Hymenoptera
The order Hymenoptera of the phylum Arthropoda can be divided into three subgroups that are medically relevant: (1) Apidae (Apids), which include the honeybee and bumblebee; (2) Vespidae, (Vespids) which include yellow jackets, hornets and wasps; and (3) Formicidae (ants).6
Bees and Wasps
The main allergens in Apid venom are phospholipase A2, hyaluronidase, and melittin. Melittin, the main component, is a membrane active polypeptide that causes degranulation of basophils and mast cells. The allergens in Vespid venom are phospholipase, hyaluronidase, and antigen 5. As all Hymenoptera share some of these components, cross-sensitization may occur and individuals may be allergic to more than one species.7
Occasionally after multiple stings, patients present with symptoms of a systemic toxic reaction. This is often seen in an Africanized bee attack. These so-called “killer bees” are hybrids of African bees that escaped from laboratories in Brazil in the 1950s and spread northward; they are found in most of the warmer US states. Their venom is not more toxic than that of any other bee, but Africanized honeybees are more aggressive and respond to a perceived threat in far greater numbers. The reaction that results from multiple stings is systemic and may resemble anaphylaxis. Common symptoms include nausea, vomiting, and diarrhea, as well as lightheadedness and syncope. Interestingly, urticaria and bronchospasm are not universally present, even though respiratory failure and cardiac arrest may occur. Other symptoms include renal failure with acute tubular necrosis, myoglobinuria or hemoglobinuria, hepatic failure, and disseminated intravascular coagulation (DIC).10,11 In addition, there have been reports of unusual reactions such as vasculitis, nephrosis, neuritis, encephalitis, and serum sickness. Late-appearing symptoms usually start several days to weeks after a sting and tend last for a prolonged period of time. Serum sickness tends to appear 5 to 14 days after exposure and consists of fever, malaise, headache, urticaria, lymphadenopathy, and polyarthritis.12 Of note, patients who have venom-induced serum sickness may be at risk for anaphylaxis after subsequent stings and may therefore be suitable candidates for venom immunotherapy.13
Anaphylaxis
The definition of anaphylaxis is not universally agreed upon. The American Academy of Allergy, Asthma and Immunology defines anaphylaxis as a serious allergic response that often involves swelling, hives, hypotension and, in severe cases, shock. A major difference between anaphylaxis and other allergic reactions is that anaphylaxis typically involves more than one body system.14 The clinical features of anaphylaxis from insect stings are the same as those from other causes, typically generalized urticaria, facial flushing, and angioedema. Abdominal cramping, nausea, vomiting, and diarrhea are also seen. Life-threatening symptoms include stridor, circulatory collapse with shock, and bronchospasm. Symptoms usually begin 10 to 20 minutes after a sting, and almost all will develop within 6 hours. Interestingly, symptoms may recur 8 to 12 hours after the initial reaction.15-18