Bites of arthropods

Bites of arthropodsStings and bites of arthropods are most often merely a nuisance. Some arthropods, however, can produce death by direct toxicity or by hypersensitivity reactions.

Bites of Bees & Wasps

When a bee stings, it becomes anchored by the two barbed lancets, so that withdrawal is impossible. In the struggle, a bee will usually avulse its stinging apparatus and die. After being stung by a bee, one should scrape the exuded poison sac with a sharp knife. Any attempt to pull the poison apparatus out will simply cause more venom to be squeezed into the tissue. The stinger, once embedded, remains present. If this has occurred in an eyelid, it may irritate the globe of the eye months after the sting.

The stinging lancets of the wasp are not barbed and can easily be withdrawn by the insect to allow it to reinsert or to escape. It is unusual, therefore, to find a stinger left in place after a wasp sting. The females of the variety called yellow jackets are very aggressive. These insects sometimes bite before stinging.

The venom of bees, wasps, other arthropods contains histamine, basic protein components, free amino acids, hyaluronidase, acetylcholine. Antigenic proteins are species-specific and may lead to cross-reactivity between insects. Symptoms of arthropod stings may vary from minimal erythema to a marked local reaction of severe systemic toxicity (especially from multiple stings). Infection may occur. A generalized allergic reaction has been described that resembles serum sickness.

Early application of ice packs to reduce swelling is indicated. Elevation of the extremity is also useful. Oral antihistamines may be of some use in reducing urticaria. Parenteral corticosteroids may reduce delayed inflammation. If infection occurs, treatment consists of local debridement and antibiotics. Moderately severe reactions after bites of arthropods will present as generalized syncope or urticarial reactions. If an anaphylactic reaction or severe reaction is present, aqueous epinephrine, 0.5–1 mL of 1:1000 solution, should be given intramuscularly. A repeat dose may be given in 5–10 minutes, followed by 5–20 mg of diphenhydramine slowly intravenously. Administration of corticosteroids and general supportive measures such as oxygen administration, plasma expanders, pressor agents may be required in case of shock. Previously sensitized patients should carry identifying tags and a kit for emergency intramuscular injection of epinephrine.

It is possible to immunize persons against bee and wasp stings, but cost-benefit analyses indicate that this is rarely if ever indicated.

Bites of Spiders

While all spiders have poison glands and use venom for killing prey, only a few spider venoms are harmful to humans.

Lactrodectism

The potent venom of this genus acts by destabilization of cell membranes and degranulation at nerve terminals with release of neurotransmitters. Neuromuscular toxic effects of black widow venom occur by presynaptic motor end plate neurotransmitter release.

Intravenous administration of calcium gluconate may relieve muscle pain and spasm, but similar relief can be obtained from intravenous opioids and benzodiazepines. Ice packs may improve localized pain from the bite. Most symptoms are self-limited and, with appropriate supportive therapy, resolve within 48 hours, though full recovery may take over a week. A horse antivenin is available but may cause allergic reactions. Antivenin may be indicated in severely symptomatic patients to speed recovery and perhaps to prevent development of long-term symptoms of bites of arthropods related to neurologic dysfunction.

Loxoscelism

Systemic loxoscelism with intravascular coagulation and renal failure has been seen but is uncommon. The venom appears to cause local tissue necrosis by dissociating normal neutrophil responses of adhesion and degranulation from transmigration and shape changes. Phospholipase D and sphingomyelinase D also contribute to the local necrosis, as well as venom-induced platelet aggregation. Alterations in complement activation and binding of venom to erythrocyte membranes contribute to hemolysis.

Loxoscelism is managed by supportive measures. Cleansing of the bite, rest, and elevation of the affected area are appropriate. While tissue loss is common, early excision of lesions is also associated with poor wound healing. Conflicting data exist regarding systemic treatment with corticosteroids; evidence for efficacy of dapsone (50–100 mg/d) treatment remains anecdotal.

Leave a Reply

Your email address will not be published. Required fields are marked *