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Spider Envenomation, Redback
Updated: Sep 23, 2009
Introduction
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 in 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 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.1,2
Female redback spider showing a distinctive red stripe over the abdomen. Image courtesy of John Paterson.
Female redback spider with egg sacs. Image courtesy of John Paterson.
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). aLTX is a potent neurotoxin that works in 2 ways to produce efflux of neurotoxins from presynaptic nerve cells.
In one mechanism of action, aLTX aggregates into tetramers that form pores in neuronal presynaptic cell membranes allowing calcium influx into the cytosol and resulting in exocytosis of neurotransmitters such as norepinephrine, dopamine, acetylcholine, glutamate, and GABA. 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. Latrophilin 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.3,4,5
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.
Mortality/Morbidity
Accurate data regarding morbidity/mortality is difficult to gather, as there is no mandatory reporting of spider bites in Australia. There appears to be greater morbidity in pediatric and elderly patients. There have been no recorded deaths caused by redback spider bites in the past several decades.6
Race
All races are susceptible to redback spider envenomation if the patient lives in an endemic area inhabited by the redback spider. One article shows more severe envenomation in Aboriginal patients, but states that this is due to a significantly longer time from envenomation to presentation in ED as compared to non-Aboriginal patients.7
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.8
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.8
Clinical
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; 46% in distal extremity and 26% in proximal limb.8
- 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.3
- 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.8
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.8
- Systemic findings in redback spider envenomation, seen in approximately 35% of all bites, include fever, hypertension, and tachycardia.8
- 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.
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References
White J. CSL Antivenom Handbook. 2nd ed. 2001. Available at http://www.toxinology.com/generic_static_files/cslb_index.html.
Nimorakiotakis B, Winkel KD. Spider bite--the redback spider and its relatives. Aust Fam Physician. Mar 2004;33(3):153-7. [Medline]. [Full Text].
Graudins A. Widow spider envenomation: Lactrodectism. In: Dart RC, ed. Medical Toxicology. 3rd ed. Lippincott Williams & Wilkins; 2003:1592-1595/248. [Full Text].
Nicholson GM, Graudins A. Spiders of medical importance in the Asia-Pacific: atracotoxin, latrotoxin and related spider neurotoxins. Clin Exp Pharmacol Physiol. Sep 2002;29(9):785-94. [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].
Australian Museum. Available at http://australianmuseum.net.au/Redback-Spiders.
Mollison L, Liew D, McDermott R, Hatch F. Red-back spider envenomation in the red centre of Australia. Med J Aust. Dec 5-19 1994;161(11-12):701, 704-5. [Medline].
Isbister GK, Gray MR. 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].
Isbister GK, Brown SG, Miller M, Tankel A, Macdonald E, Stokes B, et al. A randomised controlled trial of intramuscular vs. intravenous antivenom for latrodectism--the RAVE study. QJM. Jul 2008;101(7):557-65. [Medline].
Hahn IH, Lewin N. Chapter 115: Arthropods. In: Flomenbaum NE, Goldfrank LR, Hoffman RS, Howland MA, Lewin NA, Nelson LS, eds. Goldfrank's Toxicologic Emergencies. 8th ed. New York, NY: McGraw-Hill; 2006.
Isbister GK. Failure of intramuscular antivenom in Red-back spider envenoming. Emerg Med (Fremantle). Dec 2002;14(4):436-9. [Medline].
Isbister GK, Sibbritt D. Developing a decision tree algorithm for the diagnosis of suspected spider bites. Emerg Med Australas. Apr 2004;16(2):161-6. [Medline].
Further Reading
Keywords
spider bite, redback spider, spider envenomation, Jockey spider, latrodectism, latrotoxin, aLTX, neurotoxin, redback spider bite, spider bite treatment
