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  • Black widow spider bites result in painful muscle spasms, secondary to neurotoxicity, that are responsive to antivenin.
  • Brown recluse spider bites result in hematotoxicity and manifest locally as skin necrosis.
  • Scorpion stings cause severe localized pain with occasional systemic effects in children.
  • Hymenoptera stings from bees and wasps can result in severe anaphylactic reactions and are responsible for more adverse outcomes and fatalities in children than any other arthropods.
  • Fire ant stings can cause painful localized skin reactions.

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In North America, bites and stings by arthropods occur frequently. Approximately 50 000 bites or stings by these species occur annually with about half of these specifically because of spiders. There are more than 30 000 species of spiders, most of which cannot inflict serious bites to humans because of their delicate mouthparts and impotent or prey-specific venoms.1 Most exposures go unnoticed or do not need treatment. Spiders are not known to spread infectious diseases, but certain spiders are known to produce toxic venoms, which can lead to local diseases of the skin, systemic toxicities, or neurological sequelae.

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Anatomy

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The Latrodoctus genus is a common spider found in temperate and tropical areas of the world. The species most common in North America include L. bishopi, L. geometricus, L. hesperus, L. variolus, and L. mactans. Generally speaking, females are 20 times larger, darker in color, and more toxic than their male counterparts. Black widows are described as charcoal or black with eight eyes, eight legs, fangs, poison glands, and a characteristic red hourglass mark on the ventral aspect of the abdomen (Fig. 135–1). Black widows seem to be more prevalent during warmer periods of the year.

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Figure 135-1.
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Female black widow spider with egg sac. www.prevailpest.com.

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Pathophysiology

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The female black widow is generally considered poisonous to humans; whereas the males are not significantly poisonous due to their small jaws and a minimal number of poison glands. Black widows spiders control the amount of venom they inject; an estimated 15% of bites to humans are nonenvenomating.2 The venom's toxicity is due to the α-latrotoxin present in the spider's venom. This toxin facilitates exocytosis of synaptic vesicles and the release of the neurotransmitters norepinephrine, γ-aminobutyric acid, and acetylcholine.3 The toxin also causes degeneration of motor end plates, resulting in denervation. The venom destabilizes nerve cell membranes by opening ion channels, causing a massive influx of calcium into the cell, which may lead to hypocalcemia.

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Clinical Presentation

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Black widow bites usually produce a pinprick sensation but often they go unnoticed. Within the first two hours after the bite, the site may develop redness, cyanosis, urticaria, or a characteristic halo-shaped target lesion. These local symptoms may be followed by generalized symptoms of pain in regional lymph ...

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