Sydney Funnel Web
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The Australian funnel web spiders comprise approximately 35 species within 2 genera, Atrax and Hadronyche. The common name arises from the funnel-like entrance to their silk-lined burrow retreats, although the burrows more commonly resemble a tube. The Sydney funnel web spider (Atrax robustus) is the only species known to have caused death in humans; however, bites from other funnel web spiders have caused serious envenomation and clearly have the potential to cause death.
Bites from these spiders are remarkable in 2 respects. First, the venom affects man and monkeys far more than other creatures. Man and monkeys lack a naturally occurring inhibitor of the venom that is present in many nonprimate vertebrates. Second, only the bite from the male appears to be dangerous, which is a reversal of the situation with other highly poisonous spiders. Venom toxicity is consistently several times higher in the male than in the female (although females secrete several times more toxin). The male behaviour pattern of permanently leaving the burrow to seek a mate leads it to enter houses and find its way into clothing and bedding.
Many of the effects of robustotoxin are predictable from their neurotoxic actions. Skeletal muscle spasms, fasciculationís, and patchy weakness occur because of effects on the peripheral nervous system. Autonomic stimulation causes excessive secretions, piloerection, tachycardia, hypertension, and cardiac arrhythmias. Hypertension progresses to hypotension, presumably because of catecholamine depletion and/or impaired catecholamine release. Unconsciousness may occur because of hypoxia and hypotension or raised intracranial pressure, the cause of which is uncertain.
Venom reaches the circulation rapidly (approximately 2 min) after subcutaneous injection.
It has been estimated that 30-40 cases of funnel web spider bite occur each year in eastern and southern Australia.
Death occurs between 15 minutes and 3 days following the bite. In children, fatality is usually early and caused by pulmonary oedema, whereas, in adults, fatality is usually later and caused by persistent hypotension or other complications. The spider usually is seen, and its bite is extremely painful for hours to days (the fangs are large and enter with considerable force).
- Perioral tingling occurs within 15 minutes; other symptoms include the following:
- Tongue spasms
- Abdominal pain
- Severe breathing problems
- Muscle fasciculationís and spasms are common.
- Unconsciousness may occur, but it appears to be uncommon as a primary event.
- Cardiac arrhythmias and cardiac arrest may occur.
- Severe pulmonary oedema occurs early and may be fatal.