What is A Venom Allergy?

Hymenoptera venom allergy is an immunoglobulin E (IgE)- mediated hypersensitivity to the venom of insects in the insect order Hymenoptera. This allergic reaction may be caused by stings from a number of species in this insect order, occurring only in persons who have previously been sensitized to Hymenoptera venom.

Insect sting allergy can develop at any age and usually manifests after several uneventful stings. The incidence of systemic reactions to Hymenoptera venom is approximately 3% in adults. Although children are stung more often than adults, systemic reactions occur in only about 1% of children younger than 17 years, and many of these reactions are relatively mild. Large local reactions to Hymenoptera stings are more common in children, with an estimated incidence of 20% and 10%, respectively, for children and adults. The prevalence of insect sting allergy is twice as high in male as in female patients and may be a result of increased exposure rather than inherent susceptibility. There is no clear association with other allergies, and only 30% of patients with venom allergy are atopic. In addition, insect sting allergy is statistically not more likely to occur in persons with a family history of sting reactions.

At least 50 deaths per year occur in the United States from insect sting reactions, and many other sting fatalities may be unrecognized. Approximately one half of deaths occur in victims with no history of a prior sting reaction. Most fatalities (80%) occur in adults older than 40 years, and only 2% occur in persons younger than 20 years.

What are the Signs and Symptoms?

Most Hymenoptera stings cause small local reactions of no significant medical consequence. These normal sting reactions are characterized by pain, itching, redness, and swelling at the sting site that resolve within several hours and are caused by the pharmacologic properties of the venom. Some large local reactions are caused by a late-phase IgE-dependent reaction that is mild initially but progresses after 12 to 24 hours to a diameter of more than 5 cm; these usually peak in intensity at 48 to 72 hours. These reactions are contiguous with the sting site and occasionally involve an entire extremity. In rare cases, massive swelling causes local anatomic compression. Large local sting reactions typically resolve gradually over 5 to 10 days. Virtually all patients with large local reactions continue to have similar reactions with subsequent stings. This tendency is not modified with venom immunotherapy; therefore, patients with large local reactions are not candidates for further diagnostic evaluation (see later).

Systemic reactions cause signs and symptoms in one or more organ systems and are almost always IgE-mediated. Systemic reactions cause a spectrum of manifestations, ranging from cutaneous signs (pruritus, flushing, urticaria, angioedema) to respiratory involvement (cough, throat and/or chest tightness, dyspnea, wheezing) and cardiovascular compromise (dizziness, hypotension, unconsciousness), depending on the severity of the reaction. Gastrointestinal manifestations (nausea, vomiting, diarrhea) and uterine cramping also occur occasionally. Cardiac anaphylaxis with manifestations of coronary vasospasm, arrhythmias, or bradycardia can also occur following stings, even in persons with no underlying cardiac disease. Systemic reactions usually cause signs and symptoms starting within minutes following a sting. In general, the sooner the symptoms occur, the more severe the reaction. Cutaneous signs and symptoms occur in 80% of adults and 95% of children with systemic reactions, but they are the sole manifestation of the reaction in only 15% of adults. Isolated cutaneous reactions occur in 60% of children, however, who tend to have a more benign course than adults. Although symptoms involving the upper and lower airways occur with approximately the same frequency in children and adults, children have a much lower incidence of cardiovascular manifestations

Systemic reactions also occur occasionally as a result of the toxic properties of Hymenoptera venom. They are most often associated with multiple simultaneous stings or underlying mastocytosis. These reactions may be indistinguishable from acute, systemic IgE- mediated reactions. Large numbers of stings can cause other serious reactions including rhabdomyolysis with renal failure, hemolysis, acute respiratory distress syndrome, and diffuse intravascular coagulation. Delayed reactions of unknown mechanism that rarely occur following stings include serum-sickness–like reactions, neuropathies, Guillain-Barré syndrome, myocarditis, and glomerulonephritis.

How to Diagnosis Venom Allergy?

Venom skin testing is the most sensitive form of venom testing and continues to be the benchmark used by most allergists. A large number of allergy cells or mast cells reside in the skin providing a very accessible area to diagnose venom allergies. An alternative to venom skin testing is the blood test (RAST) which has a lower sensitivity but it is very useful in patients who have had severe stinging insect reactions and may not be able to tolerate skin testing.

The forearm is the area of the skin that is typically tested by the prick method. It is first cleansed with alcohol and a pen is used to label the area in a grid-like pattern that indicates where the testing substance (allergen) is to be applied. The skin is then pricked with a small, sterile, pointed instrument containing a specific substance or allergen to which the patient may be allergic. After a waiting period of about 15 minutes, the test is read. Positive reactions on skin testing are typically a red, itchy area with a raised center that may look like a mosquito bite. Skin testing on the back is compared with negative (saline) and positive (histamine) control tests to help gauge the intensity of the reaction.

If necessary after prick skin tests, the doctor may recommend intradermal skin tests. The upper arm is the area of the skin that is typically tested. It is first cleansed with alcohol and a pen is used to label the skin in a grid-like pattern that indicates where the testing substance (allergen) is to be injected. The skin is then injected superficially with a small syringe containing a specific allergen to which the patient may be allergic. After a waiting period of about 15 minutes, the test is read. Positive reactions on the skin testing are typically a red, itchy area with a raised center that may look like a mosquito bite. Skin testing on the arm is compared with negative (saline) and positive (histamine) controls to help gauge the intensity of the reaction.

What is the Treatment for Venom Allergy?

Immunotherapy is a series of allergy shots given to reduce your sensitivity to allergens that cause an allergic reaction. Small doses of allergens are injected under the skin. Over time, allergy shots can reduce the severity of your reaction to allergens. To treat allergies to insect stings, very small amounts of the venom of the insect or insects are used. The treatment also is sometimes called venom immunotherapy (VIT).
Immunotherapy is available to treat allergies to stings from:

  • Honeybees.
  • Yellow jackets.
  • Hornets.
  • Paper wasps.
  • Fire ants.

A solution of dilute saline containing a very small amount of the insect venom is injected under the skin. At first, you get one or more shots about once a week. The amount of allergen injected is slightly increased each time, unless you have a reaction to the shot.
After about 4 to 6 months of weekly shots, you are usually getting an optimal amount of allergen in the shot—this is called the maintenance dose. After you reach maintenance level, you get the same dose in shots every 4 weeks for another 4 to 6 months.
After the first year of shots, you will have maintenance shots every 6 to 8 weeks over the next 3 to 5 years.1

Depending on your situation, your doctor may recommend rush immunotherapy. Several shots are given over a period of days to weeks. This type of treatment can provide faster protection in the short term. But you will still need to have regular shots over the long term.

Immunotherapy can prevent life-threatening reactions and also reduce anxiety associated with insect stings.

An allergic reaction that spreads far from the sting or that affects the entire body is called a systemic reaction. Systemic reactions are not common but can be life-threatening. Allergy shots are usually recommended if an adult or child has had a severe systemic reaction, especially anaphylaxis. Immunotherapy reduces the risk of another severe systemic reaction.


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