Insect Sting Allergy
Insect sting allergy can be life-threatening. Insects that sting rather than those that bite are almost always responsible for these reactions because through a sting, venom is usually injected into the person who then experiences the reaction. These insects are members of the order of Hymenoptera. Stinging insects of concern are found in three families:
- Vespids (Vespidae): Including yellow jackets, hornets, and wasps.
- Bees (Apidae): Honeybees are the most frequent offenders with bumblebees causing significantly fewer reactions.
- Ants (Formicidae): Including fire ants and Harvester ants. Although painful, Harvester ant stings are a less common cause of anaphylaxis. Imported fire ant stings are known to cause systemic (whole body) allergic reactions in their habitat in the southeastern U.S. and along the Gulf Coast. They characteristically bite to attach themselves to their victim and then sting multiple times in a semicircular pattern with a sterile pustule forming after several hours at each sting site.
There have been rare case reports of allergic reactions to bites from deer flies, kissing bugs, bed bugs and mosquitoes, but such reactions are extremely rare. More common are large local reactions to these bites that, although unpleasant, are not life threatening.
Symptoms and Diagnosis
The first step in making the diagnosis of any of allergic reaction consists of taking a careful history and attempting to identify the responsible allergen (in this case an insect). Nesting and behavior patterns and a description of the insect and the sting may aid identification. For example, honeybees, because their stinger is barbed, usually lose their stinging apparatus, leaving it stuck in the victim at the site of the sting. Thus, stinging is a fatal event for a honeybee. However, this alone is not diagnostic of a honeybee sting because vespids can also lose their stingers about 8 percent of the time. Yellow jackets can be aggressive and are frequently encountered during outdoor events involving food and canned beverages.
Unfortunately, accurate identification of the insect based on the history alone is not always possible. People with histories suggestive of significant sting reaction should be referred to an allergist. The usual procedure is to skin test with the five commercially available venoms: honey bee, paper wasp, yellow jacket, yellow hornet and white-faced hornet. If appropriate whole-body extracts for imported fire ant and other biting insects are also available for testing. If the history is very suggestive of a generalized reaction and skin tests are negative, they should be repeated and/or blood tests for IgE (allergy-type antibodies) to specific venoms should be obtained.
Insect sting reactions can be classified as immediate or delayed based upon their timing. Reactions can also be toxic, or allergic. A toxic reaction is due to compounds in the venom itself acting on cells and tissues of the body. A true allergic response is a result of the immune system making specific allergic antibodies to components of the insect venom, leading - with exposure - to the generation and release of a variety of chemicals such as histamine that act on surrounding tissue to cause the symptoms associated with allergic reaction.
Immediate reactions are those reactions occurring within minutes to hours of a sting and can be further divided into local, large local, anaphylactic and toxic reactions. Immediate local reactions are often considered the "normal reaction." Signs and symptoms of immediate localized reactions are limited to the area of the sting site. Local reactions can occur in individuals who are not allergic to the insect.
Signs and symptoms of a local reaction may consist of:
- mild itching that may last for several hours
Large Local Reactions
Large local reactions are characterized by redness and swelling that begins within minutes to hours of a sting and extends from the sting site over a large surrounding area. These reactions often peak within 48 to 72 hours and last up to 10 days. They may be accompanied by fatigue, low-grade fever, mild nausea, and discomfort and are often misdiagnosed as cellulitis.
Anaphylaxis is the most severe insect sting reaction. This rapid reaction, usually involving multiple organ systems at the same time, most often begins within minutes of the sting although it can occasionally begin an hour or so later. If an anaphylactic reaction is suspected, FIRST give injectable epinephrine followed by an antihistamine (if available) and call 911 immediately. NEVER just rely on an antihistamine by itself as this class of medication does not prevent or treat anaphylaxis. Signs and symptoms may consist of:
- flushing, itching
- sneezing, runny nose
- nausea, vomiting, diarrhea
- abdominal cramping
- heart irregularities
- swelling in the throat, difficulty swallowing
- difficulty trouble breathing, cough, wheezing
- drop in blood pressure (hypotension), dizziness
- loss of consciousness
In the event of a sting from a poisonous spider or insect; or multiple, simultaneous stings from otherwise non-poisonous insects (as might be the case when a nest is disturbed, or when Africanized honeybees are involved); a toxic reaction may result. Toxic reactions are not caused by an allergic response, but rather by the effects of venom that acts as a poison. Local and toxic reactions can be seen in individuals who are not insect sting allergic, although some patients who experience toxic reactions can become allergic to insect venom later. Symptoms of a toxic reaction vary depending on the toxicity of the venom of the insect or spider, the amount of venom injected, and the individual's tolerance for that particular venom. Signs and symptoms may consist of:
- rapid swelling at the site of the sting
- muscle spasms
- fainting (syncope)
Usually, symptoms lessen or go away within 48 hours. Hives and shortness of breath may occur in an allergic reaction, but not in a toxic reaction. Though it is possible to have both a toxic reaction and an allergic reaction at the same time, this rarely occurs. A toxic reaction can be life-threatening and may lead to heart problems, shock and death.
If a toxic reaction is suspected, call 911, or seek professional medical attention immediately.
Reactions occurring more than four hours after a sting are classified as delayed reactions. There have been isolated reports of serum sickness-like syndromes occurring about a week after a sting. Other unusual reactions that have been reported in association with insect stings include Guillain-Barre syndrome, glomerulonephritis, myocarditis, vasculitis and encephalitis. Signs and symptoms may include:
- general discomfort
- joint pain
- pain or partial paralysis of extremities (hands, arms, feet, and legs)
- kidney/flank pain
- chest pain (angina)
- headache and dizziness
Management of Sting Reactions
- Treatment of local reactions in people without a history of insect sting allergy includes: acetaminophen or ibuprofen for pain and ice to reduce swelling.
- For those with a history of large local reactions, taking an oral antihistamine (preferably non-sedating) and, in some cases, taking a single dose of oral steroids soon after the sting is recommended.
- Venom allergy shots (immunotherapy) are highly effective in preventing subsequent allergic sting reactions. After reaching maintenance doses of immunotherapy, 95 percent of venom-treated patients can tolerate single stings, and any sting reactions that occur are milder. Adult patients who have a positive history and positive venom skin test or blood tests generally are considered candidates for specific-venom immunotherapy. Children with skin symptoms alone have only a 10 percent risk of systemic reactions and aren't considered candidates for skin testing or immunotherapy. Nonetheless, children with more severe or life-threatening reactions may be candidates for venom immunotherapy.
- Wear a medical alert bracelet or necklace stating that you (or your child) are allergic to insect stings.
- Be familiar with the potential symptoms of allergic reactions to insect stings. Your family should also be familiar with this information. Ask your healthcare provider to give you a written action plan. If an epinephrine injection device is prescribed, learn when and how to use it. Make sure that all caretakers understand the action plan and how to give the epinephrine and any other medication prescribed for the treatment of reactions.
- Carry an emergency pack at all times. The emergency pack should contain each of the medications needed to treat a sting reaction, such as an epinephrine injection device and an antihistamine in the form of syrup or chewable tablet. If you or your child has asthma, a rescue inhaler should also be kept in the emergency pack. An action plan card indicating the actions to take and the importance of calling 911 or going to the closest medical facility once the medication is given is also helpful. Follow the manufacturer’s instructions regarding storage of your epinephrine injection device and replacement of the device before the expiration date.