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Australian funnel-web spider

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Australian funnel-web spiders are very venomous spiders of the family Hexathelidae,[1] represented by an estimated 40 species of Hadronyche and the sole species of the genus Atrax.[2] A. robustus, the notoriously dangerous Sydney funnel-web spider.

Description

Victorian funnel-web spider Hadronyche modesta

. Like the related diplurid spiders, some hexathelids have long spinnerets; this is especially true of A. robustus.

Like other Mygalomorphae (also called Orthognatha) —an infraorder of spiders that includes the tropical tarantulae[3] —these spiders have fangs which point straight down the body and do not point towards each other (cf Araneomorphae). They have ample venom glands that lie entirely within their chelicerae. Their fangs are large and powerful, capable of penetrating fingernails and soft shoes.

Habitat and distribution

Funnel-webs make their burrows in moist, cool, sheltered habitats—under rocks, in and under rotting logs, some in rough-barked trees (occasionally metres above ground). They are commonly found in suburban rockeries and shrubberies, rarely in lawns or other open terrain. A funnel-web's burrow characteristically has irregular silk trip-lines radiating from the entrance.[1] Unlike some related trapdoor spiders, funnel-webs do not build lids to their burrows.

The primary range of the Australasian funnel-web spiders is the eastern coast of Australia, with specimens found in New South Wales, South Australia, Victoria, and Queensland.[1][4] In addition, some specimens have been found in other islands in the south Pacific. The only Australian states without funnel-webs are Western Australia[5] and the Northern Territory.

Medical significance

Funnel-webs are one of the three most dangerous spiders in the world and are regarded by some to be the most dangerous.[6]

Examination of bite records has implicated wandering males in most if not all fatal bites to humans. Adult males, recognized by the modified terminal segment of the palp, will defend themselves vigorously if they feel threatened and tend to wander during the warmer months of the year looking for receptive females for mating.[7] They are attracted to water and hence are often found in swimming pools where they have fallen while wandering. The spiders can survive such immersion for several hours and can deliver a bite when removed from the water.[8]: p.313-22 . They also show up in garages and yards in suburban Sydney. Contrary to a commonly held belief, no funnel-web spider is able to jump, although they can run quickly.[8]: p.313-22 

While some very venomous spiders may give dry bites, these spiders do so much less frequently.[citation needed] An inefficient mode of delivery (to large animals) and interrupted contact are also possible causes of low volume delivery. It has been claimed that approximately 10% to 25% of bites will produce significant toxicity[6] but the likelihood cannot be predicted and all should be treated as potentially life-threatening.

There have been 26 recorded deaths in Australia in the last 100 years from spider bites. Bites from Sydney funnel-web spiders have caused 13 deaths (seven in children)[6]. In all cases where the sex of the biting spider could be determined, it was found to be the male of the species.[9] Most victims were young, ill or infirm.[citation needed] One member of the genus Hadronyche, the northern tree funnel-web has also been claimed to cause fatal envenomation[4] but, to date, this lacks the support of a specific medical report. Assays of venom from several Hadronyche species have shown it to be similar to Atrax venom.

Toxins

There are many different toxins in the venom of Atrax and Hadronyche spiders. Collectively, these spider toxins are given the name atracotoxins (ACTX), as all these spiders belong to the subfamily Atracinae. The first toxins isolated were the δ-ACTX toxins present in the venom of both A. robustus (δ-ACTX-Ar1, formerly known as robustoxin or atracotoxin) and H. versuta (δ-ACTX-Hv1a, formerly known as versutotoxin). Both these toxins produce the same funnel-web envenoming syndrome in monkeys as that seen in humans, suggesting that they are responsible for the physiological effects seen with crude venom.[9]

Female Sydney funnel-web spider in warning posture

These toxins are thought to operate by opening sodium channels. They are presynaptic neurotoxins that (via sodium channels) induce spontaneous, repetitive firing of action potentials in autonomic and motor neurons and inhibit neurally mediated transmitted release resulting in a surge of endogenous acetylcholine, noradrenaline and adrenaline.[10]

Although extremely toxic to primates, the venom appears to be fairly harmless to many other animals. It has been suggested that these animals may be resistant to the venom's effects due to the presence of IgG, and possibly cross-linked IgG and IgM inactivating factors in their blood plasma that bind to the toxins responsible and neutralise them, or it may involve a non-specific reaction due to the highly basic nature of the toxins.[11]

The female venom was thought to be only about a sixth as potent to humans as that of the male[12] but recent research has proven that false.[citation needed] The bite of a female or juvenile may be serious; however, considerable variability occurs in venom toxicity between species, together with assumable degrees of inefficiency in the method of venom delivery.

Symptoms

Envenoming symptoms observed following bites by these spiders are very similar. The bite is initially very painful, due to the acidity of the venom and the size of the fangs penetrating the skin. Systemic envenoming may follow the local effects. Early symptoms of systemic envenoming include tingling around the mouth and tongue, facial muscle twitching, nausea, vomiting, profuse sweating, salivation, and shortness of breath. Patients may rapidly develop agitation, confusion and coma associated with hypertension, metabolic acidosis, dilation of the pupils, generalised muscle twitching and pulmonary oedema.[6] Death results from progressive hypotension or possibly raised intracranial pressure consequent on cerebral oedema.[13]

The onset of severe envenoming can be rapid. In one prospective study, the median time to onset of envenoming was 28 minutes, with only two cases having onset after 2 hours (both had pressure immobilization bandages applied).[6] Death may occur within a period ranging from 15 minutes[9] (this occurred when a small child was bitten) to three days.

Treatment

First aid for funnel-web bites consists of applying a pressure immobilization bandage. Pressure immobilization is the wrapping of the bitten limb with a crepe bandage and splint. It was originally developed for snakebites but has been shown to be effective at slowing venom movement in funnel-web bites and may also slowly inactivate the venom.[14]

Further supportive care may be necessary, but the mainstay of treatment is antivenom. Antivenom is raised against male Atrax robustus venom but appears to be effective for all species of funnel web spiders.[15] Funnel-web antivenom has also been shown to reverse the in vitro effects of Eastern Mouse spider (Missulena bradleyi) venom.[16]

Prior to the introduction of antivenom, envenoming resulted in significant morbidity and mortality.[17] The purified rabbit IgG antivenom was developed in 1981 through a team effort led by Dr Struan Sutherland, head of immunology at the Australian Commonwealth Serum Laboratories in Melbourne.[18] Fortunately, the antivenom is fast-acting and highly and globally effective.[19] Antivenom therapy has shortened the course of envenoming: prior to antivenom availability, the average length of hospital treatment for severe bites was about 14 days. Today, antivenom-treated patients are commonly discharged from hospital within 1 to 3 days.[9] There have been no known deaths since it became available.[6]

Species

See also: List of Hexathelidae species

Many species are yet to be named. The following named species are referred to by the common name of funnel-web:

Footnotes

  1. ^ a b c Funnel-web Spiders at the Australian Museum, Sydney
  2. ^ Platnick N I World Spider Catalog (2008). The following others were reassigned in 1988 from Atrax to the genus Hadronyche: A. adelaidensis, A. eyrei, A. flindersi, A. formidabilis, A. infensa, A. modesta, A. pulvinator, A. valida, A. venenata and A. versuta.
  3. ^ Mygalomorph tarantulas are a different family from the original 'tarantula', an araneomorph lycosid from Europe. —Rod and Ken Preston-Mafham. Spiders of the World. Blandford Press, 1989, England, p. 47
  4. ^ a b Fact sheet: Funnel-web spider CSIRO Note: Though formerly well resourced in entomology, CSIRO acknowledges on this site that it currently does no research into funnel-web spiders.
  5. ^ Raymond Mascord Australian Spiders in Colour Reed Press NSW, 1991, p. 14
  6. ^ a b c d e f Isbister G, Gray M, Balit C, Raven R, Stokes B, Porges K, Tankel A, Turner E, White J, Fisher M (2005). "Funnel-web spider bite: a systematic review of recorded clinical cases". Med J Aust. 182 (8): 407–11. PMID 15850438.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  7. ^ Isbister G, Gray M (2004). "Bites by Australian mygalomorph spiders (Araneae, Mygalomorphae), including funnel-web spiders (Atracinae) and mouse spiders (Actinopodidae: Missulena spp)". Toxicon. 43 (2): 133–40. doi:10.1016/j.toxicon.2003.11.009. PMID 15019472.
  8. ^ a b Gray M. The Distribution of Funnel-Web Spiders in Australia in Toxic Plants and Animals: A Guide for Australia. Queensland Museum Press, 1987. Page 313-22
  9. ^ a b c d Nicholson G, Graudins A (2002). "Spiders of medical importance in the Asia-Pacific: atracotoxin, latrotoxin and related spider neurotoxins". Clin Exp Pharmacol Physiol. 29 (9): 785–94. doi:10.1046/j.1440-1681.2002.03741.x. PMID 12165044.
  10. ^ Harris J, Sutherland S, Zar M (1981). "Actions of the crude venom of the Sydney funnel-web spider. Atrax robustus on autonomic neuromuscular transmission". Br J Pharmacol. 72 (2): 335–40. PMID 6260279.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  11. ^ Sheumack D, Comis A, Claassens R, Mylecharane E, Spence I, Howden M (1991). "An endogenous antitoxin to the lethal venom of the funnel web spider, Atrax robustus, in rabbit sera". Comp Biochem Physiol C. 99 (1–2): 157–61. doi:10.1016/0742-8413(91)90093-9. PMID 1675965.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  12. ^ Wiener S. "The Sydney funnel-web spider (Atrax robustus): II. Venom yield and other characteristics of spider in captivity". Med J Aust. 46(2): 678–82. PMID 13844638.
  13. ^ Torda T, Loong E, Greaves I (1980). "Severe lung oedema and fatal consumption coagulopathy after funnel-web bite". Med J Aust. 2 (8): 442–4. PMID 7010098.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  14. ^ Sutherland S, Duncan A (1980). "New first-aid measures for envenomation: with special reference to bites by the Sydney funnel-web spider (Atrax robustus)". Med J Aust. 1 (8): 378–9. PMID 6771503.
  15. ^ Graudins A, Wilson D, Alewood P, Broady K, Nicholson G (2002). "Cross-reactivity of Sydney funnel-web spider antivenom: neutralization of the in vitro toxicity of other Australian funnel-web (Atrax and Hadronyche) spider venoms". Toxicon. 40 (3): 259–66. doi:10.1016/S0041-0101(01)00210-0. PMID 11711122.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  16. ^ Rash L, Birinyi-Strachan L, Nicholson G, Hodgson W (2000). "Neurotoxic activity of venom from the Australian eastern mouse spider (Missulena bradleyi) involves modulation of sodium channel gating". Br J Pharmacol. 130 (8): 1817–24. doi:10.1038/sj.bjp.0703494. PMID 10952670.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  17. ^ Isbister G, Graudins A, White J, Warrell D (2003). "Antivenom treatment in arachnidism". J Toxicol Clin Toxicol. 41 (3): 291–300. doi:10.1081/CLT-120021114. PMID 12807312.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  18. ^ Fisher M, Raftos J, McGuinness R, Dicks I, Wong J, Burgess K, Sutherland S (1981). "Funnel-web spider (Atrax robustus) antivenom. 2. Early clinical experience". Med J Aust. 2 (10): 525–6. PMID 7321948.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  19. ^ Hartman L, Sutherland S. "Funnel-web spider (Atrax robustus) antivenom in the treatment of human envenomation". Med J Aust. 141 (12–13): 796–9. PMID 6503783.


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