Etiology

• Female bees and their cousins, the bumblebees, wasps, hornets and ants, do not usually sting unless stepped on, touched, or molested.
• The poison gland system of the bee consists of a small alkaline gland and a larger acid gland. In the bee the venom is produced by these two glands, which are associated with the ovipositor (egg-laying organ) of the female. The stinger is made up of two lancets with sharp barbs pointing backward, similar to a harpoon. This distinction is important because it means that the sting of a bee will usually remain implanted in the skin of the individual that has been stung. In doing so, it will tear away from the bee's abdomen, leading to the death of the bee. The stinger left behind by the bee can continue to inject venom into the tissues.
• Wasps and hornets, by contrast, have smooth stingers and are therefore able to retain their stingers.
• The Imported Fire Ant can be very aggressive if their nest is disturbed.
• Massive venom attacks occur in the Americas from so called Africanized or killer bees (Apis mellifera scutellata).  These are descendants of African bees that escaped from a research facility in Brazil in 1957 and hybridized with local bees.  The venom of Africanized bees is similar to that of domesticated honeybee, but the bees are more aggressive and the risk of multiple stings is far greater.  They are stimulated to an aggressive state quicker than other bees and will pursue for a long distance.

Predisposing factors

General

• Contact with bees, wasps and other stinging insects.

Specific

• Insects are attracted to flower fragrances, bright colors against dark backgrounds as well as sugary foods.
• Bees and wasps tend to frequent clover fields, orchards, picnic sites and dustbins.
• Certain insects, including the Imported Fire Ant, are aggressive if their nest is disturbed.

Pathophysiology

• Bee venom is a very complicated substance with several active biochemical components.
• At least eight active components plus several biological inactive components have been identified. The substances showing activity are histamine, melittin (a protein), a hyaluronidase, and phospholipase A.
• Histamine is not thought to be a pharmacological factor in bee venom. Histamine can, however, be released in allergic individuals in response to the sting.
• The protein, melittin, is thought to be responsible for the general local toxicity of the venom and, at high concentrations, can cause hemolysis of red blood cells.
• Bee venom contains at least two enzymes, including a hyaluronidase and phospholipase A. Hyaluronidase facilitates venom infiltration through the tissues. Phospholipase A causes inactivation of thrombokinase, inhibits oxidative phosphorylation, and attacks enzymes involved with metabolic dehydrogenation. The pain experienced after being stung may well be the result of these last three actions.
• Wasp venom also contains the enzymes hyaluronidase and phospholipase A.
• Sensitization to insect venom can occur after a single sting.
• The most allergenic component of wasp venom is a protein called Antigen 5 (or Ves g V). The most allergenic component of bee venom is the enzyme phospholipase. The hyaluronidase enzymes present in both bee and wasp venom may result in cross reaction allergy but the incidence of this in dogs is uncertain.
• The bulk of Imported Fire Ant venom consists of piperidine alkaloids. These are present in a non-protein, non-polar alkaline phase. The alkaloids are cytotoxic and are responsible for the severe inflammatory response.
• Formic acid, produced by ants, has a pH of 2-3 and is therefore markedly acidic.

Timecourse

• Non allergic reactions may develop over a period of up to several hours and resolve over the following few days.
• Allergic reactions in sensitized individuals may develop within 10 min of a sting.