FUNNEL WEB SPIDERS (ATRAX)

BACKGROUND

Australian funnel web spiders are capable of inducing a severe and potentially fatal neurotoxic envenomation syndrome. Unlike other species of the spiders, funnel web spiders can bite tenaciously and may have to be physically removed from the victim. They prefer to live on the ground in moist, temperate environments such as burrows, crevices between rocks, and near the foundations of homes. They are named for the tubular or funnel-shaped web they build.18

PATHOPHYSIOLOGY

The lethal component of funnel web spider venom is robustotoxin. It induces an autonomic storm by causing excessive release of acetylcholine, norepinephrine, and epinephrine.19,20

CLINICAL MANIFESTATIONS

Funnel web spider envenomation causes a biphasic envenomation syndrome. The first phase includes pain at the bite site, perioral tingling, piloerection, and regional fasciculations which may progress to muscle spasm. This muscle spasm may involve the face, tongue, and larynx leading to airway compromise. The increased stimulation of cholinergic and adrenergic systems causes nausea, vomiting, lacrimation, salivation, tachycardia, hypertension, cardiac dysrhythmias, and acute lung injury. Acute lung injury is the predominate cause of death during the first phase.20

In the second phase the symptoms of the first phase resolve and lead to the gradual onset of refractory hypotension, apnea, and cardiac arrest.20

TREATMENT

Prehospital management consists of pressure immobilization using an elastic crepe bandage applied tightly enough to limit lymphatic spread, but not to restrict blood flow. The venom of the funnel web spider is one of the few animal venoms to undergo local inactivation. The patient should be transported to the nearest medical facility with the bandage in place, and the bandage should not be removed until antivenom is readily available to be administered.21

An effective funnel web spider antivenom is available in Australia. An initial dose of 2 vials is indicated for patients with signs of envenomation, while a dose of 4 vials is indicated for pulmonary edema or decreased mental status. The initial dose is repeated every 15 minutes until the patient clinically improves. A dose of 8 vials is commonly reported in cases of severe envenomation.21