Yellow hornets (aerial yellow jackets) are members of the Vespidae (wasp) family found in temperate regions of Europe, Asia and North and South America. Vespid stings are common and cause mild to severe, localized and systemic allergic reactions including anaphylaxis, which may be fatal. Antigens 5 are the most abundant and allergenic proteins in vespid venom, demonstrating cross-reactivity between wasps, hornets and yellow jackets and also with fire ant venom and possibly mosquito and horsefly bites. Serological patterns of cross-reactivity are diverse and not necessarily correlated with clinical symptoms. There is conflicting evidence for cross-reactivity with bee venom.

Worldwide distribution 

The exact incidence of Hymenoptera stings is unknown, although an estimated 56–94% of adults have been stung at least once during their lifetime. In a North American study of 3,236 Hymenoptera-allergic subjects, each person averaged 2.7 stings during their lifetime and 89% reported at least one systemic allergic reaction (4). The prevalence of severe allergic reactions to Hymenoptera venom is estimated at between 3% and 8.9% of adults (4, 7). Insect sting-related anaphylaxis accounts for over 30% of all anaphylaxis cases seen in emergency departments and almost 20% of all deaths from anaphylaxis (4). Sensitization to vespid venom is found in 10–30% of people with no history of allergic reaction to vespid stings (5).

Risk factors 

Large local reactions to Hymenoptera venom, defined as non-life-threatening pain, swelling, and erythema which may involve an entire limb, occur in 2.4% to 26.4% of the general population, but nearly 40% in people who are stung regularly, such as beekeepers (4). Other risk factors include a history of atopy, previous severe immunologic reactions, mast cell disorders, elevated serum tryptase and antihypertensive therapy with angiotensin-converting enzyme inhibitors (8)

Pediatric issues 

Severe allergic reactions to Hymenoptera venom are seen in up to 1% of children (4, 7).

Hymenoptera species play an important role in crop pollination and in reduction of insect pest populations (4).

Main 

The main route of exposure is a yellow hornet sting.

Allergic reactions to hornet or yellow jacket stings are common; these are IgE-mediated and may be immediate or delayed. Most sting reactions are localized and self-limiting. Some present as a large local reaction: an area of swelling extending around the sting site and sometimes involving an entire limb or side of the face. These can be treated with ice packs, elevation and oral antihistamines and/or corticosteroids (2, 4).

Hymenoptera stings are one of the most frequent causes of severe anaphylaxis in adults. Symptoms include flushing, urticaria and angioedema as well as more serious gastrointestinal, respiratory and cardiovascular symptoms and multi-organ failure. Epinephrine (adrenaline) is the emergency treatment of choice (1, 4).

Around 10% of adults who have a mild systemic reaction to a sting will have a more severe reaction when stung again. Conversely, approximately 45% of patients with a moderate or severe reaction to their first sting will have a less severe reaction to future stings (3).

Almost 8% of subjects presenting with Hymenoptera allergy have mast cell disorders such as cutaneous mastocytosis. Patients with mast cell disorders and/or elevated baseline serum tryptase are at risk for more severe allergic reactions to vespid stings. Life-threatening sting reactions may be the only clinical presentation of these disorders (4, 5).

Anti-hypertensive therapy with angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) may be associated with severe allergic reactions (including anaphylaxis) following Hymenoptera stings and/or immunotherapy for Hymenoptera venom allergies. These reactions are attributed to systemic accumulation of bradykinin (8).

Venom-specific IgE is most easily detected 1–4 weeks after the sting has occurred. A combination of serum IgE evaluation followed by intra-dermal skin prick testing is recommended for accurate diagnosis of sensitivity reactions; although the two tests show discordance, they are complementary (5, 9). There is no correlation between the severity of sting reactions and skin test reactivity to whole venom extracts (5).

Venom-allergic patients with concurrent mastocytosis are more likely to have negative specific IgE (sIgE) levels than venom-allergic patients without mastocytosis (5).

Recombinant allergenic proteins are preferable to native Hymenoptera venom when differentiating between bee and wasp venom sensitivity, because recombinant allergens do not contain cross-reactive carbohydrate epitopes (10).

Allergen immunotherapy

Dolichovespula arenaria is available as a single venom protein extract for venom immunotherapy (VIT). VIT is recommended where patients are IgE-sensitized to the culprit species and their systemic reaction is more severe than cutaneous involvement (3). VIT protects 75%–95% of patients from a systemic allergic reaction following a subsequent sting, compared to a 40%–60% risk of systemic reaction in untreated subjects. When systemic allergic reactions do occur following VIT, they are usually mild and not life-threatening. VIT should continue for a minimum of 3–5 years, although some patients require life-long therapy (4).

In children, VIT for systemic allergic reactions to Hymenoptera venom is safe and appears to be more effective in inducing long-term tolerance than in adults (4).

Prevention strategies 

Self-injectable epinephrine (adrenaline) should be considered for all patients with a history of a sensitivity reaction to vespid stings, particularly those with previous moderate to severe reactions or increased risk of exposure (4, 5).

Author: RubyDuke Communications

Reviewer: Dr. Christian  Fischer

Last reviewed:March 2022