Spider Envenomation in Australia
Known species of spiders number tens of thousands worldwide, grouped into over a hundred families and nearly 4000 genera. Millions of toxins are estimated to exist in their venoms but only a very small fraction, several hundred, has been identified and characterized. Protein toxins of lethal potential to humans are present in venoms of Australian genera in the family Hexathelidae (Atrax and Hadronyche, Funnel-web spiders), in the family Actinopodidae (Missulena, Mouse spiders), and the one species of the family Theridiidae (Latrodectus hasselti, Red-back spider). The principal toxins in Atrax and Hadronyche venoms and probably in Missulena venom are δ-hexatoxins (42-residue peptides) which slow the inactivation of voltage-gated sodium channels, cause repetitive action potentials in neural tissue, and subsequent uncontrolled release of neurotransmitters with characteristic clinical syndromes of envenomation. An effective antivenom is available. These toxins have a characteristic internal cystine knot motif conferred by disulfide bonds. Other small peptides in funnel-web spider venoms, ω-hexatoxins, target insect voltage-gated calcium channels while ҡ-hexatoxins target insect calcium-activated potassium channels. The principal toxin in Latrodectus venom is a 1180-residue protein (α-latrotoxin), which forms a tetramer on nerve ending membranes creating pores for the ingress of calcium and subsequent exocytosis of synaptic vesicles and release of transmitters. Internal calcium stores are also released. Envenomation causes a universally recognized constellation of symptoms and signs, “latrodectism” which is effectively treated with antivenom. The syndrome also results from envenomation by Steatoda carpensis (a Cupboard spider), another of the Theridiidea family.
KeywordsSpiders Hexathelidae Atrax Hadronyche Latrodectus Latrodectism Antivenom
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