AUTHOR AND EDITOR INFORMATION

Section 1 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

INTRODUCTION

Section 2 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Background

The redback spider (Latrodectus hasseltii) belongs to the family Theridiidae, the comb-footed spiders. Its genus Latrodectus also includes black widows, whose name may be more familiar to North American readers. The redback spider can be found throughout Australia, although it is more commonly seen in the temperate regions than the colder, southern areas. The spider exists in higher numbers in Australia's urban and suburban areas and is virtually absent in the continent's forests. Outside of Australia, similar species of Latrodectus include Karakurt in the Central Asia, Malmignatte in Europe, the Koppie spider in South Africa, and the Night Stinger in New Zealand.

The redback spider bite is the most common envenomation requiring antivenom in Australia. The female redback spider is responsible for most occurrences of envenomations. She is usually 10 mm in length and has a small cephalothorax and a large, globular abdomen that bears a red, orange, or brown stripe. The male redback spider is considerably smaller than the female and is only occasionally able to cause mild envenomation.

Pathophysiology

The redback spider can cause a clinical condition referred to as latrodectism following a bite. The active ingredient in the redback's venom responsible for its toxic properties in vertebrates is a 130-kd protein, alpha-latrotoxin (aLTX). A potent neurotoxin, aLTX aggregates into tetramers that form pores in neuronal presynaptic cell membranes allowing calcium influx into the cytosol and resulting in exocytosis of neurotransmitters. The membrane pores formed by aLTX may also be large enough for a direct efflux of small intracellular compounds that are vital for cytoplasm function.

The monomeric aLTX can also act by activating latrophilin (LPH), an aLTX receptor found on the cell surface of neuronal cells, without incorporating into the cell membrane. LPH is a G protein-coupled receptor that activates phospholipase C, which, in turn, increases the cytosolic concentration of IP3 leading to release of calcium from intracellular stores. This rise in cytosolic calcium increases the rate of spontaneous exocytosis of neurotransmitters and the amplitude of evoked release. Alpha-latrotoxin is a potent venom with an LD-50 in mice, which is 20-40 µg/kg of body weight.

Frequency

United States

Only the black widow spider, a close relative of the redback spider, lives in the United States. These arachnids cause approximately 2500 envenomations each year.

International

The redback spider is found in Australia, New Zealand, and southern Asia. In Australia, the spider has been blamed for 250 envenomations requiring antivenom annually. Perhaps many more cases are mild or unrecognized and do not receive antivenom.

Race

All races are susceptible to redback spider envenomation if the patient lives in an endemic area inhabited by the redback spider.

Sex

In one study of redback envenomations in Australia, 60% of victims were female. However, most other sources do not quote a male/female sex discrepancy.

Age

Redback envenomation may occur at any age; the median age is 35 years. Envenomation may be more dangerous in babies and small children because of the difficulty in making a specific diagnosis in that group of patients in addition to the small body size bearing the same dose of injected poison as an adult would tolerate.

CLINICAL

Section 3 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

History

• In Australia, most bites occur during the warmer months between December and April. Bites to the limbs comprise approximately three quarters of cases, and bites to the distal limbs are twice as common as to the proximal limbs.
• The cardinal symptoms of redback spider envenomation include immediate pain at the site of the bite with or without erythema, which usually progresses over hours to involve the entire limb and draining lymph nodes in the axilla or groin. The pain may persist longer than 24 hours with a median duration of 36 hours. Other common complaints include nausea, vomiting, abdominal pain, headache, and migratory arthralgias.
• In infants, nonspecific symptoms may be present, including inconsolable crying and refusal to eat.
• Most cases are mild or unrecognized and do not receive antivenom. The only way to accurately diagnose a redback spider bite is for the patient to recognize the typical markings on the spider's abdomen or bring the spider in with the patient for proper identification.

Physical

• Common physical findings in a patient with redback spider envenomation include tenderness and erythema at the bite site. Occasionally, one can see localized or generalized sweating, which may be unrelated to the bite site. Local piloerection may also be present.
• Systemic findings in redback spider envenomation, seen in approximately 35% of all bites, include fever, hypertension, and tachycardia.
• Neurological symptoms may include restlessness and insomnia, muscle weakness and twitching, and paralysis. The median duration of all effects is 48 hours.
• Rare complications include myocarditis, rhabdomyolysis, and death.

DIFFERENTIALS

Section 4 of 11  

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• Follow-up
• Miscellaneous
• Multimedia
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Other Problems to be Considered

Redback spider envenomation has been mistaken for sepsis, acute abdomen, acute hepatitis, testicular torsion, anaphylaxis, and premature labor.

WORKUP

Section 5 of 11  

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• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Lab Studies

• The serum creatine kinase level may be elevated if the kidneys are involved, and peripheral white blood cell count may also be elevated.
• In a female patient, a pregnancy test may be useful to differentiate the presentation from premature labor and to guide the medication choice for treatment of latrodectism.

Imaging Studies

• Plain radiographs of the affected limb may be indicated to evaluate for subcutaneous air if a concern for necrotizing fasciitis exists.
• Venous Doppler ultrasonography of the affected extremity may be indicated to evaluate for deep vein thrombosis.

Other Tests

• ECG may be prove helpful in a patient with autonomic instability, chest pain, or if comorbidities are present.

TREATMENT

Section 6 of 11  

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• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Prehospital Care

• Pressure immobilization of the bitten limb is not recommended due to the slow and non–life-threatening progression of symptoms.
• Ice packs to the bite site and simple oral analgesia may be helpful.
• Do not administer antivenom in the field due to the risk of a severe allergic reaction.
• Collection of the spider may aid its proper identification at the emergency department.

Emergency Department Care

• In patients with severe symptoms and signs of envenomation, treatment with redback spider antivenom should be considered. The benefit of treatment with antivenom should be weighed against the risk of its possible complications, including but not limited to, anaphylaxis and serum sickness.

Consultations

• The local poison control center may be consulted for spider identification and management of severe envenomations.
• A surgeon may be consulted if compartment syndrome is suspected.

MEDICATION

Section 7 of 11  

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Most cases of redback spider envenomation are mild and can be managed symptomatically using common oral analgesics and sedatives.

Redback spider antivenom provides specific treatment in severe cases of envenomation.

Ensure that the patient's tetanus status is up to date.

Drug Category: Antivenom

Redback spider antivenom is the mainstay of treatment of latrodectism. Before the introduction of the antivenom in 1995, 14 deaths due to redback spider envenomation were documented in Australia. The antivenom consists of equine IgE fragments raised against aLTX. Each ampule contains 500 units of neutralizing capacity against the Australian redback spider venom, with an average volume of 1-1.5 mL per ampule. The antivenom is usually administered by intramuscular injection. Indications for use of antivenom include severe headache, vomiting, abdominal pain, hypertension, arthralgia, or myalgia.

Increasing concerns exist about the possible ineffectiveness of the IM route of administration of the redback antivenom. In Mexico and South Africa, the Latrodectus antivenom, which is chemically similar to the redback antivenom, is administered via the IV route. Studies comparing the effectiveness of the IV and IM routes for redback antivenom are underway in Australia.

The risk of allergic reaction to the antivenom is 0.5% and is higher in patients with a history of horse allergy or prior exposure to equine immunoglobulin. Before using the antivenom, ensure the ability to manage hypersensitivity reaction and check for availability of the appropriate resuscitation/intubation equipment. The risk of serum sickness after exposure to the antivenom is 1.4%.

Drug Category: Analgesics

Patients may experience severe pain at the bite site, and pain control is essential to quality patient care.

Drug Name	Morphine sulfate, injectable (Duramorph, Infumorph, Astramorph).
Description	DOC for narcotic analgesia because of its reliable and predictable effects, safety profile, and ease of reversibility with naloxone. Morphine sulfate administered IV may be dosed in a number of ways and commonly is titrated to the desired effect.
Adult Dose	2-10 mg IV administered over 4-5 min or 5-20 mg IM/SC q4-6h prn
Pediatric Dose	0.1-0.2 mg/kg IV/IM/SC q2-4h (not to exceed 15 mg/dose)
Contraindications	Documented hypersensitivity to morphine; asthma, hypotension, respiratory depression, upper airway obstruction, paralytic ileus
Interactions	May cause severe respiratory depression when used with other CNS depressants; phenothiazines may antagonize the analgesic effects of opiates
Pregnancy	C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Precautions	Concurrent administration of other opioid analgesics or CNS depressants, alcohol consumption, circulatory shock, head injury or increased intracranial pressure, respiratory compromise, atrial flutter and other supraventricular tachycardias, elderly and debilitated patients

Drug Category: Benzodiazepines

Patients may experience significant restlessness and anxiety, which may require the use of sedatives for symptomatic control.

Drug Name	Diazepam (Valium)
Description	Modulates postsynaptic effects of GABA-A transmission, resulting in an increase in presynaptic inhibition. Appears to act on part of the limbic system, the thalamus, and hypothalamus, to induce a calming effect. Also has been found to be an effective adjunct for the relief of skeletal muscle spasm caused by upper motor neuron disorders. Rapidly distributes to other body fat stores. Twenty minutes after initial IV infusion, serum concentration drops to 20% of C. Individualize dosage and increase cautiously to avoid adverse effects.
Adult Dose	2-10 mg IM/IV q3-4h prn (not to exceed 30 mg/8 h)
Pediatric Dose	0.04-0.2 mg/kg IV/IM q2-4h prn (not to exceed 0.6 mg/kg/8 h)
Contraindications	Documented hypersensitivity; acute narrow-angle glaucoma; untreated open-angle glaucoma; hypotension; severe respiratory depression
Interactions	CNS toxicity increases when concurrently used with other CNS depressants
Pregnancy	D - Fetal risk shown in humans; use only if benefits outweigh risk to fetus
Precautions	Concurrent use of other CNS depressants, respiratory depression, elderly/debilitated patients, hepatic insufficiency, depressed patients

Drug Name	Midazolam (Versed)
Description	Because water soluble, takes approximately 3 times longer than diazepam to peak EEG effects. Thus, clinician must wait 2-3 min to fully evaluate sedative effects before initiating procedure or repeating dose. Has twice the affinity for benzodiazepine receptors than diazepam. May be administered IM if unable to obtain vascular access.
Adult Dose	0.01-0.05 mg/kg (usually 0.5-4 mg, up to 10 mg) IV slowly over several min; may repeat q10-15min until adequate response achieved
Pediatric Dose	<32 weeks: 0.5 mcg/kg/min IV infusion >32 weeks: 1 mcg/kg/min IV infusion Children: 0.05-0.2 mg/kg IV over 2-3 min, followed by 1-2 mcg/kg/min continuous infusion
Contraindications	Documented hypersensitivity; preexisting hypotension; narrow-angle glaucoma; sensitivity to propylene glycol (diluent)
Interactions	Sedative effects may be antagonized by theophyllines; narcotics, cimetidine, ethanol, and erythromycin may accentuate sedative effects because of decreased clearance; reduce dose of thiopental by 15% when using together
Pregnancy	D - Fetal risk shown in humans; use only if benefits outweigh risk to fetus
Precautions	Caution in congestive heart failure, pulmonary disease, renal impairment, hepatic failure, neuromuscular disease, hypotension, and in elderly patients; monitor for respiratory depression with high or repeated doses; consider lower dosages in patients with organic brain syndrome and patients who may have inhibition of benzodiazepine metabolism and clearance (eg, using nicotine, taking cimetidine)

Drug Category: Immunizations

Tetanus immunization should be administered following a redback spider bite. A booster vaccination is recommended in previously immunized individuals.

FOLLOW-UP

Section 8 of 11  

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• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Further Inpatient Care

• Hospitalization is generally not required, after a period of observation, for patients whose symptoms have been alleviated with antivenom. Patients who have contraindications to antivenom and those requiring large doses of opioid analgesics and sedatives for symptomatic control should be hospitalized. Hospitalization should be considered in the following situations:
• • Pregnant women
  • Severely symptomatic children
  • Elderly patients with significant comorbidities
  • Patients who develop anaphylaxis to antivenom
  • Patients with unusual complications of envenomation

Further Outpatient Care

• Patients should be given thorough instructions listing the symptoms of serum sickness (fever, pruritus, and arthropathy) and infection and advised to seek medical care if such symptoms occur.

In/Out Patient Meds

• Patients may need to undergo a short course of steroid treatment should serum sickness occur.

Deterrence/Prevention

• Use of pesticides may prevent exposure to spiders in the home. In endemic areas, patients should be advised to inspect their clothes and shoes for spiders before wearing them.

Complications

• Hypertensive emergency
• Acute myocardial infarction
• Myocarditis
• Rhabdomyolysis
• Paralysis
• Death
• Antivenom-associated complications
• • Anaphylaxis (type I hypersensitivity reaction) is characterized by urticaria, wheezing, and circulatory collapse. The risk of allergic reaction in patients receiving redback antivenom is 0.5% and is higher in patients with prior exposure to horse serum proteins or history of reactive airway disease. Anaphylaxis is treated with epinephrine, corticosteroids, antihistamines, intravenous fluids, and ventilatory support in the usual medical fashion.
  • Serum sickness (type III hypersensitivity reaction) is characterized by fever, urticaria, pruritus, nephritis, and arthritis. This condition occurs in 1.4% of patients receiving antivenom and is self-limiting. Treatment is usually conservative. Antihistamines and topical steroids may be used for dermatitis and aspirin for arthralgia. In severe reactions, including glomerulonephritis, corticosteroid therapy may be necessary.

Prognosis

• Most patients with redback spider envenomation recover fully.

Patient Education

• Following web sites contain additional information and photographs on redback spider:
• • CSIRO Entomology Web site
  • eMedicine's Consumer Health Bites and Stings Center
  • Museum Victoria Web site

MISCELLANEOUS

Section 9 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Medical/Legal Pitfalls

• Administration of antivenom may require informed consent.
• Discharging a patient who subsequently returns with persistent symptoms requiring antivenom treatment and/or admission may constitute a legal pitfall.
• Administration of antivenom to a patient with a documented prior hypersensitivity to horse serum or history of asthma and multiple medication allergies, who subsequently develops anaphylaxis may serve as grounds for malpractice.

MULTIMEDIA

Section 10 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Media file 1:  Female redback spider showing a distinctive red stripe over the abdomen. Image courtesy of John Paterson.
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Media file 2:  Female redback spider with egg sacs. Image courtesy of John Paterson.
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Media file 3:  Female redback spider. Image courtesy of John Paterson.
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Media file 4:  Female redback spider. Image courtesy of John Paterson.
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REFERENCES

Section 11 of 11

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

• Isbister GK. Failure of intramuscular antivenom in Red-back spider envenoming. Emerg Med (Fremantle). Dec 2002;14(4):436-9. [Medline].
• Ushkaryov YA, Volynski KE, Ashton AC. The multiple actions of black widow spider toxins and their selective use in neurosecretion studies. Toxicon. Apr 2004;43(5):527-42. [Medline].
• White J. CSL Antivenom Handbook. 2nd ed. 2001. Available at http://www.toxinology.com/generic_static_files/cslb_index.html.
• Wiener S. Latrodectism: a prospective cohort study of bites by formally identified redback spiders. Med J Aust. Oct 20 2003;179(8):455; author 455-6. [Medline].

Article Last Updated: Jan 8, 2007