Overview

Hornet venom allergy (HVA) implicates the allergic reactions triggered by the hornet's stings, caused by the venom injected into the victim’s body. Hornets are a species of large, aggressive wasps, and their stings may provoke mild inflammation to severe allergic reactions (anaphylaxis). After being stung, HVA involves symptoms such as swelling, itching, difficulty breathing, hypotension, shock, etc. Hornet stings can happen to anyone belonging to any age, especially to people working as construction workers, entomologists, beekeepers, landscapers, or exterminators. Most people are stung unexpectedly when coming in contact with these reclusive territorial hornets, or when they are close to a disturbed nest.

Hornet and its venom

• Hornets belong to the class “Hymenoptera” and the family Vespidae of insects, which comprises nearly 150,000 different species of insects
• There are two types of hornets: first is the adult European hornet estimated to be 1-1.5 inches long with its head, thorax, first abdominal segment, and legs of reddish-brown colour and remaining abdomen of dark yellow with brownish bands and small spots; the second type is a baldfaced hornet (similar to the larger variant of yellow jackets) with white facial and thoracic markings
• These hornets carry therapeutic value in the United States
• Hornets create nests in hollow trees and wall voids
• The female hornets have modified ovipositors, i.e. female reproductive organs in their abdomen (stingers), which they use to inject venom as a means of defence, and to subdue the prey; thus, female hornets can only sting
• Hornets insert about 3g of venom in every sting and could sting multiple times, causing a cramping, erythematous bump on the sting site. The venom injected by stings ( bees, wasps, hornets,  and yellow jackets) causes hypersensitivity reactions and anaphylaxis, and that has resulted in multiple deaths in the United States
• The venom includes a fusion of tiny low-molecular-weight proteolytic enzymes (hyaluronidase, proteases, phospholipase, acid phosphatase), lipids, carbohydrates, and some high-molecular-weight allergic proteins. The local inflammatory reactions are due to low-molecular-weight elements, but the high-molecular-weight elements cause anaphylactic reactions
• When the hornets inject venom on the subject’s skin, mast cells are activated, producing histamines and basophils are activated, promoting dilation of blood vessels and inflammation (swelling, pain, redness, and rise in temperature on the site)
• Around 10% of Hymenoptera stings lead to local large reactions (LLRs), likely due to an immune response involving IgE antibodies. People with preformed antibodies to high molecular weight components of venom suffer from anaphylaxis

Symptoms 

• The hornet’s venom can lead to large localised reactions or systemic reactions in the person
• Most sting reactions subside themselves with some time
• Localised allergic reaction presents as a painful and pruritic raised lesion around 2cm in width based on the body’s sensitisation. It is covered with swelling of a width of approximately 10cm and lasts for 24 hours. Stinging on the head and neck areas is critical, and the bumps are shorter as compared to those present on the extremities
• Red round spots on the sting site are a typical feature of an instant allergic reaction
• Noxious effects like hemolysis, rhabdomyolysis, and possible kidney damage
• Systemic reactions may significantly differ due to the distinctive components present in the venom and their corresponding reaction
• The reaction after a sting can be both allergic or non-allergic and is divided into four stages:
  • Itching, erythema, urticaria(skin hives), rhinitis, Angioedema, nausea, acute pain, small to larger swelling with redness, inflammation, and hotness on the sting site
  • Asthma, angioedema, abdominal pain, redness, and swelling on the sting site up to 5-10 days
  • Difficulty breathing or respiratory distress involving Laryngeal oedema/asthma, remarkable hypotension, collapse, loss of consciousness, breathlessness, laryngeal stridor, difficulty in swallowing and speaking, abnormal voice, and fear of death
  • Downfall in blood pressure, collapse, urinary and faecal incontinence, bluish skin discolouration, and loss of consciousness. It may also involve systemic allergic reaction/ anaphylaxis approximately after 10 minutes of stinging. Symptoms such as facial, throat, lip, and tongue swellings, malaise, low blood pressure, fast pulse, dizziness, nausea, vomiting, and light-headedness are present

Diagnosis

It involves some skin and blood tests that detect the allergen-specific IgE antibodies. Skin Prick tests and intradermal tests are done at a minimum of two weeks after the sting. Both medical history and clinical assessment are essential for accurate diagnosis.

• Skin Prick Testing (SPT): To recognise the allergens causing the allergy. The skin is pierced or scratched with purified allergen to check for instant allergies. The amount of redness, swelling, and size of the lesion are determined
• RAST inhibition test: It is a radioimmunoassay for identifying specific IgE or siege antibodies in reaction to allergens. Also, it distinguishes genuine dual sensitivity and cross-reactivity
• IMMULITE test: It determines the particularity of insect venom allergens and their sensitivity. Moreover, it characterises the exact cross-reactivity in allergic patients to insect venom
• Recombinant allergens are used for skin testing and serological diagnosis
• Basophil Activation test (BAT): is a flow cytometry-based assay that helps recognise primary sensitising antigens in Hymenoptera venom allergy. It also aids in mastocytosis patients
• Component-resolved diagnosis: It makes use of purified allergens to recognise specific IgE reactivity in defiance of the individual allergic molecules
• Differential diagnosis: Other insect bites, Folliculitis, Abscess, Cellulitis, Anaphylaxis to different allergens

Risk factors and triggers

• Beekeepers, construction workers, entomologists, landscapers, or exterminators could often be stung, thus they and their families suffer from venom allergy
• IgE sensitisation to venom may lead to systemic reactions
• Systemic reactions in people are suspected after a prior local large reaction
• Mostly, kids are at risk of skin-related systemic reactions, but adults may suffer from cardiac and respiratory complications. 
• Hornets (Wasps) are more functional in summer and autumn
• Rare but lethal situations may arise in people with increased mastocytosis or baseline serum tryptase and with precedent heart and respiratory disorders
• Elderly people above the age of 40 years, asthmatic patients, or a history of any allergies due to insect stings

Management and treatment

• Allergists should be consulted as per the severity of the symptoms
• Mild allergies and local reactions: ice packs, NSAIDs/Acetaminophen, H1/H2 blockers (supportive care)
• The stinger is detached with the help of a credit card, not exceeding more than the first few minutes post-sting; squeezing/tweezing may further cause venom exposure, and thus is contraindicated
• Massive local reactions- for reducing the inflammation and relieving symptoms, Supportive care, and Glucocorticoids (prednisone 40 to 60 mg per day for 3-5 days)
• For anaphylaxis/systemic reactions:
  • ABCs: Evaluate airway, Breathing, and Circulation first. Early intubation because the airway may be compromised in a very short duration(seconds to minutes)
  • Epinephrine, Corticosteroids, H1 and H2 antagonists, and IV fluids should be administered instantly. 0.3 to 0.5mg Epinephrine to be given via IM route on the anterolateral thigh with persistent administration every 5 to 15 minutes
  • Corticosteroids (prednisone, dexamethasone) aid in reducing inflammation
  • H1 and H2 antagonists obstruct the histamine's course of action, relieving itching, erythema, and urticaria
• People with experience of previous anaphylaxis reactions should always keep an auto-injecting epinephrine pen.

Venom-specific immunotherapy

It comprises subcutaneous injections of increasing doses of purified wasp venom extract. It is proficient in avoiding allergic responses to insect stings. Individuals presenting with deadly anaphylactic reactions are given omalizumab and VIT therapy. Molecular approaches ( transcriptomic, proteomic, peptidomic, glycomic, and venomic) are required to develop effective therapeutics for envenomation. Data on peptide toxins can be used to create new diagnostic and therapeutic measures. Anti-venom serum production against important toxins/allergens can be used in immunotherapy for envenomation treatment. Allergen immunotherapy, involving a series of allergen extract injections, is applied for severe or unresponsive allergies.

Complications

• Poor quality of life due to social boundaries; Stress and anxiety
• Secondary bacterial infections: Lymphangitis, Cellulitis
• Skin blisters
• Recurring reactions extending from weeks to months.
• Vasculitis, Neurological complications, Serum sickness.

FAQs

How common is hornet venom allergy?

The wasp's stings are sporadic, probably once every 10-15 years; People except if linked to specific occupations like those close to nature or insect-related fields, are at risk.

How can I prevent hornet venom allergy?

• Healthcare professionals' guidance for patients regarding the avoidance of insect bites
• People with having history of serious anaphylaxis should have regular consultations and immunotherapy with allergists
• Wear protective attire, and non-bright clothes and refrain from perfume when close to insect hives or nests
• Avoiding loud music around these insects that could irritate them
• Staying away from wasp nests; If one is in close proximity, one should get rid of them with the help of professionals
• Individuals with previous allergies should always have epinephrine injections with them
• Never disturb their nests

What can I expect if I get a hornet venom allergy?

• Vomiting, nausea, or diarrhoea
• Abdominal pain
• Unconsciousness or cardiac arrest
• After a sting, in literally minutes, anaphylaxis can occur, causing difficulty breathing and low blood pressure; it may result in shock

When should I see a doctor?

• When the sting lesion does not subside by itself within a few days
•  In case of extreme anaphylactic reactions, difficulty in breathing, speaking, and swallowing
•  Urticaria, loss of consciousness, land ow blood pressure

Summary

Hornets are solitary, aggressive insects. Their sting venom produces a hornet venom allergy, which refers to a severe allergic reaction. When an individual is stung, mild to moderate symptoms like localised swelling, itching, redness, inflammation, etc can occur depending on person to person. But in cases of severe anaphylactic reactions, symptoms such as dysphagia, dyspnea, breathlessness, hypotension, loss of consciousness, low blood pressure, and shock could lead to life-threatening situations. These require immediate medical help. People with a history of HVA should take precautions, like always keeping epinephrine injections with them. HVA. Effective diagnosis and management could save lives. Venom immunotherapy reestablishes normal immunity against venom allergens.