Australasian funnel-web spider

From Wikipedia, the free encyclopedia

Venomous funnel-web spiders

Female Sydney funnel-web spider

Scientific classification

Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Arachnida
Order:	Araneae
Suborder:	Mygalomorphae
Family:	Hexathelidae Simon, 1892

Genera

Atrax
Hadronyche

Australasian funnel-web spiders are venomous spiders of the family Hexathelidae. These spiders are found in two genera of the family: Hadronyche (which is not associated with any known human fatalities) and Atrax (which is known to have killed 13 people). They are notorious for the inclusion of the Sydney funnel-web spider (Atrax robustus) native to eastern Australia. There are other genera in family Hexathelidae, but these don't have the notorious reputation of the Australasian funnel-webs.

1 Description
2 Range, habitat, and diet
3 Medical significance
4 Species
5 Images
6 Footnotes
7 References
8 External links

[edit] Description

These spiders are medium-to-large in size, with body lengths ranging from 1cm to 5cm (0.4" to 2"). They are darkly colored, ranging from black to brown, with a glossy carapace covering the front part of the body. Like the related diplurid spiders, the hexathelids generally have long spinnerets; this is especially true of A. robustus.

Like other Mygalomorphae, (also called the Orthognatha an infraorder of spiders which includes the true tarantulas), these spiders have fangs which point straight down and do not cross each other (cf Araneomorphae). They have ample venom glands that lie entirely within their chelicerae. Their chelicerae and fangs are large and powerful. Although they are rather small compared to the true tarantulas, they should not be handled without taking substantial precautions because their fangs have been known to penetrate fingernails and soft shoes, resulting in dangerous bites.

[edit] Range, habitat, and diet

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. In addition, some specimens have been found in other islands in the south Pacific.

[edit] Medical significance

Funnel-webs are probably one of the three most dangerous spiders in the world and are regarded by some to be the most dangerous.^[1]

Examination of bite records seems to indicate that wandering males have caused a large majority of fatal bites to humans. Males, recognised by the modified terminal segment of the palp, are aggressive and tend to wander during the warmer months of the year looking for receptive female of their kind for mating.^[2] They are attracted to water and hence are often found in swimming pools where they have fallen while wandering. They also show up in garages and yards in suburban Sydney.

While some very venomous spiders may give dry bites, these spiders do so much less frequently. (For a comparison of the toxicity and amounts injected of various spider venoms, see spiders having medically-significant venom.) It appears that approximately 10% to 25% of bites will produce toxicity^[1] 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 funnel web spiders have caused 13 deaths (seven in children),^[1] in all cases where sex could be determined, it was found to be the male of the species.^[3] Most victims were young, ill or infirm. Members of the genus Hadronyche may also cause fatal envenomations although none have been recorded. Assays of venom from several Hadronyche species have shown it to be similar to Atrax venom.

[edit] Toxins

There is a large number of different toxins in the venom of Atrax and Hadronyche spiders, overall they 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) and H. versuta (δ-ACTX-Hv1a, formerly known as versutoxin). Both these toxins produce the funnel web envenoming syndrome in monkeys which is the same as that seen in humans, suggesting that they are responsible for the physiological effects seen with crude venom.^[3]

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 inhibits neurally mediated transmitted release resulting in a surge of endogenous acetylcholine, noradrenaline and adrenaline.^[4]

Although extremely toxic to primates, the venom appears to be fairly harmless to many other animals, including dogs, cats, horses, rabbits, guinea-pigs, chickens and even cane toads. 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 neutralize them, or it may involve a non-specific reaction due to the highly basic nature of the toxins.^[5]

The female venom was thought to be only about a sixth as potent to humans as that of the male^[6] but recent research has proven that false. The bite of a female or juvenile may be serious; however, considerable variability occurs in venom toxicity between species.

[edit] Symptoms

The envenoming syndromes observed following bites by all these spiders are identical. 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.^[1] Death results from progressive hypotension or possibly raised intracranial pressure resulting from cerebral oedema.^[7]

The onset of severe envenoming is 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).^[1] Deaths may occur within a period ranging from 15 minutes^[3] (this occurred when a small child was bitten) to three days.

[edit] Treatment

First aid for funnel web bites consists of applying a pressure immobilisation bandage. Pressure immobilisation 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 retarding venom movement in funnel web bites and may also actually slowly inactivate the venom.^[8]

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.^[9] Funnel web antivenom has also been shown to reverse the in vitro effects of Eastern Mouse spider (Missulena bradleyi) venom.^[10]

Prior to the introduction of antivenom envenoming resulted in significant morbidity and mortality.^[11] The purified rabbit IgG antivenom was developed in 1981 through a team effort led by Dr Struan Keith Sutherland (17 June 1936 - 11 Jan 2002), head of immunology at the Australian Commonwealth Serum Laboratories in Melbourne.^[12] Fortunately, the antivenom is fast-acting and highly and globally effective.^[13] 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, nowadays antivenom-treated patients are commonly discharged from hospital within 1 to 3 days.^[3] There have been no deaths since it became available.^[1]

[edit] Species

The following funnel-web species have been identified:

Atrax robustus, Sydney funnel-web spider
Hadronyche adelaidensis, Adelaide funnelweb spider
Hadronyche cerberea, Tree funnelweb spider or Southern funnelweb spider
Hadronyche eyrei, Eyre Peninsula funnelweb spider
Hadronyche flindersi, Flinders funnelweb spider
Hadronyche formidabilis, Northern Rivers funnelweb spider or Northern funnelweb spider
Hadronyche infensa, Toowoomba funnelweb spider or Fraser Island funnelweb spider.
Hadronyche modesta, Victorian funnelweb spider
Hadronyche pulvinator, Cascade funnelweb spider
Hadronyche venenata, Tasmanian funnelweb spider
Hadronyche versuta, Blue Mountains funnelweb spider

See List of Hexathelidae species for a complete list of species within this family (about 90 species in 11 genera).

[edit] Images

Victorian Funnelweb Spider

Atrax robustus

Also called the Sydney Funnelweb Spider

Female

[edit] Footnotes

^ ^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.
^ 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. PMID 15019472.
^ ^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. PMID 12165044.
^ 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.
^ 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. PMID 1675965.
^ 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.
^ 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.
^ 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.
^ 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. PMID 11711122.
^ 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. PMID 10952670.
^ Isbister G, Graudins A, White J, Warrell D (2003). "Antivenom treatment in arachnidism.". J Toxicol Clin Toxicol 41 (3): 291-300. PMID 12807312.
^ 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.
^ 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.