Insect allergy
The most common cause of insect allergies are the families of the Apidae (honey bees and bumblebees), vespidae (hornets, paper wasps) and formicidae (fire ants). The major allergens in such species are the phospholipase A2, hyaluronidase, melittin, antigen 5 and various alkaloids (in the case of the fire ant).
The vast majority of bites cause a simple allergic reaction, a local reaction where the above allergens cause a release of local histamine , causing swelling. In rarer cases, a full systemic anaphylaxis can occur.
Anaphylaxis is a form of IgE immediate hypersensitivity when mast cells and basophils are provoked to secrete mediators with potent vasoactive and smooth muscle contractile activities causing a systemic response. Sting allergies affect about 2 million Americans (a little over 1%), with approximately 50 deaths/year.
Reactions can also be anaphylactoid reactions, these are reactions that produce the same clinical picture with anaphylaxis but are not Ig mediated, instead occur through direct non immune-mediated release of mediators from mast cells and/or basophils or the result of direct complement activation.
There are three presentations consistent with anaphylaxis/anaphylactoid reactions
- Acute onset that includes the skin and involvement of the respiratory tract and/or decrease in BP
- Rapid onset of a reaction after exposure to a likely allergen that involves two organ systems
- Reduction of BP after exposure to a known antigen
In rare cases serum sickness, a delayed reaction after the sting, can occur, patients present with fever, myalgias, arthralgias, rash, adenopathy and headaches.
Systemic reactions must be managed supportively, ensuring the patency of the airway, with prophylactic intubation if needed. Treat with fluids to maintain BP and adrenaline (epinephrine) is the main drug of choice (administer IM).