Spider Bite FAQ

Kyoto: Hiking from Kibune to Kurama

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Between fifty and one hundred deaths result annually from allergic reactions to Hymenoptera stings (bees, wasps, hornets, and fire ants) in the United States, more than the deaths from rabies, poisonous snakes, spiders, and scorpions combined. Approximately one of every two hundred people in the United States has experienced a severe reaction to such stings. Potentially fatal reactions can be prevented or successfully treated in individuals known to have such allergies, but many deaths still occur in persons whose allergic status had not been previously recognized. The problem of allergies and the severe, potentially lethal allergic reactions known as "anaphylactic shock" are discussed in Chapter Twenty, "Allergies."

An individual allergic to insect stings usually experiences milder allergic reactions before having a potentially fatal reaction. Two types of nonlethal reactions occur: local reactions and systemic reactions.

Local reactions are characterized b severe swelling limited to the limb or portion of the limb that is the site of the insect sting. Almost all insect stings are associated with some swelling, but the area of swelling is usually three inches (7.5 cm) or less in diameter. With severe local reactions, a major portion of an extremity, such as the entire forearm, is swollen, and may be painful, associated with itching, or mildly discolored.

Systemic reactions occur in areas of the body some distance from the site of the sting. Most typical are hives, which may be scattered over much of the body. Generalized itching or reddening of the skin may also occur. Persons with more severe reactions may have hypotension (low blood pressure) and difficulty breathing. (Clearly, the last two reactions could be fatal if severe.)

Investigators of insect hypersensitivity reactions have recommended that individuals who have had a systemic reaction to an insect sting undergo skin testing with Hymenoptera venoms. (If the results of skin tests are inconclusive, more sophisticated measurement of venom-specific IgE antibodies by the radioallergosorbent procedure can be carried out.) About half of the people who have had a systemic reaction and also have a positive skin test would be expected to have a severe, possibly fatal reaction if stung again. Desensitization with purified insect venoms—not whole-body extracts—is recommend for these individuals. (In one recent study of children who had experienced an anaphylactic reaction following a sting, only nine percent of subsequent accidental stings led to severe reactions. None of the reactions were more severe than the original reactions, which led to the conclusion that immunotherapy was unnecessary for such individuals.)

Desensitization can be a drawn-out, uncomfortable procedure but also can be life-saving. Starting with very small quantities, increasingly larger amounts of the insect venoms are injected subcutaneously until the allergic reaction is "neutralized."

Desensitization must be carried out under the close supervision of a physician experienced with the procedure. Severe, life-threatening allergic reactions to the desensitization injections may occur, and a physician must be on hand to deal with them. However, a physician who is standing by watching for a reaction can treat it effectively. Allergic reactions to insect stings in a wilderness environment without a physician in attendance are a far greater threat. Desensitization, or even skin testing, is not recommended for individuals who have large local reactions because these are rarely followed by systemic reactions. However, carrying epinephrine (adrenaline) is recommended for individuals who have had either type of reaction.

For individuals experiencing an anaphylactic reaction, 0.3 cc of a 1:1,000 solution of epinephrine should be injected subcutaneously as soon as symptoms are detected. Second (and sometimes third) injections are often needed at intervals of twelve to fifteen minutes.

Rock climbers and some other wilderness users who have systemic allergic reactions to insect stings have a unique risk of fatal reactions because they are subject to stings in locations, such as rock walls, where they can not be immediately treated by others and only with difficulty by themselves. Such persons should seriously consider desensitization now that purified venom preparations, which make that procedure so much more reliable, are available. They also must be prepared to treat an anaphylactic reaction at any time.