Bites and Stings, Insect

• Lynn A. Bowlby, M.D.

 Basic Information

Definition

Most stinging insects belong to the Hymenoptera order and include honey bees, hornets, bumblebees, sweat bees, wasps (including yellow jackets), harvester ants, fire ants, and the Africanized honey bee (“killer bee”). Thousands of species can sting. Wasps cause 70% of all reactions to stings. Spiders, which are arachnids, not insects, are another cause of bites (Fig. 1) (see “Bites and Stings, Arachnids”). The venom of the Hymenoptera order contains vasoactive and proinflammatory mediators that can cause local reactions. A small number of those stung can develop a systemic hypersensitivity reaction. The usual local effect of a sting is intense pain, immediate erythema, edema, and pruritus from the injecting venom. Allergic reactions can be either local or generalized. Generalized reactions can lead to anaphylactic shock. This is a rapid-onset event and can cause death. The majority of reactions occur within the first 6 hr after the sting or bite, but a delayed reaction may occur up to 24 hr after the sting. Delayed reactions are rare and include serum sickness (fever, malaise, urticaria, and arthralgias).

Synonyms

1. Venom allergy

ICD-10CM CODES
T63.444	Toxic effect of venom of bees, undetermined, initial encounter
T63.464	Toxic effect of venom of wasps, undetermined, initial encounter
T63.424	Toxic effect of venom of ants, undetermined, initial encounter

Epidemiology & Demographics

Prevalence (Of Bee Stings and Insect Bites)

1. Unknown prevalence, very underreported.

2. Account for 2.3% of ED visits. 5% to 7.5% of the population is hypersensitive, with large local or systemic reactions to the venom of one or more stinging insects.

3. Insect bites are the most common cause of anaphylaxis reactions and account for 20% of all anaphylaxis-related deaths.

4. Most anaphylactic reactions occur during summer months in those most likely to be exposed, including children, males, outdoor workers. There are no tests to predict reaction accurately; the reaction to a prior sting is still the best predictor. Anaphylaxis can occur after a number of uneventful stings.

5. Approximately half of fatal reactions occur without prior allergic response.

6. Bites by fire ants are less likely to cause systemic disease.

7. Spider bites are rare; only a few of the thousands of spider species cause a reaction in humans. Observation and collection of the spider inflicting the bite is necessary (see Bites and Stings, Arachnids).

Incidence (In U.S.)

Forty to 100 people die each year from insect sting anaphylaxis; anaphylaxis occurs most often within 10 to 30 min of a sting. Delayed reactions are rare, occurring only in <0.3% of stings.

Physical Findings & Clinical Presentation

Stings:

1. Local reactions:

   1. Cutaneous: the skin is the most common site of a local allergic reaction. Manifestations include flushing, urticaria, pruritus, and angioedema. Local reactions may last several days.

2. Systemic reactions:

   1. Local swelling greater than 10 cm is associated with increased risk of a systemic reaction with repeat exposure.

   2. Respiratory: This is the leading cause of anaphylactic death. Anaphylaxis as defined by consensus of the NIH 2006 as a severe life-threatening hypersensitivity reaction. Symptoms of upper and lower airway obstruction including hoarseness, choking, throat tightness or tingling that may progress to stridor, laryngeal edema, laryngospasm, and bronchoconstriction.

   3. Cardiovascular: Cardiac manifestations are the second leading cause of death from anaphylaxis; the most common reaction is hypotension that can progress to profound hypovolemic shock. Tachycardia and arrhythmia may occur. Myocardial infarction is rare.

   4. General symptoms: abdominal pain, nausea, vomiting, lightheadedness, and diarrhea.

3. Fire ant bites:

   1. Initial wheal and flare response.

   2. Subsequent development of circularly arrayed blisters within 24 hr (Fig. E2).

      

   3. Blisters may develop the appearance of pustules, but they are not infected.

4. Flea bites:

   1. Classic linear configuration (Fig. 3)

      

   2. Multiple excoriated, clustered red papules (Fig. 4)

      

Etiology

Stings:

1. Most systemic reactions to insect stings are classic immunoglobulin E (IgE)–mediated reactions. Anaphylaxis can be the presenting sign of indolent mastocytosis.

2. Reactions occur in previously sensitized patients who have produced high titers of IgE antibody to insect venom antigens.

3. Sensitization to wasp venom can occur after a single sting but is more common after a few stings.

4. Sensitization to bee venom occurs mainly in people who have been stung frequently by bees.

Bites:

1. Fire ant venom contains proteins toxic to the skin.

Diagnosis

Differential Diagnosis

1. Stings: cellulitis, bites, rash

2. Bites: stings, cellulitis

Workup

The history is essential for accurate diagnosis including timing of sting or bite and type of insect (bee, wasp, spider, or ant) if known.

Laboratory Tests (For Hypersensitivity Reaction)

1. Skin test: either skin prick test or intradermal method with fire ant or hymenoptera venom.

2. Venom skin tests and occasionally radioallergosorbent tests (RAST) to provide additional information, only for those with history of a systemic reaction.

3. Venom-specific IgE tests

4. Basophil activation tests and mast cell mediator testing are being developed to identify those with allergy and predict those who will have more severe reactions.

5. Measuring baseline serum tryptase can identify patients as high risk for anaphylaxis and those with mastocytosis.

Treatment

Acute General Rx

Sting:

1. Local Poison Control Center can be contacted.

2. Removal of the stinger most easily performed with a flat tool such as a credit card within 30 seconds of the sting, followed by cleansing and application of ice.

3. Venom may all be released within 20 seconds of bite or sting.

4. Avoid squeezing, which may push venom out of the venom sac and into the tissue.

5. Supportive care with oral antihistamines, nonsteroidal antiinflammatory medications/pain medications, topical corticosteroids for 5 to 7 days, and cold compresses for limited reactions.

6. Large local reactions (>10 cm) may benefit from oral steroids. Maximum of 50 mg/day of prednisone for 5 to 7 days. Oral second-generation antihistamine can treat and prevent this reaction.

7. Patients with previous reactions or multiple stings to the mouth or neck should be evaluated in an emergency department.

8. Unusual reactions to multiple stings include cerebrovascular accident or acute kidney injury due to many causes, including hypotension or direct toxicity from venom.

9. Systemic reactions: Treat quickly with intramuscular epinephrine (no contraindication for use). Increased risk of death if epinephrine delayed. The patient should be supine with 0.30 mg IM in anterior/lateral thigh. Patient should be observed for 4 to 8 hours.

10. H1- and H2-blockers, oxygen, IV glucocorticoids, beta-agonists, pressors, and IV fluids may also be beneficial for anaphylaxis. No data that glucocorticoids improve clinical outcomes.

11. Patients should be given 2 units of self-injectable epinephrine pens for home use and referral to allergy indicated after a systemic reaction. Patients should be transported to ED if epinephrine is used, due to 20% risk of recurrence of symptoms.

Bite:

1. Supportive care—wash with soap and water

2. Application of ice or cooling. Calamine lotion may be helpful.

3. Surveillance for secondary infection

Disposition

Sting:

1. Prognosis for a limited reaction is excellent.

2. Subsequent anaphylaxis may occur in up to 65% of patients stung again with history of prior systemic reaction. Large local reaction does not predict a systemic reaction.

3. There is no evidence that the next sting will necessarily cause a more severe reaction. Variable outcome is due to the patient’s age, comorbidities, time elapsed since prior exposure, dose of venom injected, and site of sting.

4. Watch for secondary cellulitis.

5. Patients who have a history of a severe systemic reaction should:

   1. Be educated to avoid stinging insects

   2. Carry 2 syringes preloaded with epinephrine for self-administration

   3. Undergo testing for serum levels of venom-specific IgE

   4. Be referred to allergist for venom immunotherapy (VIT), which reduces chance of serious allergic reaction from 60% to <5%. VIT is typically needed for 3 to 5 yr.

   5. Carry medical identification for stinging insect hypersensitivity

   6. Have a baseline tryptase level checked if an anaphylactic reaction to a sting has been experienced in the past to evaluate the possibility of an underlying mast cell disorder. Patients with levels >20 ng/ml need further evaluation. VIT may benefit those with mastocytosis and wasp venom allergy.

Bite:

1. Prognosis for fire ant bite is excellent.

2. Large lesions from brown recluse spider bites may take months to heal.

3. Watch for secondary cellulitis.

Referral

1. Consider referral to an allergist for venom immunotherapy (VIT). All patients with severe systemic reactions should be referred for testing and, if positive, should receive VIT for 5 years.

2. Risk of subsequent anaphylaxis with immunotherapy falls to <5%.

3. VIT for 5 yr induces long-term protection in most patients.

Pearls & Considerations

Hypersensitivity to stings is common. Reactions range from local nonallergic reaction to venom to life-threatening systemic reaction with anaphylaxis. This could indicate underlying mast cell disorder; tryptase level is indicated. Venom-specific immunotherapy is highly effective in decreasing subsequent anaphylaxis. Although venom immunotherapy is currently indicated only for systemic reactions, investigation is under way to assess efficacy for prevention of large local reactions, which can result in significant morbidity.

Suggested Readings

• Anaphylaxis and insect stings and bites. JAMA. 318 (1):86–87 2017

• D. Antolin-Amerigo, et al.: Venom immunotherapy: an updated review. Curr Allergy Asthma Rep. 14 (7):449 2014 24934908

• T.B. Casale: Wesley Burks A: Hymenoptera-sting hypersensitivity. N Engl J Med. 370:1432–1439 2014 24716682

• T.M. Freeman: Hypersensitivity to hymenoptera stings. N Engl J Med. 351 (19):2004 1978

• D. Golden, et al.: Stinging insect hypersensitivity: a practice parameter update 2016. Ann Allergy Asthma Immunol. 118:28–54 2017 28007086

• N.G. Kounis, et al.: Foods, drugs and environmental factors: novel Kounis syndrome offenders. J Intern Med. 54 (13):1577–1582 2015

• H. Lee, et al. Insect allergy. Primary Care: Clinical in Office Practice. 43 (3):417–431 2016

• K. Lee-Sarwar, et al.: A stinging sensation. N Engl J Med. 372:e35 2015 26107069

• G.B.D. Silva Jr., et al.: Acute kidney Injury complicating bee stings: a review. Rev Inst Med Trop Sao Paulo. 59:e25 2017 28591253

• Venom immunotherapy for preventing allergic reactions to insect stings. Cochrane Database Systemic Review. 17 October 2012

• M. Worm, et al.: Triggers and treatment of anaphylaxis: an analysis of 4,000 cases from Germany, Austria, and Switzerland. Dtsch Arztebl Int. 111 (21):367–375 2014 24939374

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Bites and Stings (Patient Information)

Bites and Stings, Arachnids (Related Key Topic)