ants consists of small amounts of low molecular weight protein and is as much as 95% alkaloid, which is uncommon in ant species.

Reactions to envenomation may be directly toxic, either local or systemic, or allergic, either localized or anaphylactic. Allergic reaction to fire ant venom is unusual. Strong cross-reactivity to the allergic reactions occurs within a family, but less so between families. The venom of bees and wasps has been reported to be more potent during the autumn months.

Frequency

United States

Hymenoptera envenomation affects nearly every person during his or her lifetime and 10-20% of the population annually. From 300-500 deaths occur annually, almost all are secondary to anaphylaxis.

International

The international incidence of Hymenoptera envenomation is related to region and local custom. In Africa, the harvesting of honey involves collecting honey from wild bees, which usually involves destroying the hive and results in subsequent exposure to hundreds of bees. In traditional Chinese herbal medicine, apiotherapy involves mixing bee venom with ointment and applying it to the skin or eyes, which may result in allergic reactions.

Age

Children with a history of severe reaction may have only slightly higher risk of anaphylaxis when they reach adulthood compared to the general population, while history of severe reaction as an adult is associated with a rate of anaphylaxis of approximately 60%.

Clinical

History

Clinical presentation following envenomation by Hymenoptera species follows 3 basic patterns.

• First and most common is the simple sting or local reaction, which initially results in localized swelling and pain, with pruritus following a few hours later. The swelling may increase over several days and may take as long as a week to resolve completely.
  • If the envenomation is on the hands (or in some cases on the feet if toe rings are worn), rings should be removed promptly before the swelling extends to the digits. Swelling may involve an entire extremity.
  • Large envenomations (>30-40 stings) may result in a systemic, or anaphylactoid, reaction with shock secondary to myocardial depression and vasodilation. This is the direct result of systemic absorption of venom and should be distinguished from the allergic reactions discussed below. These patients present with stupor or coma and seizures. They may develop other complications of shock, including metabolic acidosis and organ failure, particularly acute renal failure.
• The second type of presentation is the immediate hypersensitivity reaction, or generalized reaction/anaphylaxis. It may manifest as local swelling or urticaria with pain and itching. It also may spread to become more generalized, with urticaria and itching.
  • The reaction may progress to involve the upper or lower airway in an anaphylactic reaction. If anaphylaxis develops, it usually presents within 1-2 hours but may be delayed for as long as 4-6 hours. Patients treated for anaphylaxis may have recurrent symptoms as long as 48 hours after successful initial treatment.
  • These patients may present with acute airway obstruction due to laryngeal edema or bronchoconstriction with respiratory failure, and early endotracheal intubation or cricothyroidotomy may be necessary. Such patients may not be able to give a history at the time of presentation. If patients present awake and alert, more conservative treatment may be successful, but the clinician is advised to take symptoms such as hoarseness or shortness of breath seriously even in the absence of clinical signs.
  • Early in the treatment of patients presenting with severe local or systemic reaction, while they still are able to provide information, questioning them about their medical history, including medication and allergies, is a wise practice.
  • Patients with a previous history of severe local reactions have a 5% chance of anaphylaxis in the future, while those with generalized systemic reactions have 60% chance of anaphylaxis upon future exposure. More recent and more severe previous reactions are associated with increased risk; however, most patients who die of anaphylaxis give no history of prior severe local or generalized reaction.
• Finally, patients may present with delayed hypersensitivity reactions. These may be immune-complex mediated (either immunoglobulin M or immunoglobulin G) and may be systemic (serum sickness type) or local (Arthus type).
  • Presentation usually is within 1 week of envenomation, but often the history of an insect bite or sting is not volunteered by the patient unless the clinician specifically asks.
  • The symptoms may include fever, arthralgias and myalgias, headache, and general malaise. Signs include rash (either maculopapular or palpable purpura of vasculitis), joint swelling and tenderness with or without effusions, adenopathy, and evidence of glomerulitis or nephrotic syndrome. Necrotizing vasculitis also may be evident.
• Several syndromes, presumed to be immune-mediated, are associated with late complications of Hymenoptera envenomation, including hemolytic anemia, thrombocytopenic purpura, Guillain-Barré syndrome, multiple sclerosis, optic neuritis, Parkinsonism, and transverse myelitis.
• At least 1 case of M ü nchausen syndrome has been reported, in which a patient with known allergy to aspirin took this drug in order to mimic anaphylaxis from Hymenoptera envenomation.¹
• The stings of fire ants usually are multiple.
  • The presentation usually is that of swelling and pain with early vesicle formation, followed by ulceration and possible secondary infection.
  • Local reactions are the rule, and allergic manifestations, either immediate or delayed, are uncommon.

Physical

• In the presence of a local reaction, one should expect to find local swelling and tenderness at the site(s) of envenomation, but the presence of urticaria may suggest a more generalized reaction.
  • The airway should be accessed in all patients, particularly those with stings to the face or generalized urticaria.
  • Frequently, auscultation of the lungs for the presence of wheezing is advisable, with prompt therapy initiated and reassessed until improvement is noted. If airway involvement is present, an anaphylactic reaction should be considered.
• The physical findings in cases of anaphylactoid reactions resulting from large venom loads are shock with hypotension secondary to vasodilation and myocardial depression. A bradycardia may be present. Stupor or coma is common.
• The physical examination findings in cases of immediate hypersensitivity usually include urticaria and swelling at the site of the sting, which frequently is generalized.
  • Patients often are anxious, but true confusion or stupor should suggest impending respiratory arrest or vascular collapse.
  • Vital signs often show tachycardia and hypertension in addition to an increase in the respiratory rate. The absence of such findings in a patient in obvious distress should suggest impending collapse that requires aggressive intervention.
  • Signs of upper airway obstruction with stridor or lower tract involvement with wheezing may be present.
  • Intercurrent medications, particularly beta-blockers, may mask the signs of anaphylaxis and may complicate its treatment.
  • Both severe systemic reactions and anaphylactic reactions may be complicated acutely by myocardial infarction or stroke and should be investigated further if symptoms suggest these possibilities.
• The physical findings in patients with delayed hypersensitivity are those of the particular syndrome at presentation.
  • Joint effusions and inflammation (serum sickness), palpable purpura (vasculitis), edema or congestive heart failure (renal failure or nephrotic syndrome), and jaundice or bruising (hemolytic anemia or thrombocytopenia) are examples.
  • Neurologic syndromes vary greatly in their specific findings.

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