Funnel Web Spider Toxicity


Article Author:
Justin Binstead


Article Editor:
Thomas Nappe


Editors In Chief:
David Tauber


Managing Editors:
Avais Raja
Orawan Chaigasame
Carrie Smith
Abdul Waheed
Khalid Alsayouri
Frank Smeeks
Kristina Soman-Faulkner
Trevor Nezwek
Radia Jamil
Patrick Le
Sobhan Daneshfar
Anoosh Zafar Gondal
Saad Nazir
William Gossman
Pritesh Sheth
Hassam Zulfiqar
Navid Mahabadi
Steve Bhimji
John Shell
Matthew Varacallo
Heba Mahdy
Ahmad Malik
Mark Pellegrini
James Hughes
Beata Beatty
Nazia Sadiq
Hajira Basit
Phillip Hynes
Tehmina Warsi


Updated:
12/18/2018 7:49:43 AM

Introduction

There are over 40 species of funnel-web spiders, with 3 genera restricted to Australia, including the Hadronyche, Illawarra, and the Atrax.  Of all Australian spiders, one species of the Atrax genera, the Atrax robustus, is implicated in the most human fatalities. The Atrax robustus is known as the Sydney funnel-web spider and is native to eastern Australia. Funnel-web spiders are medium to large in size and are dark in color, ranging from black to brown. Funnel-web spiders get their name from their funnel-shaped burrows they spin to trap prey. These spiders reside in cool and relatively sheltered habitats. They are often found under rocks or in rock gardens, in various shrubberies, or under logs. Some funnel web spiders even reside in trees, sometimes several meters in the air. The bite of the Sydney funnel-web spider is potentially deadly, but since the development of the antivenom in 1981 and the advancement of modern first aid techniques, there has been only 1 death associated with this spider's bite and was likely a result of a delayed presentation.[1]

Funnel-web spiders have powerful, sharp fangs that have been known to penetrate fingernails and soft shoes. They are known to be the most dangerous spiders in the world. The silk entrance to the burrow of a Sydney funnel-web spider has a "vestibule-like" structure, and the spider sits just within the vestibule and senses vibrations along the silk "trip lines" and reacts to inject venom into its prey. The tree-dwelling funnel-web spiders can reach 4 to 5 cm in length, with the largest species being the Northern Tree Funnel Web Spider.[2]

Etiology

All funnel-web spider bites should be treated as potentially life-threatening, even though only approximately 10% to 15% of bites are venomous. Since the venom from the funnel-web spider bite is highly toxic, all species should be considered potentially dangerous.[3] In all the fatalities where the gender of the spider was confirmed, the male funnel-web spider was responsible. Males are more active at night and have been known to enter homes. The onset of severe envenomation is rapid. In one study, the median time to onset of envenoming was 28 minutes, and only 2 cases had onset after 2 hours. In both cases, the bites had pressure immobilization bandages applied. Death may occur in 15 minutes (small children) to 3 days.[1] Younger patients and patients with underlying medical conditions have a higher incidence of death when they are bitten by a funnel-web spider.

Epidemiology

Data has been extracted to determine the species-specific envenomation rates and the severity of the funnel-web spider bites and to determine both the efficacy and the adverse events related to the antivenom. The data gathered revealed that there were 198 potential funnel-web spider bites identified. Of those, 138 were confirmed as a funnel-web spider, and 77 of those cases produced severe envenomation. All of the species related to the severe envenomations were attributed to species restricted to New South Wales and Southern Queensland. The antivenom was used in 75 patients, including 22 children, with a complete response in 97% of the positively identified cases.[3] There were 3 adverse reactions which were all in adults (one early mild, one early severe that require epinephrine, and a delayed serum sickness reaction). The researchers concluded that severe funnel-web spider envenomations were confined to New South Wales and southern Queensland, with the tree-dwelling funnel webs having the highest envenomation rates. The antivenom to funnel web spiders was safe and effective, and severe allergic reactions are uncommon. True necrotizing arachnidism appears to be quite rare.

Toxicokinetics

There are a large number of different toxins in the venom of these spiders. They are classified as atracotoxin from their subfamily name. These neurotoxins induce the spontaneous and repetitive firing of action potentials in presynaptic autonomic and motor neurons, leading to catecholamine surge. The atracotoxin are also associated with voltage-gated sodium channel toxicity.[4] These are extremely toxic and believed to be the main cause of lethal envenomation syndrome following the bite of a funnel web spider. The venomous component primarily responsible for the envenomation syndrome of the Atrax robustus is a single peptide known as delta-atracotoxin.[5][6]

History and Physical

Early symptoms of a funnel-web spider envenomation include facial paresthesias, nausea, vomiting, profuse diaphoresis, drooling, and shortness of breath. Patients may become agitated, confused and ultimately comatose. This is associated with hypertension, metabolic acidosis, dilated pupils, muscle twitching and pulmonary and cerebral edema. Death results from pulmonary edema or progression to hypotension and circulatory collapse.[7]

Evaluation

There is no lab assay available to detect the venom of a funnel-web spider easily. Laboratory evaluation should include serum creatinine kinase, electrolytes, renal function, glucose; arterial or venous blood gas to assess for hypoxia; and coagulation studies to assess for disseminated intravascular coagulation.

Treatment / Management

The bite from a funnel-web spider can cause very severe symptoms that can worsen and progress rapidly, and the primary treatment is antivenom known as FWSAV. Therefore, all bites from large, black spiders in the endemic areas should be treated as funnel-web spider bites. First-aid treatment for a suspected funnel-web spider envenomation starts with cleansing the area with soap and tap water, then immediately applying a pressure immobilization bandage. This technique combines a light pressure bandage with immobilizing the affected area as if it were being splinted. This technique limits the spread of the venom throughout the body and minimizes the area affected by the bite.[3] There is also evidence suggesting that the applied pressure and prolonged localization inactivate the venom. Emergency medical treatment should be sought as soon as possible. It is critical to maintain the pressure immobilization bandage until the patient is evaluated by trained medical personnel in an emergency department. The pressure immobilization bandage should not be removed prematurely as this can cause systemic mobilization of the venom. Before removal of the pressure immobilization bandage, intravenous access should be established, and the patient should be connected to appropriate cardiorespiratory monitoring, while a supply of antivenom is obtained and readily available for administration. A patient who does not show any symptoms of systemic envenomation may deteriorate rapidly once the bandage is removed.[7] The primary treatment is antivenom FWSAV; however, other supportive measures may be indicated. Antivenom should be given at the earliest sign of systemic envenomation. For patients without any development of systemic symptoms, monitoring should occur for 4 to 6 hours from the time of the envenomation or, if pressure bandage applied, from the time of removal. Antivenom is not indicated if the patient only has localized symptoms after an appropriate observation period.

Differential Diagnosis

Differential diagnosis includes other insect or spider bites, cutaneous abscess (=/-) MRSA, anthrax, herpes zoster, pyoderma gangrenosum, Stevens-Johnson syndrome, and toxic epidermal necrolysis.

Pearls and Other Issues

  • The Atrax robustus is considered the deadliest spider in the world. 
  • Since the development of the antivenom FWSAV in 1981, there have been no reported deaths with early administration.
  • Primary treatment is with antivenom FWSAV.
  • All patients should have immobilizing pressure dressing applied and transported immediately to the nearest emergency department.

Enhancing Healthcare Team Outcomes

Primary consultation should include a medical toxicologist or the local poison center. 

Critical care specialists should be consulted for inpatient monitoring for all symptomatic patients.

Recommended follow-up with healthcare team including primary care, nursing, and medical toxicologist should occur for anyone given antivenom, to assure no development of serum sickness.

All treating physicians and primary providers including nurse practitioners should educate on outdoor safety and close follow-up.


  • Image 7301 Not availableImage 7301 Not available
    Contributed by Steve Bhimji, MS, MD, PhD
Attributed To: Contributed by Steve Bhimji, MS, MD, PhD

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Funnel Web Spider Toxicity - Questions

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All of the spiders that are members of the funnel-web family are native to which country?



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A 17-year-old male is brought to the emergency department for evaluation after he was hiking and was bitten by a large black spider. This occurred in Australia in a region known to be a habitat for funnel-web spiders. What would be the initial management of this patient?



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A 12-year-old boy was bitten by a large black spider in his left arm while reaching under a tree branch for a ball. This occurred during the summer in the northern suburbs of Sydney, Australia. The yard has scattered spider webs in an oddly shaped funnel pattern. What would be the definitive treatment for this patient?



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A 65-year-old Australian male was cleaning his swimming pool when he noticed a large black spider in the water. Assuming the spider was dead, he reached in and grabbed it. He subsequently was bitten by the spider. He calls and requests recommendations on what to do. How should he be instructed?



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A 17-year-old female is hiking in the woods just after a rainstorm. She drops her phone, and as she picks it up, she is bitten in the arm by a spider. She is concerned it is a bite from a funnel-web spider since she's in an area that is a known habitat for these spiders. Which of the following characteristics would help to identify the spider as a funnel-web spider?



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A 40-year-old male is working in the laboratory milking funnel-web spiders in efforts to obtain their venom to be used for producing the antivenom. While performing his duties, he is bitten by a male funnel web spider in his left forearm. It is a painful bite, and he is concerned about the toxin of the funnel-web spider. How does this toxin affect humans?



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Funnel Web Spider Toxicity - References

References

Isbister GK,Gray MR,Balit CR,Raven RJ,Stokes BJ,Porges K,Tankel AS,Turner E,White J,Fisher MM, Funnel-web spider bite: a systematic review of recorded clinical cases. The Medical journal of Australia. 2005 Apr 18     [PubMed]
Atkinson RK,Walker P, The effects of season of collection, feeding, maturation and gender on the potency of funnel-web spider (Atrax infensus) venom. The Australian journal of experimental biology and medical science. 1985 Oct     [PubMed]
Isbister GK, Antivenom efficacy or effectiveness: the Australian experience. Toxicology. 2010 Feb 9     [PubMed]
Del Brutto OH, Neurological effects of venomous bites and stings: snakes, spiders, and scorpions. Handbook of clinical neurology. 2013     [PubMed]
Luch A, Mechanistic insights on spider neurotoxins. EXS. 2010     [PubMed]
Alewood D,Birinyi-Strachan LC,Pallaghy PK,Norton RS,Nicholson GM,Alewood PF, Synthesis and characterization of delta-atracotoxin-Ar1a, the lethal neurotoxin from venom of the Sydney funnel-web spider (Atrax robustus). Biochemistry. 2003 Nov 11     [PubMed]
Braitberg G,Segal L, Spider bites - Assessment and management. Australian family physician. 2009 Nov     [PubMed]

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