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Venomous insects are grouped into four families of the order Hymenoptera: Apidae (honeybees), Bombidae (bumblebees), Vespidae (wasps, hornets, and yellow jackets), and Formicidae (ants). With the exception of Vespidae, most Hymenoptera sting only when disturbed or when the hive is threatened. Yellow jackets and other vespids may attack without provocation and are the most common cause of insect-induced anaphylactic reactions.

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  1. Mechanism of toxicity. The venoms of Hymenoptera are complex mixtures of enzymes and are delivered by various methods. The venom apparatus is located in the posterior abdomen of the female.

    1. The terminal end of the stinger of the Apidae (honeybees) is barbed, so the stinger remains in the victim and some or all of the venom apparatus is torn from the body of the bee, resulting in its death as it flies away. The musculature surrounding the venom sac continues to contract for several minutes after evisceration, causing venom to be ejected persistently. The Bombidae and Vespidae have stingers that remain functionally intact after a sting, resulting in their ability to inflict multiple stings.

    2. The envenomating Formicidae have secretory venom glands in the posterior abdomen and envenomate either by injecting venom through a stinger or by spraying venom from the posterior abdomen into a bite wound produced by their mandibles.

  2. Toxic dose. The dose of venom delivered per sting may vary from none to the entire contents of the venom gland. The toxic response is highly variable, depending on individual sensitivity. Some Hymenoptera, such as wasps, have the ability to sting several times, increasing the venom load. Africanized bee attacks may result in over 1000 stings. Disturbing a fire ant nest may result in as many as 3000–5000 stings within seconds.

  3. Clinical presentation. The patient may present with local or systemic signs of envenomation or an allergic reaction.

    1. Envenomation. Once venom is injected, there is usually an immediate onset of severe pain, followed by a local inflammatory reaction that may include erythema, wheal formation, ecchymosis, edema, vesiculation and blisters, itching, and a sensation of warmth. Multiple stings, and very rarely severe single stings, may also produce vomiting, diarrhea, hypotension, syncope, cyanosis, dyspnea, rhabdomyolysis, coagulopathy, and death.

    2. Allergic reactions. Numerous deaths occur annually in the United States from immediate hypersensitivity (anaphylactic) reactions characterized by urticaria, angioedema, bronchospasm, and shock. Most anaphylactic reactions occur within 15 minutes of envenomation. Rarely, delayed-onset reactions may occur, including Arthus reactions (arthralgias and fever), nephritis, transverse myelitis, and Guillain-Barré syndrome. Cross-sensitivity to fire ant venom can exist in some patients with Apidae or Vespidae allergies.

  4. Diagnosis is usually obvious from the history of exposure and typical findings.

    1. Specific levels. Not relevant.

    2. Other useful laboratory studies. Creatine kinase (CK), the CK-MB isoenzyme, cardiac troponin T or I, and renal function should be checked in severe cases of multiple stings.

  5. Treatment

    1. Emergency and supportive measures

      1. Monitor the victim closely for at least 30–60 minutes.

      2. Treat anaphylaxis (See Anaphylactic and anaphylactoid reactions), if it occurs, with epinephrine (See Epinephrine) and diphenhydramine ...

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