Insect Venom Allergy - 2018 WSAAI update

This is a Twitter summary from the 2018 WSAAI meeting. This summary was compiled from the tweets posted by @MatthewBowdish, an allergist/immunologist, who attended the 2018 Western Society of Allergy, Asthma and Immunology (WSAAI) meeting. The tweets were labeled #WSAAI. The text was edited and modified by me.

Cem Akin on "Venom Hypersensitivity".

56-94% of US population reported at least one insect sting; prevalence of large local rxns 2-26%; prevalence of systemic rxns 0.2-0.8% of kids and 0.5-3% of adults.

Risk factors for systemic reactions to insect stings: age older than 45, male, concurrent cardiovascular disease, beta-blocker & ACEI use, atopic background, previous systemic rxn, multiple stings, recent sting, serum tryptase higher than 5ng/mL.

Insect stings are the 3rd most common cause of anaphylaxis
in US emergency departments; 10% of all pts presenting w/anaphylaxis, 20% of all fatal anaphylaxis in US, equals ~40 deaths per year in the US (may be under-reported).

Hymenoptera Taxonomy:

Honeybees: herbivorous, hairy bodies, non-aggressive, evisceration upon stinging, usually accidental sting, nests are above ground and in trees.

Yellow jackets are carnivorous, scavengers, highly aggressive, stings more frequently in autumn, nests are in the ground and in cracks in buildings.

Yellow hornets (aka aerial yellow jacket, so similar behavior) are aggressive esp with vibration, nests are in trees and shrubs.

White-face hornet have black and white color, three white stripes at end of body, omnivorous, aggressive and can squirt venom from stinger into the eyes of nest intruders causing temporary blindness.

Paper wasps have nests in open combs located in eaves of the house, not as aggressive, feed on other insects and have dangling legs.

Fire ants bite to get hold, sting from abdomen, will sting repeatedly nearby and live in colonies nested in the soil that can be 1-2 ft in diameter.

Hymenoptera stinging insects:

Fire ants are distributed in the southern sections of the US and leave sterile pustules that are clustered, develop 24 hours after sting and are due to alkaline pH - image from Akin:

Honeybee allergens:

Honey bee venom: major allergens (phospholipase A2 - Api m1); each sting ~50mcg of venom, small subset of patients monosensitized to minor antigens and may not respond to venom IT as well and have a higher relapse rate after d/c IT.

Vespid allergens:

Antigen 5 is major vespid allergenic protein; there is extensive cross-reactivity within subfamily Vespinae (yellow jackets & hornets), but not much with Polistinae (wasps).

Venom skin testing recommended 3-6 weeks after systemic event:

Skin testing is preferred, but now people often use blood test first plus serum tryptase, and then skin test to negative venoms from blood work.

You definitely want to consider basal serum tryptase in patients with anaphylaxis, especially with severe or hypotensive reactions and negative test results, to look for systemic mastocytosis.

Small subset of patient with convincing history are negative to both blood and skin testing (~1%). So, you can repeat testing 3-6 months later.

Fire ant skin testing is done with whole-body extract.

Avoidance counseling:

Large local reactions

Large local reaction peaks in size 24-48 hours, defined as more than 10cm diameter swelling, resolves over 3-10 days, treated with cold compresses, NSAIDs, oral antihistamines, oral pred 2-5 days, epipen?

5-10% of patients with large local reactions will progress to systemic symptoms on subsequent sting.

Venom IT may reduce large local reactions. May be useful in pts with high frequency of stings, extremely large locals, personal h/o CV disease and/or to alleviate patient’s anxiety.

Risk of systemic reactions:

Also, those above age 16 with cutaneous reactions are unlikely to go on to systemic reactions and venom IT not necessarily indicated (based on each patient's individual risks, however).

In systemic reactions, venom IT is indicated for reduction of future risk of anaphyalxis:

Summary of Venom IT indications:

2017 Parameter Update: " patients receiving IT, there is limited and conflicting evidence that these medications increase the risk of anaphylaxis."

H1 blockers reduce large local reactions and mild systemic rxns but not anaphylaxis; montelukast may improve large local reactions.

Risk of systemic reactions to venom IT:

-traditional protocol - less than 5%
-rush protocols 5-10%
- ultrarush protocol 0-28% (median 11%)

Duration of Venom IT:

Relapse rate after discontinuing VIT greater with: very severe rxn on previous stings, elevated basal serum tryptase, systemic rxn during VIT (injection or sting), less than 5 yrs maintenance VIT, honeybee anaphylaxis, frequent exposure.

Venom IT in systemic mastocytosis patients:

Image source: Bee, Wikipedia, GNU Free Documentation License.

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