![]() ![]() Anaphylactoid reactions resemble anaphylaxis but are independent of IgE and, although compounds have been identified that act directly on cell membranes of mast cells, the exact mechanism for these reactions remains unclear ( 12). Anaphylaxis, a Type I (immediate) hypersensitivity mediated by IgE, is the most serious complication in dogs. Reactions to insect envenomation fall into 5 main categories: local pain and swelling, larger regional reaction, anaphylactic reaction, serum sickness (delayed-type hypersensitivity) occurring 3 d to 2 wk after envenomation, and a rare delayed toxic reaction in humans seen within 24 h after severe envenomation characterized by hemolysis, coagulopathy, hepatopathy, thrombocytopenia, and disseminated intravascular coagulation (DIC) ( 1, 11). ![]() Hyaluronidase causes breakdown of connective tissue and promotes further uptake and spread of venom ( 6). Peptide 401 causes mast cells to release histamine and vasoactive amines causing vasodilation ( 1). Melittin has also been associated with acute myocardial ischemia, producing arrhythmias ( 6, 10). This in turn releases myoglobin and hemoglobin, which have been linked to acute tubular necrosis and acute kidney injury (AKI) in humans and other species, including dogs ( 7– 9). Melittin, acting synergistically with phospholipase A 2, disrupts cell membranes of certain mammals and causes lysis of erythrocytes, leukocytes, platelets, myocytes, and vascular endothelium ( 6). The main components of bee venom are: melittin, peptide 401 (mast cell degranulating peptide), phospholipase A 2, hyaluronidase, histamine, dopamine, acid phosphatase, apamine, and norepinephrine ( 5), with melittin being the main component of venom both by amount and lethality. The venom sac continues to contract outside the bee’s body and 100% of the venom is delivered within 60 s ( 4). Honeybees are only able to sting once, as their barbed stinger catches in the victim’s skin, pulling the stinging apparatus from the bee’s body causing the bee to die. The venom in the sting can cause pathology ranging from local benign lesions to severe life-threatening systemic reactions. Although honeybees are comparably more docile than most of these venomous hymenopterans, they are very protective of their hives and they will attack humans or animals that pose a threat to their habitat. The 3 groups of Hymenoptera most frequently responsible for physical symptoms relating to allergic reactions seen in veterinary hospitals are: Apidae (bees), Vespidae (hornets, wasps, and yellow jackets), and Formicidae (fire ants) ( 3). ![]() Severe systemic allergic reactions in dogs living in North America most commonly occur because of an insect bite or sting, and the most clinically important encounters originate from insects belonging to the order Hymenoptera ( 1, 2). ![]()
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