Redback Spider, Brown House Spider

 First aid for redback spider envenomation is washing the site and analgesia.

The redback spider is the cause of more hospital presentations each year in Australia than any other venomous animal. A closely related species, the brown house spider, is also dangerous, and can cause a clinical picture similar to that caused by the redback, although typically less severe. The following information applies to both species except where the distinction is explicitly drawn.

Signs and Symptoms

• Pain at the bite site
• Local swelling, erythema
• Pain progressing over hours to involve the entire limb, typically persisting for more than 24 hours
• Tender and swollen regional lymph nodes
• Excessive sweating sometimes unassociated areas
• Nausea and vomiting, abdominal pain
• Headache
• Migratory arthralgia
• Fever
• Restlessness and insomnia
• Hypertension, tachycardia
• Neurological symptoms associated with the neuromuscular blockade and possibly excessive catecholamine release caused by q-latrotoxin, e.g., muscle weakness or twitching

Treatment

Pressure immobilisation is not recommended due to the slow progression of symptoms and the fact that they are generally not life-threatening. Furthermore, reducing the movement of venom away from the site might increase the intensity or duration of the local pain.

Opioid analgesics generally only make the patient drowsy without alleviating the pain.

Where antivenom is indicated, it should be administered according to the protocol set out in the next section.

Ensure tetanus status is up to date. Provide education regarding serum sickness.

Antivenom

One ampoule of monovalent Redback Spider Antivenom should be given IM initially and the patient observed for one hour. If the patient has severe signs and symptoms of envenomation, the antivenom should be administered intravenously. Intravenous administration should only be undertaken in a setting where appropriate resuscitation expertise and equipment are available. If the patient has made significant improvement after one hour post-antivenom, they may be discharged home. If the patient's condition has not improved significantly in one hour after antivenom is given, administer a second vial and again observe for one hour. If no significant improvement is observed within this time, consider differential diagnosis. If redback envenomation remains the diagnosis, then consider a third ampoule of antivenom given IV in 100-150 ml crystalloid over 15-30 minutes. If there remains no improvement an hour after the third dose of antivenom, consider admission and 24 hours' observation. Give anxiolytics and analgesics for symptom relief. Cases of envenomation by the brown house spider have been successfully treated with redback antivenom. Redback spider antivenom made by CSL Ltd is equine in origin.

Photo: R. Lowe, AVRU

Last updated: July 2005