ENVENOMATIONS - Medicine for Mountaineering and Other Wilderness Activities - page 502

An individual allergic to insect stings usually experiences milder allergic reactions be-
fore having a potentially fatal reaction. Two types of nonlethal reactions occur: local reac-
tions and systemic reactions.
Local reactions are characterized by 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 itch-
ingorreddeningoftheskinalsooccur.Personswithmoreseverereactionsmayexperience
hypotension (low blood pressure) and difficulty breathing, either of which clearly could be
fatal if severe.
Investigators of insect hypersensitivity reactions have recommended that individuals
whohavehadasystemicreactiontoaninsectstingundergoskintestingwithHymenoptera
venoms. (If the results of skin tests are inconclusive, more sophisticated measurement of
venomspecific IgEantibodies canbecarriedout.)Abouthalfofthosewhohavehadasys-
temic reaction and also have a positive skin test would be expected to have a severe, pos-
sibly fatal reaction if stung again. Desensitization with purified insect venoms—not whole
body extracts—is recommended for these individuals. (In one study of children who had
experienced an anaphylactic reaction following a sting, only 9 percent of subsequent acci-
dental stings led to severe reactions. None of the reactions were more severe than the ori-
ginal reaction, which led to the conclusion that immunotherapy was unnecessary for such
individuals.)
Desensitizationcanbeadrawn-out,uncomfortableprocedurebutalsocanbelifesaving.
Starting with very small quantities, increasingly larger amounts of the insect venoms are
injected subcutaneously until the allergic reaction is neutralized. The individual is still al-
lergictotheHymenopteravenoms,buttheantibodiesresponsibleforproducingtheallergic
reactions are used up by the repeated injections of the material with which they react. Gen-
erally, even after successful desensitization, injections must be continued at approximately
monthly intervals for years or indefinitely. If the desensitization injections are stopped, the
former allergic condition often reappears.
Desensitization must be carried out under the close supervision of a physician experi-
enced with the procedure. Severe, life-threatening allergic reactions to the desensitization
injections occur, and a physician must be on hand to deal with them. However, a physician
watching for a reaction can treat it effectively. Allergic reactions to insect stings in a wil-
derness environment without a physician in attendance are a far greater threat.
Desensitization,orevenskintesting,isnotrecommendedforindividualswhohavelarge
local reactions because these are rarely followed by systemic reactions. However, carrying