AAIQ   The Association of Allergists and Immunologists of Québec

Allergy to venomous insects

It is important to distinguish between venomous insects that sting and inject venom, and other insects that bite and that can occasionally cause problems with their saliva. Those people that have large local reactions to fly bites are not necessarily more at risk for an allergy to stinging venomous insects. The risk of having an allergy to stinging venomous insects is around 1%.

Different venomous insects

In Québec, the most frequent are part of the order hymenoptera :

* Wasps:   Paper wasp, yellow jacket, White-faced hornet; Yellow-faced hornet
* Honey-bees
* Bumble-bees

Bees rarely sting unless provoked. They sting to defend their hive or their queen. When they sting, they lose their stinger and die. Bee stings mostly occur in bee keepers, or in people who walk outside without shoes, or who work with plants and flowers. Bumble bees also rarely sting unless provoked.

Wasps are in general a lot more aggressive and sometimes sting without reason. They are often more aggressive in the fall when the wasp population is larger, yet food is scarce. They go looking for food, often hanging out near garbage cans and picnics!

Different reactions

There are different possible reactions to stings by venomous insects:

Local reaction: most people develop a light swelling, with redness and pain at the site of injection. The application of ice is often sufficient to treat this reaction.

Marked local reaction: important swelling and redness at the site of the sting that may gradually develop over 12-24 hours following the sting. Sometimes this reaction involves an entire limb. The symptoms usually disappear within 5-10 days.

This type of reaction can usually be controlled with antihistamines and sometimes requires corticosteroids.

This type of reaction is generally not dangerous unless the sting is localized to areas in the respiratory tract (mouth, throat...).

The risk of developing an anaphylactic reaction when restung by the same insect is 5-10%.

Systemic reaction: involves one or several bodily systems. There are therefore symptoms observed at sites distant from the sting. This type of reaction may range from only generalized urticaria to a full anaphylactic reaction.

The risk of a systemic reaction from a future sting in adults with a prior episode of (only) urticaria is around 20%.

The risk of a systemic reaction from a future sting in children (16 years and less) with a prior episode of (only) urticaria is around 10%. Their risk for a more severe reaction is less than 1%.

The risk of a systemic reaction from a future sting in adults with a prior episode of anaphylaxis is from 40% to 70% and ranges from 30% to 40% in children who have had a similar episode.

Anaphylactic reactions must be treated the same way as all other types of anaphylactic reactions, which is to say with epinephrine, and then by calling 9-1-1 (see also: Anaphylaxis).

Toxic reaction: often resembles a systemic reaction, usually due to a large number of simultaneous stings, rather than an allergic reaction.

Treatment of systemic reactions

Patients having a systemic reaction should be referred to an allergist. Immunotherapy is a recognized treatment option for patients having had allergies to venomous insects. This treatment is 95%-100% effective in preventing systemic reactions due to future stings and is usually given over a 3-5 year period. Immunotherapy is indicated in all adults having systemic sting reactions, and in children 16 years or less having had an anaphylactic reaction. Allergy skin testing is usually performed when there is an indication for immunotherapy.

Patients allergic to venomous insects must always carry during the season their epinephrine auto-injector and wear a medical alert bracelet describing their allergy.

Some precautions for avoiding stings

* Always wear shoes outside.
* Wear a hat with insect protection, especially in areas conducive to insect stings.
* Wear long sleeves and pants.
* Use gloves when working in the garden.
* Conserve food in closed containers when eating outdoors. Enclose all garbage. Drink from containers that close between sips, and always check your food or beverage before taking a bite or a drink.
* Eliminate all hives/nests as soon as possible.
* Insect repellent doesn't necessarily deter venomous stinging insects.
* Avoid bright colored clothing and perfumes, which attract insects.

Regarding fly bites

There are cases of anaphylactic reactions to bites from black flies, and deer and horse flies, but they are rare. No study has yet clearly demonstrated the efficacy of immunotherapy for these types of allergies. Cases of anaphylactic reactions to mosquito bites are extremely rare.

Severely allergic patients must scrupulously avoid these insects, and always have an epinephrine auto-injector available in the seasons when they are present.

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Simon Hotte, MD FRCPC
(translation: Andrew Moore, MD FRCPC)