Editing Redback spider (section)

==Bites to humans==

===Incidence===
The redback spider has been historically responsible for more envenomations requiring antivenom than any other creature in Australia. However, by 2017 the spider was blamed for only 250 envenomations requiring antivenom annually.{{sfn|White|2013|p=203}}<ref>{{Cite journal|date=8 August 2017|title=Redback Spider Envenomation: Background, Pathophysiology, Epidemiology|url=https://emedicine.medscape.com/article/772484-overview#a6|website=emedicine.medscape.com|access-date=22 October 2017|archive-date=23 October 2017|archive-url=https://web.archive.org/web/20171023064046/https://emedicine.medscape.com/article/772484-overview#a6|url-status=live}}</ref> Estimates of the number of people thought to be bitten by redback spiders each year across Australia range from 2,000 to 10,000.<ref name=Nicholson2003/><ref name=White1998/> The larger female spider is responsible for almost all cases of redback spider bites. The smaller male was thought to be unable to envenomate a human, although some cases have been reported; their rarity is probably due to the male's smaller size and proportionally smaller fangs, rather than its being incapable of biting or lacking potent venom.<ref name="isbister"/><!--cites 13sentences--> The bite from both juvenile and mature females appears to have similar potency. The male bite usually only produces short-lived, mild pain.<ref name="isbister"/><!--cites 2 sentences--> Most bites occur in the warmer months between December and April, in the afternoon or evening.<ref name="isbister">{{cite journal|last=Isbister|first=Geoffrey K.|author2=Gray, Michael R.|title=Latrodectism: a Prospective Cohort Study of Bites by Formally Identified Redback Spiders|journal=Medical Journal of Australia|volume=179|issue=2|pages=88–91|year=2003|pmid=12864719|url=https://www.mja.com.au/journal/2003/179/2/latrodectism-prospective-cohort-study-bites-formally-identified-redback-spiders|type=Prospective cohort study|doi=10.5694/j.1326-5377.2003.tb05442.x|s2cid=25632248|access-date=3 September 2013|archive-date=21 September 2013|archive-url=https://web.archive.org/web/20130921060129/https://www.mja.com.au/journal/2003/179/2/latrodectism-prospective-cohort-study-bites-formally-identified-redback-spiders|url-status=live|url-access=subscription}}</ref><!--cites 1 sentences--><ref name="sutherland">{{cite journal |author1=Sutherland, S. |author2=Trinca, J. |title=Survey of 2144 Cases of Redback Spider Bites: Australia and New Zealand, 1963–1976 |journal=Medical Journal of Australia |volume=2 |issue=14 |pages=620–23 |year=1978 |pmid=732670 |type=Case report |doi=10.5694/j.1326-5377.1978.tb131783.x |s2cid=22729861 }}</ref> As the female redback is slow-moving and rarely leaves her web, bites generally occur as a result of placing a hand or other body part too close to the spider, such as when reaching into dark holes or wall cavities. Bites often also occur when a hidden spider is disturbed in items such as clothes, shoes, gloves, building materials, garden tools or children's outdoor toys.{{sfn|Sutherland|Tibballs|2001|p=393}}<ref name=Ibister2004/>

A 2004 review reported 46% of bites occurring on [[Anatomical terms of location#Proximal and distal|distal]] extremities of the limbs, 25% on [[Anatomical terms of location#Proximal and distal|proximal areas of limbs]] (upper arms and thighs), 21% on the trunk, and 7% on the head or neck.<ref name=Ibister2004/> In some cases the same spider bites a victim multiple times.<ref>{{cite news |url=http://nla.gov.au/nla.news-article122074552 |title=Spider Bite Proves Fatal. |newspaper=[[Queensland Times]] |location=Ipswich (Qld.) |date=26 February 1940 |page=6 Edition: Daily |publisher=National Library of Australia |access-date=5 September 2013 |archive-date=19 October 2021 |archive-url=https://web.archive.org/web/20211019062748/https://trove.nla.gov.au/newspaper/article/122074552 |url-status=live }}</ref><ref>{{cite news |url=http://nla.gov.au/nla.news-article98108718 |title=General News. Bitten by Redback Spider |newspaper=Western Star and Roma Advertiser |location=Toowoomba, Qld. |date=25 March 1936 |page=2 |publisher=National Library of Australia |access-date=5 September 2013 |archive-date=19 October 2021 |archive-url=https://web.archive.org/web/20211019062749/https://trove.nla.gov.au/newspaper/article/98108718 |url-status=live }}</ref> Historically, victims were often bitten on the genitalia, though this phenomenon disappeared as [[outhouse]]s were superseded by plumbed indoor toilets.<ref name="jelinek1997" /><ref>{{cite news|last=McIlraith|first=Shaun|title=Redbacks Giving Way to Progress|url=https://news.google.com/newspapers?id=RgMRAAAAIBAJ&dq=redback%20shoes%20spider&pg=2821%2C446841|newspaper=[[Sydney Morning Herald]]|date=4 January 1979|page=3|access-date=27 August 2020|archive-date=19 October 2021|archive-url=https://web.archive.org/web/20211019062747/https://news.google.com/newspapers?id=RgMRAAAAIBAJ&dq=redback+shoes+spider&pg=2821%2C446841|url-status=live}}</ref> Conversely, bites on the head and neck have increased with use of safety helmets and ear muffs.{{sfn|Sutherland|Tibballs|2001|p = 393}} Precautions to avoid being bitten include wearing gloves and shoes while gardening, not leaving clothes on the floor, and shaking out gloves or shoes before putting them on. Also, children can be educated not to touch spiders.<!-- refs for two sentences in this paragraph --><ref>{{cite web|url=https://australian.museum/learn/animals/spiders/spiders-in-the-house-and-garden/|title=Spiders in the House and Garden|author=Australian Museum|date=6 May 2013|work=Nature Culture Discover|publisher=Australian Museum|access-date=25 October 2013|location=Sydney, New South Wales|archive-date=6 July 2020|archive-url=https://web.archive.org/web/20200706174623/https://australian.museum/learn/animals/spiders/spiders-in-the-house-and-garden/|url-status=live}}</ref><ref>{{cite web|url=http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Spiders|title=Spiders|author=Department of Health|date=10 September 2013|work=Better Health Channel|publisher=State Government of Victoria|access-date=25 October 2013|url-status=dead|archive-url=https://web.archive.org/web/20131029203227/http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Spiders|archive-date=29 October 2013}}</ref>

===Venom===
{{Main|Latrotoxin}}
[[File:Latrodectus hasselti -Sydney, Australia-8.jpg|thumb|right|The distinctive red stripe of the adult female]]
The redback and its relatives in the genus ''Latrodectus'' are considered dangerous, alongside funnel-web spiders (''[[Atrax]]'' and ''[[Hadronyche]]''), mouse spiders (''[[Missulena]]''), wandering spiders (''[[Phoneutria]]'') and recluse spiders (''[[Loxosceles]]'').<ref name="Amo-Redback1">{{cite web | author=Australian Museum | title=Spider Facts | url=https://australian.museum/learn/animals/spiders/spider-facts/ | access-date=20 September 2013 | date=6 May 2013 | archive-date=13 July 2020 | archive-url=https://web.archive.org/web/20200713060040/https://australian.museum/learn/animals/spiders/spider-facts/ | url-status=live }}</ref><ref>{{cite journal|last=Espino-Solis|first=G.P.|author2=Riaño-Umbarila, L. |author3=Becerril, B. |author4= Possani, L.D. |title=Antidotes against Venomous Animals: State of the Art and Prospectives|journal=Journal of Proteomics|date=6 March 2009|volume=72|issue=2|pages=183–99|doi=10.1016/j.jprot.2009.01.020|pmid=19457345|type=Review}}</ref> Venom is produced by [[holocrine]] glands in the spider's [[chelicerae]] (mouth parts).<ref name=Rohou2007>{{cite journal |title=Insecticidal Toxins from Black Widow Spider Venom |date=15 March 2007|journal=Toxicon |volume=49 |pages=531–49 |first1= A |last1=Rohou |first2= J |last2=Nield |first3= Y.A. |last3=Ushkaryov|pmc=2517654 |issue=4–5 |doi=10.1016/j.toxicon.2006.11.021|pmid=17210168 |bibcode=2007Txcn...49..531R |type=Review }}</ref> Venom accumulates in the lumen of the glands and passes through paired ducts into the spider's two hollow fangs.<ref name=Rohou2007/><ref name="NicholsonGraudins"/> The venom of the redback spider is thought to be similar to that of the other ''Latrodectus'' spiders. It contains a complex mixture of cellular constituents, [[enzyme]]s and a number of high-molecular-weight toxins, including insect toxins and a vertebrate [[neurotoxin]] called [[alpha-latrotoxin]], which causes intense pain in humans.<ref name=Rohou2007/><ref name="NicholsonGraudins">{{cite journal|last1=Nicholson|first1=Graham M.|last2=Graudins|first2=Andis|title=Spiders of Medical Importance in the Asia-Pacific: Atracotoxin, Latrotoxin and Related Spider Neurotoxins|journal=Clinical and Experimental Pharmacology and Physiology|volume=29|issue=9|year=2002|pages=785–94|issn=0305-1870|pmid= 12165044| doi=10.1046/j.1440-1681.2002.03741.x|s2cid=12620544|type=Review}}</ref>

In [[vertebrates]], alpha-latrotoxin produces its effect through destabilisation of [[cell membrane]]s and [[degranulation]] of [[nerve|nerve terminals]], resulting in excessive release of [[neurotransmitter]]s, namely [[acetylcholine]], [[norepinephrine]] and [[Gamma-aminobutyric acid|GABA]]. Excess neurotransmitter activity leads to clinical manifestations of envenomation,<ref name="White">{{cite book | editor1 = Meier, J. | editor2 = White, J. | title = Handbook of Clinical Toxicology of Animal Venoms and Poisons | year = 1995 | publisher = CRC Press | url = http://www.toxinology.com/fusebox.cfm?staticaction=generic_static_files/toxdept_crcbook.html | isbn = 0-8493-4489-1 | access-date = 19 October 2021 | archive-date = 12 June 2018 | archive-url = https://web.archive.org/web/20180612141017/http://www.toxinology.com/fusebox.cfm?staticaction=generic_static_files%2Ftoxdept_crcbook.html | url-status = live }}</ref> although the precise mechanisms are not well understood.<ref name=Nimorakiotakis/> Acetylcholine release accounts for neuromuscular manifestations, and norepinephrine release accounts for the cardiovascular manifestations.<ref>{{Cite web|url=http://accessmedicine.mhmedical.com.acs.hcn.com.au/content.aspx?bookid=1658&sectionid=109385845|title=MedicalDirector Login|website=accessmedicine.mhmedical.com.acs.hcn.com.au|access-date=23 October 2017|archive-date=19 October 2021|archive-url=https://web.archive.org/web/20211019062752/https://acs.hcn.com.au/ksLicensing/auth0/institution?redirectURL=http%3A%2F%2Faccessmedicine.mhmedical.com.acs.hcn.com.au%2Fcontent.aspx%3Fbookid%3D1658%26sectionid%3D109385845|url-status=live}}</ref> Female redbacks have an average of around 0.08–0.10&nbsp;mg of venom, and experiments indicate that the [[median lethal dose]] (LD<sub>50</sub>) for mice at room temperature is 10–20% of this quantity (0.27–0.91&nbsp;mg/kg based on the mass of the mice used), but that it is considerably deadlier for mice kept at lower or higher temperatures.<ref name=Wiener1956Temperature>{{cite journal|last=Wiener|first=Saul|title=The Australian Red Back Spider (''Latrodectus Hasseltii''): II. Effect of Temperature on the Toxicity of Venom|journal=The Medical Journal of Australia|date=1 September 1956|volume=43|issue=9|pages=331–34|doi=10.5694/j.1326-5377.1956.tb56713.x|pmid=13368800|s2cid=44645205}}</ref> Pure alpha-latrotoxin has an LD<sub>50</sub> in mice of 20–40&nbsp;μg/kg.<ref>{{cite web|last=Rubin|first=Rebecca L.|title=Redback Spider Envenomation|url=http://emedicine.medscape.com/article/772484-overview#showall|work=Medscape Reference|publisher=WebMD LLC|access-date=16 October 2013|author2=Wiener, Sage W.|date=16 April 2012|archive-date=16 October 2013|archive-url=https://web.archive.org/web/20131016115138/http://emedicine.medscape.com/article/772484-overview#showall|url-status=live}}</ref>

The specific variant of the vertebrate toxin found in the redback was cloned and sequenced in 2012, and was found to be a sequence of 1180 [[amino acid]]s,<ref name=graudins2012>{{cite journal|last=Graudins|first=Andis|author2=Little, Michelle J. |author3=Pineda, Sandy S. |author4=Hains, Peter G. |author5=King, Glenn F. |author6=Broady, Kevin W. |author7= Nicholson, Graham M. |title=Cloning and Activity of a Novel α-latrotoxin from Red-back Spider Venom|journal=Biochemical Pharmacology|date=1 January 2012|volume=83|issue=1|pages=170–83|doi=10.1016/j.bcp.2011.09.024|pmid=22001442|type=Comparative study|hdl=10453/18571|hdl-access=free}}</ref> with a strong similarity to the equivalent molecule across the ''Latrodectus mactans'' clade.<ref>{{cite journal|last=Garb|first=J. E.|author2=Hayashi, C. Y. |title=Molecular Evolution of α-Latrotoxin, the Exceptionally Potent Vertebrate Neurotoxin in Black Widow Spider Venom|journal=Molecular Biology and Evolution|date=21 January 2013|volume=30|issue=5|pages=999–1014|doi=10.1093/molbev/mst011|pmid=23339183|pmc=3670729}}</ref> The syndromes caused by bites from any spiders of the genus ''Latrodectus'' have similarities;<ref>{{cite journal|last=Maretić|first=Zvonimir|year=1983|title=Latrodectism: Variations in Clinical Manifestations Provoked by ''Latrodectus'' Species of Spiders |journal=Toxicon|volume=21|issue=4|pages=457–66|doi=10.1016/0041-0101(83)90123-X|pmid=6353667|bibcode=1983Txcn...21..457M |type=Review}}</ref> there is some evidence there is a higher incidence of sweating, and local and radiating pain with the redback, while black widow envenomation results in more back and abdominal pain,<ref name="jelinek1997">{{cite journal|last=Jelinek|first=George A. |title=Widow Spider Envenomation (Latrodectism): a Worldwide Problem|journal=Wilderness & Environmental Medicine|year=1997 |volume=8|issue=4|pages=226–31|pmid=11990169|doi=10.1580/1080-6032(1997)008[0226:WSELAW]2.3.CO;2|type=Review|doi-access=free}}</ref> and abdominal rigidity is a feature common with bites from the west coast button spider (''[[Button spider|Latrodectus indistinctus]]'') of South Africa.<ref name="lancet"/>

One crustacean-specific and two insect-specific neurotoxins have been recovered from the [[Mediterranean black widow]] (''L. tredecimguttatus''), as have small [[peptide]]s that inhibit [[Angiotensin-converting enzyme|angiotensin-1-converting enzyme]];{{efn|These likely make the venom stronger by altering the victim's physiology.<ref name="vassilevski">{{cite journal|author1=Vassilevski, A. A.|author2=Kozlov, S. A.|author3=Grishin, E. V.|year=2009|title=Molecular Diversity of Spider Venom|journal=Biochemistry (Moscow)|volume=74|issue=13|pages=1505–34|url=http://protein.bio.msu.ru/biokhimiya/contents/v74/pdf/bcm_1505.pdf|doi=10.1134/S0006297909130069|pmid=20210706|s2cid=24572908|access-date=17 November 2013|archive-date=28 September 2010|archive-url=https://web.archive.org/web/20100928080451/http://protein.bio.msu.ru/biokhimiya/contents/v74/pdf/bcm_1505.pdf|url-status=live}}</ref> Angiotensin-converting-enzyme inhibitors, or [[ACE inhibitor]]s, are a class of widely-prescribed medications used in [[hypertension]] and [[heart failure]].<ref>{{cite journal|last=Sweitzer|first= Nancy K. |year=2003|title=What Is an Angiotensin Converting Enzyme Inhibitor?|journal=Circulation|volume=108|pages=e16–18|doi=10.1161/01.CIR.0000075957.16003.07|pmid= 12876137 |issue=3|doi-access=free}}</ref>

}} the venom of the redback, although little-studied, likely has similar agents.<ref name=graudins2012/>{{sfn|Sutherland|Tibballs|2001|p=390}}

===Antivenom===
[[File:F ab2 pFc.png|thumb|An [[antibody]] digested by [[pepsin]] yields two fragments: a [[F(ab')2|F(ab')<sub>2</sub>]] fragment and a pFc' fragment. Redback spider [[antivenom]] contains purified F(ab')<sub>2</sub> derived from [[IgG]] in hyperimmune horse [[Plasma (blood)|plasma]].<ref name=cmg2007>{{cite web|url=http://www0.health.nsw.gov.au/archive/policies/gl/2007/pdf/GL2007_006.pdf |title=Snakebite & Spiderbite Clinical Management Guidelines 2007 – NSW |publisher=Department of Health, NSW |page=47 |date=17 May 2007 |access-date=10 November 2013}}</ref><!--ref for last sentence only-->]]
{{Further|Antivenom}}
Redback antivenom was developed by [[CSL Limited|Commonwealth Serum Laboratories]], then a government body involved with discovering antivenoms for many venomous Australian creatures. Production involves the milking of venom from redbacks and repeatedly inoculating horses with non-lethal doses. The horse [[immune system]]s makes polyclonal [[antibody|antibodies]].<ref>{{cite web|url=http://www.powerhousemuseum.com/australia_innovates/?behaviour=view_article&Section_id=1030&article_id=10026|title=CSL antivenoms|author=ATSE project team|year=2001|work=Australia Innovates|publisher=Powerhouse Museum|access-date=9 October 2013|location=Haymarket, New South Wales|archive-date=7 August 2016|archive-url=https://web.archive.org/web/20160807152107/http://www.powerhousemuseum.com/australia_innovates/?behaviour=view_article&Section_id=1030&article_id=10026|url-status=live}}</ref> [[Blood plasma]], containing the antibodies, is extracted by [[plasmapheresis]].<ref>{{cite web|url=http://www.aomevents.com/media/files/AIMS%20NZIMLS%20SPC/Prowse.pdf |title=Antivenom Improvements |first=Claire |last=Prowse |publisher=aomevents.com |archive-url=https://web.archive.org/web/20131110170051/http://www.aomevents.com/media/files/AIMS%20NZIMLS%20SPC/Prowse.pdf|archive-date=10 November 2013 |access-date=10 November 2013}}</ref> The plasma is treated with [[pepsin]], and the active [[F(ab')2|F(ab')<sub>2</sub>]] fragments are separated and purified.<ref>{{cite book|url=https://books.google.com/books?id=BfdighlyGiwC&q=antivenom+redback+spider+pepsin&pg=PA262 |title=Medical Toxicology |author= Seifert, Stephen A |editor=Dart, Richard C|publisher=Lippincott Williams & Wilkins |edition=3rd |page=262 |year=2004|isbn=978-0-7817-2845-4}}</ref> Each vial contains 500 units of redback antivenom in approximately 1.5 ml,<ref name=ACCCN2011>{{cite book|author1=Elliott, Doug |author2=Aitken, Leanne |author3=Chaboyer, Wendy |title=ACCCN's Critical Care Nursing|publisher=Elsevier Australia|location=Chatswood, New South Wales|year=2011|edition=2nd|page=607|isbn=978-0-7295-4068-1|url=https://books.google.com/books?id=8Yg1lsItNdYC&q=redback+spider+ampoule&pg=PA607}}</ref> which is enough to inactivate 5&nbsp;mg of redback spider venom in a test tube.{{sfn|White|2013|p=312}} The antivenom has been safely administered to women in various stages of pregnancy.<ref name=ACCCN2011/> Redback antivenom has been widely used in Australia since 1956, although evidence from [[Scientific control|controlled]] studies for its [[effectiveness]] has been lacking. Recent trials show antivenom has a low response rate little better than placebo, and any effect is less than might be achieved with optimal use of standard analgesics.<ref name=":2" /><ref name=":3" /><ref name=":1" /> Further studies are needed to confirm or refute its effectiveness.<ref name="lancet" /> It appears clinically active against [[arachnidism]] caused by ''Steatoda'' spiders;<ref name="Nicholson2003" /><ref>{{cite journal|last=South|first=Mike|author2=Wirth, Peter|author3=Winkel, Ken D.|title=Redback Spider Antivenom used to Treat Envenomation by a Juvenile ''Steatoda'' Spider|journal=Medical Journal of Australia|date=December 1998|volume=169|issue=11|page=642|url=https://www.mja.com.au/journal/1998/169/11/redback-spider-antivenom-used-treat-envenomation-juvenile-steatoda-spider|pmid=9887917|type=Case report, letter|doi=10.5694/j.1326-5377.1998.tb123445.x|s2cid=33602865|access-date=5 September 2013|archive-date=21 September 2013|archive-url=https://web.archive.org/web/20130921060117/https://www.mja.com.au/journal/1998/169/11/redback-spider-antivenom-used-treat-envenomation-juvenile-steatoda-spider|url-status=live|url-access=subscription}}</ref><ref>{{cite journal|last=Graudins|first=Andis|author2=Gunja, Narendra |author3=Broady, Kevin W. |author4= Nicholson, Graham M. |title=Clinical and ''in vitro'' Evidence for the Efficacy of Australian Red-back Spider (''Latrodectus hasselti'') Antivenom in the Treatment of Envenomation by a Cupboard Spider (''Steatoda grossa'')|journal=Toxicon|date=June 2002|volume=40|issue=6|pages=767–75|doi=10.1016/S0041-0101(01)00280-X|pmid=12175614|bibcode=2002Txcn...40..767G |type=Case report}}</ref><ref>{{cite journal|last1=Atakuziev|first1=Bakhadir U.|last2=Wright|first2=Christine E.|last3=Graudins|first3=Andis|last4=Nicholson|first4=Graham M.|last5=Winkel|first5=Kenneth D.|title=Efficacy of Australian red-back spider (Latrodectus hasselti) antivenom in the treatment of clinical envenomation by the cupboard spider Steatoda capensis (Theridiidae)|journal=Toxicon|volume=86|pages=68–78|doi=10.1016/j.toxicon.2014.04.011|pmid=24853919|year=2014|bibcode=2014Txcn...86...68A }}</ref> however, as these cases are often mild and the evidence of its effectiveness is limited, this treatment is not recommended.<ref name="lancet" /> Similarly, the antivenom has been reported as effective with bites of ''L. katipo'', and ''L. tredecimguttatus''.<ref name="Nicholson2003">{{cite journal|last=Nicholson|first=Graham M.|author2=Graudins, Andis|title=Antivenoms for the Treatment of Spider Envenomation|journal=Toxin Reviews|date=1 January 2003|volume=22|issue=1|pages=35–59|doi=10.1081/TXR-120019019|hdl=10453/4596|s2cid=84894614|hdl-access=free}}</ref> Animal studies also support its use against envenomation from other widow spiders, having successfully been tested against venom from ''L. mactans'', ''[[Latrodectus hesperus|L. hesperus]]'', and ''[[Latrodectus tredecimguttatus|L. tredecimguttatus]]'' ([[Synonym (taxonomy)|synonym]] ''L.&nbsp;lugubris'').<ref name="Nicholson2003" /><ref>{{cite journal|last=Graudins|first=Andis|author2=Padula, Matthew |author3=Broady, Kevin |author4= Nicholson, Graham M. |title=Red-back Spider (''Latrodectus hasselti'') Antivenom Prevents the Toxicity of Widow Spider Venoms|journal=Annals of Emergency Medicine|date=February 2001|volume=37|issue=2|pages=154–60|doi=10.1067/mem.2001.113033|pmid=11174232}}</ref><ref>{{cite journal|last1=Daly |first1=Frank |last2=Hill |first2=Robert E. |last3=Bogdan |first3=Gregory M. |last4=Dart |first4=Richard C.|title=Neutralization of ''Latrodectus mactans'' and ''L. hesperus'' Venom by Redback Spider (''L. hasseltii'') antivenom|journal=Clinical Toxicology|date=1 January 2001|volume=39|issue=2|pages=119–23|doi=10.1081/CLT-100103826|pmid=11407496|last5=Dart|first5=Richard C.|s2cid=22286370 |type=Comparative study}}</ref>

===Signs and symptoms===
{{Main|Latrodectism}}
Envenomation from a redback spider bite produces a syndrome known as [[latrodectism]]. A small but significant percentage of people bitten develop significant pain or systemic symptoms.<ref name=isbister2006/> The diagnosis is made from the clinical condition, often based on the victim being aware of a bite and ideally with identification of the spider. Laboratory tests are rarely needed and there is no specific test for the venom or latrodectism.<ref name="lancet"/>

The redback's small size means that swelling or puncture marks at the bite site are uncommon. The bite may be painful from the start, but more often only feels like a pinprick or mild burning sensation.<ref name=Ibister2004/> Within an hour, a more severe local pain may develop with local sweating and sometimes [[piloerection]] (goosebumps)—these three symptoms together are a classic presentation of redback spider envenomation.{{sfn|White|2013|p=183}} Pain, swelling and redness can spread proximally up a limb or away from the bite site<ref name="Slaughter">{{cite journal|author1=Slaughter, R. J. |author2=Beasley, D. M. |author3=Lambie, B. S. |author4=Schep, L. J. |title=New Zealand's venomous creatures |journal=[[The New Zealand Medical Journal]] |volume=122 |issue=1290 |pages=83–97 |year=2009 |pmid=19319171 |url=http://www.nzma.org.nz/journal/122-1290/3494/ |url-status=dead |archive-url=https://web.archive.org/web/20110417090807/http://www.nzma.org.nz/journal/122-1290/3494/ |archive-date=17 April 2011 }}</ref><ref name=Ibister2004>{{cite journal|last=Isbister|first=Geoffrey K.|author2=White, Julian |title=Clinical Consequences of Spider Bites: Recent Advances in our Understanding|journal=Toxicon|date=April 2004|volume=43|issue=5|pages=477–92|doi=10.1016/j.toxicon.2004.02.002|pmid=15066408|bibcode=2004Txcn...43..477I |type=Review}}</ref><ref name="lancet"/><!--cites 2 sentences-->
and regional lymph nodes may become painful.<ref name="jelinek1997"/> Some subjects with delayed symptoms may present with a characteristic sweating and pain in the lower limbs,{{sfn|White|2013|p=183}} generally below the knees,<ref name="lancet"/> or a burning sensation in the soles of the feet. This may eventuate even if the person was bitten somewhere else on their body.{{sfn|White|2013|p=183}}<!-- cites previous 1.5 sentences -->

Around one in three subjects develops systemic symptoms;<ref name="lancet"/> after a number of hours, or rarely, delayed for more than 24 hours.<ref name="sutherland"/><ref name=jelinek1989>{{cite journal |author1=Jelinek, G. A. |author2=Banham, N. D. |author3=Dunjey, S. J. |title=Red-back Spider-bites at Fremantle Hospital, 1982–1987|journal=Medical Journal of Australia |volume=150 |issue=12 |pages=693–95 |year=1989 |pmid= 2733615|type=Case report|doi=10.5694/j.1326-5377.1989.tb136762.x |s2cid=204110952 }}</ref> Symptoms typically include nausea, vomiting, abdominal or chest pain, agitation, headache, generalised sweating and [[hypertension]].<ref name="lancet"/>{{sfn|White|2013|p=183}} Other non-specific systemic effects such as malaise and lethargy are also common. Rarely, other effects are reported such as neurological manifestations, fever and priapism (uncontrolled erection of the penis).<ref name=":2" /> Severe pain usually persists for over 24 hours after being bitten. Symptoms of envenomation may linger for weeks or even months.<ref name=Nimorakiotakis/> Rare complications include localised skin infection, seizure, coma, [[pulmonary oedema]], or [[respiratory failure]].<ref name="sutherland"/> Children, the elderly, or those with serious medical conditions are at much higher risk of severe effects resulting from a bite.<ref name="White"/> Infants have died within hours of a bite, but adult fatalities have taken up to 30 days.<ref name=MorningBulletin1954>{{cite news |url=http://nla.gov.au/nla.news-article57311162 |title=Nature Notes Red-backs and Black Widow |newspaper=[[The Morning Bulletin]] |location=Rockhampton, Queensland |date=2 March 1954 |page=6 |publisher=National Library of Australia |access-date=4 September 2013 |archive-date=19 October 2021 |archive-url=https://web.archive.org/web/20211019063040/https://trove.nla.gov.au/newspaper/article/57311162 |url-status=live }}</ref>

Children and infants may be unable to report being bitten, making it difficult to associate their symptoms with a spider bite.<ref name=isbister2006>{{cite journal|last=Isbister |first=Geoffrey K |year=2006 |title=Spider bite: a current approach to management |journal=Australian Prescriber |volume=29 |issue=6 |pages=156–58 |doi=10.18773/austprescr.2006.095 |doi-access=free }}</ref> Symptoms seen in infants include inconsolable crying, refusing to feed and a general [[erythema]]tous rash.{{sfn|White|2013|p=225}}{{efn|Published studies specifically looking at effects in children have been retrospective only and too limited to draw conclusive results.<ref name=Ibister2004/> A ten-year retrospective study of children bitten and admitted to hospital in Perth found that the clinical features resemble those of adult cases, and 21% required antivenom—a rate similar to adult use,<ref>{{cite journal|author1=Mead, H.J. |author2=Jelinek, G.A. |year=1993|title=Red-back Spider Bites to Perth Children, 1979–1988|journal=Journal of Paediatrics and Child Health|volume=29|issue=4|pages=305–08 |doi=10.1111/j.1440-1754.1993.tb00518.x|pmid=8373679 |s2cid=25640556 }}</ref> while a ten-year retrospective study from Alice Springs Hospital found that 83% required antivenom therapy, with irritability, hypertension and sweating as the most common clinical symptoms.<ref name=Trethewy2003>{{cite journal|author1=Trethewy, Christopher E. |author2=Bolisetty, Srinivas |author3=Wheaton, Gavin |year=2003|title=Red-back Spider Envenomation in Children in Central Australia|journal=Emergency Medicine|volume=15|issue=2|pages=170–75|doi=10.1046/j.1442-2026.2003.00435.x|pmid=12675627}}</ref>}} Muscle aches and pains, and neck spasm are often seen in children over four years of age.<ref name=Nimorakiotakis/>

Unlike those of some other spiders, redback bites do not [[necrosis|necrose]].<ref>{{cite journal|last=Young|first=Anna R.|author2=Pincus, Steven J. |title=Comparison of Enzymatic Activity from Three Species of Necrotising Arachnids in Australia: ''Loxosceles rufescens'', ''Badumna insignis'' and ''Lampona cylindrata''|journal=Toxicon|date=February–March 2001|volume=39|issue=2–3|pages=391–400|doi=10.1016/S0041-0101(00)00145-8|pmid=10978759|bibcode=2001Txcn...39..391Y |type=Comparative study}}</ref> <!-- Even envenomated bites do not cause miscarriage of pregnancies, and foetuses are typically unaffected.<ref>{{cite journal|last=Vetter|first=Richard S.|author2=Visscher, P. Kirk |title=Bites and Stings of Medically Important Venomous Arthropods|journal=International Journal of Dermatology|date=July 1998|volume=37|issue=7|pages=481–96|doi=10.1046/j.1365-4362.1998.00455.x|pmid=9679688}}</ref> --> Latrodectism has been misdiagnosed as various medical conditions including [[acute hepatitis]], [[sepsis]], [[testicular torsion]] or an [[acute abdomen]].<ref name=Nimorakiotakis/>

===Treatment===
Treatment is based on the severity of the envenomation. The majority of cases do not require medical care, and patients with localised pain, swelling and redness usually require only local application of ice and simple oral [[analgesia]] such as [[paracetamol]]. Pressure immobilisation of the wound site is not recommended. Keeping the victim still and calm is beneficial.<ref name="Slaughter"/><ref>{{cite web|url=http://www.ambulance.nsw.gov.au/Media/docs/funnel_web_and_redback_spider_bites-5d64cbaa-fbb8-439f-b281-0d0c4d380cbb-0.pdf|title=Funnel Web and Redback Spider Bites: First Aid Advice|author=New South Wales Ambulance Service|year=2008|work=Standard Operating Policy|publisher=State Government of New South Wales|access-date=13 October 2013|archive-date=6 March 2014|archive-url=https://web.archive.org/web/20140306160437/http://www.ambulance.nsw.gov.au/Media/docs/funnel_web_and_redback_spider_bites-5d64cbaa-fbb8-439f-b281-0d0c4d380cbb-0.pdf|url-status=live}}</ref>

Hospital assessment is recommended if simple pain relief does not resolve local pain, or systemic symptoms occur.{{sfn|White|2013|p=198}}<ref name="Murray">{{cite book | last = Murray | first = L. | author2 = Daly, F.| author3 = Little, M.| author4 = Cadogan, M.| title = Toxicology Handbook| publisher = Churchill Livingstone| location = Sydney | year = 2011 | pages = 470–79| isbn = 978-0-7295-3939-5}}</ref> [[Opioid]] analgesics may be necessary to relieve pain.<ref name="lancet"/> Antivenom has been historically given for adults suffering severe local pain or systemic symptoms consistent with latrodectism, which include pain and swelling spreading proximally from site, distressing local or systemic pain, chest pain, abdominal pain, or excessive sweating ([[diaphoresis]]).{{sfn|White|2013|pp=203–04}} A significant proportion of bites will not result in envenomation or any symptoms developing; around 2–20% of bite victims have been treated with antivenom.{{efn|The exact fraction of bites that require antivenom is difficult to quantify, because many bites are unreported. Figures from the manufacturer show that 344 cases required antivenom treatment in 1995,<ref name=White1998/> and in 2011 the figure was around 200.<ref name=Booth2008/> Estimates for the total number of bites range from 2,000<ref name=Nicholson2003/> to 10,000.<ref name=White1998/> These estimates correspond to a broad range of about 2–17%, and reports have generally expressed this as "around" or "under" 20%.<ref name=Nicholson2003/><ref name=White1998/> Two studies of redback victims who attended hospitals found that 6/23 (26%)<ref name="isbister"/> and 32/150 (21%)<ref name="jelinek1989"/> received antivenom.}}<ref name=White1998>{{cite journal |author=White, J. |title=Envenoming and Antivenom use in Australia |journal=Toxicon |volume=36 |issue=11 |pages=1483–92 |year=1998 |pmid=9792162 |doi=10.1016/S0041-0101(98)00138-X|bibcode=1998Txcn...36.1483W }}</ref> In an Australian study of 750 emergency hospital admissions for spider bites where the spider was definitively identified, 56 were from redbacks. Of these, 37 had significant pain lasting over 24 hours. Only six were treated with the antivenom.<ref name="bite study">{{Cite journal | last1 = Isbister | first1 = G. K. | last2 = Gray | first2 = M. R. | title = A Prospective Study of 750 Definite Spider Bites, with Expert Spider Identification | doi = 10.1093/qjmed/95.11.723 | journal = QJM | volume = 95 | issue = 11 | pages = 723–31 | year = 2002 | pmid =  12391384| doi-access = free }}</ref>

The antivenom manufacturer's product information recommends one vial, although more has been used.{{sfn|White|2013|p=312}} Past guidelines indicated two vials, with a further two vials recommended if symptoms did not resolve within two hours, however recent guidelines state "antivenom is sometimes given if there is a history, symptoms and signs consistent with systemic envenoming, and severe pain unresponsive to oral analgesics ... however recent trials show antivenom has a low response rate little better than placebo, and any effect is less than might be achieved with optimal use of standard analgesics."{{sfn|White|2013|pp=203–04}}<ref name=":2" /> The antivenom can be given by injection [[Intramuscular injection|intramuscularly]] (IM) or [[Intravenous therapy|intravenously]] (IV). The manufacturer recommends IM use, with IV administration reserved for life-threatening cases.<ref name="proinfo">{{cite web|url=http://www.csl.com.au/s1/cs/auhq/1196562765747/Web_Product_C/1196562644318/ProductDetail.htm|title=Redback Antivenom Product Information|year=2009|publisher=CSL Ltd|location=Melbourne, Australia|access-date=10 September 2013|archive-date=21 September 2013|archive-url=https://web.archive.org/web/20130921055927/http://www.csl.com.au/s1/cs/auhq/1196562765747/Web_Product_C/1196562644318/ProductDetail.htm|url-status=live}}</ref> In January 2008 toxicologist Geoffrey Isbister suggested IM antivenom was not as effective as IV antivenom,<ref name="isbister"/><ref>{{cite journal |doi=10.1046/j.1442-2026.2002.00356.x |author=Isbister, Geoff |title=Failure of Intramuscular Antivenom in Redback Spider Envenoming |journal=Emergency Medicine Australasia |volume=14 |issue=4 |pages=436–39 |year=2002 |pmid=12534488}}</ref> after proposing that IM antivenom took longer to reach the [[Serum (blood)|blood serum]].<ref name="serum study">{{Cite journal | last1 = Isbister | first1 = G. K. | last2 = O'Leary | first2 = M. | last3 = Miller | first3 = M. | last4 = Brown | first4 = S. G. A. | last5 = Ramasamy | first5 = S. | last6 = James | first6 = R. | last7 = Schneider | first7 = J. S. | doi = 10.1111/j.1365-2125.2007.03004.x | title = A comparison of serum antivenom concentrations after intravenous and intramuscular administration of redback (widow) spider antivenom | journal = British Journal of Clinical Pharmacology | volume = 65 | issue = 1 | pages = 139–43 | year = 2008 | pmid =  18171334| pmc =2291270 }}</ref> Isbister subsequently found the difference between IV and IM routes of administration was, at best, small and did not justify routinely choosing one route over the other.<ref>{{cite journal|vauthors=Isbister GK, Brown SG, Miller M, Tankel A, Macdonald E, Stokes B, Ellis R, Nagree Y, Wilkes GJ, James R, Short A|title=A randomised controlled trial of intramuscular vs. intravenous antivenom for latrodectism—the RAVE study|journal=QJM|year=2008|volume=101|issue=7|pages=557–65|doi=10.1093/qjmed/hcn048|pmid=18400776|doi-access=free}}</ref>

These concerns led two handbooks to recommend IV in preference to IM administration in Australian practice.{{sfn|White|2013|p=205}}<ref name="Murray"/>{{efn|A 2006 questionnaire found that of 218 Emergency physicians, 34 used the antivenom IM exclusively, 36 used IM then IV, 63 IV exclusively and 80 had no preference—that is, there was no consensus for preferred route.<ref>{{cite journal|author1=Brown, Simon A. |author2=Isbister, Geoffrey K. |year=2007|title=Route of administration of redback spider bite antivenom: Determining clinician beliefs to facilitate Bayesian analysis of a clinical trial|journal=Emergency Medicine Australasia |volume=19|issue=5|pages=458–63 |doi=10.1111/j.1742-6723.2007.01014.x|pmid=17919219|s2cid=310139 }}</ref>}} Despite a long history of usage and anecdotal evidence of effectiveness, there is a lack of data from controlled studies confirming the antivenom's benefits.<ref name="lancet"/> In 2014 Isbister and others conducted a randomized controlled trial of intravenous antivenom versus placebo for Redback envenomation, finding the addition of antivenom did not significantly improve pain or systemic effects, while antivenom resulted in acute hypersensitivity reactions in 3.6 per cent of those receiving it.<ref name=":3">{{cite journal |doi=10.1016/j.annemergmed.2014.06.006 |pmid=24999282 |title=Randomized Controlled Trial of Intravenous Antivenom Versus Placebo for Latrodectism: The Second Redback Antivenom Evaluation (RAVE-II) Study |journal=Annals of Emergency Medicine |volume=64 |issue=6 |pages=620–8.e2 |year=2014 |last1=Isbister |first1=Geoffrey K. |last2=Page |first2=Colin B. |last3=Buckley |first3=Nicholas A. |last4=Fatovich |first4=Daniel M. |last5=Pascu |first5=Ovidiu |last6=MacDonald |first6=Stephen P.J. |last7=Calver |first7=Leonie A. |last8=Brown |first8=Simon G.A. |hdl=2123/14928 |url=https://ses.library.usyd.edu.au/bitstream/2123/14928/1/Isbister_et_al_2014.pdf |hdl-access=free |access-date=24 September 2019 |archive-date=20 July 2018 |archive-url=https://web.archive.org/web/20180720071527/https://ses.library.usyd.edu.au/bitstream/2123/14928/1/Isbister_et_al_2014.pdf |url-status=live }}</ref> The question of abandoning the antivenom on the basis of this and previous studies came up in the Annals of Emergency Medicine in 2015 where White and Weinstein argued that if the recommendations in the 2014 Isbister et al. paper were followed it would lead to abandonment of antivenom as a treatment option, an outcome White and Weinstein considered undesirable. Authors of the 2014 Isbister et al. paper responded in the same issue by suggesting patients for whom antivenom is considered should be fully informed "there is considerable weight of evidence to suggest it is no better than placebo", and in light of a risk of anaphylaxis and serum sickness,  "routine use of the antivenom is therefore not recommended".<ref name=":1">{{cite journal |doi=10.1016/j.annemergmed.2014.08.022 |pmid=25529159 |title=Latrodectism and Effectiveness of Antivenom |journal=Annals of Emergency Medicine |volume=65 |issue=1 |pages=123–24 |year=2015 |last1=White |first1=Julian |last2=Weinstein |first2=Scott A. }}</ref>

Before the introduction of antivenom, [[benzodiazepine]]s and intravenous [[calcium gluconate]] were used to relieve symptoms of pain and distress,<ref name="rauber83" /><ref>{{cite journal|last=Braitberg|first=George|year=2009|title=Spider bites: Assessment and management|url=http://www.racgp.org.au/afp/200911/200911braithberg.pdf|journal=Australian Family Physician|type=Review|volume=38|issue=11|pages=862–67|pmid=19893831|access-date=29 October 2013|archive-date=1 November 2013|archive-url=https://web.archive.org/web/20131101170857/http://www.racgp.org.au/afp/200911/200911braithberg.pdf|url-status=live}}</ref> although calcium is not recommended as its benefit has not been shown in clinical trials.{{sfn|White|2013|p=206}}

Studies support the safety of antivenom, with around a 5% chance of an acute reaction, 1–2% of [[anaphylaxis]] and 10% chance of a delayed reaction due to [[serum sickness]].<ref name="lancet"/> Nevertheless, it is recommended that an injection of [[adrenaline]] be ready and available in case it is needed to treat a severe anaphylactic reaction,<ref name="proinfo"/> and also that the antivenom from the vial be administered diluted in a 100 ml bag of intravenous solution for infusion over 30 minutes.{{sfn|White|2013|p=209}} While it is rare that patients report symptoms of envenomation lasting weeks or months following a bite,<ref name="isbister"/> there are case reports from the 1990s in which antivenom was reported to be effective in the relief of chronic symptoms when administered weeks or months after a bite.<ref>{{cite journal |author1=Banham, N. |author2=Jelinek, G. |author3=Finch, P. |title=Late Treatment with Antivenom in Prolonged Redback Spider Envenomation |journal=Medical Journal of Australia |volume=161 |issue=6 |pages=379–81 |year=1994 |pmid=8090117|type=Case report|doi=10.5694/j.1326-5377.1994.tb127492.x |s2cid=27782875 }}</ref><ref name="Wells">{{cite journal |author1=Wells, C. L. |author2=Spring, W. J. |title=Delayed but Effective Treatment of Red-back Spider Envenomation|journal=Medical Journal of Australia |volume=164 |issue=7 |page=447 |year=1996 |pmid= 8609868|type=Case report, letter|doi=10.5694/j.1326-5377.1996.tb122109.x |s2cid=31114115 }}</ref> However, in the vast majority of cases, it is administered within 24 hours.<ref name="sutherland"/>

===Prognosis===
According to [[Ministry of Health (New South Wales)|NSW Health]], redback spider bites were considered not life-threatening but capable of causing severe pain and systemic symptoms that could continue for hours to days.<ref name=":2" /><ref name=":6">{{Cite web|url=http://www1.health.nsw.gov.au/pds/ActivePDSDocuments/GL2014_005.pdf|title=Snakebite and Spiderbite Clinical Management Guidelines 2013, Third Edition|date=16 March 2014|publisher=Ministry of Health, NSW|access-date=23 October 2017|archive-date=15 December 2017|archive-url=https://web.archive.org/web/20171215111714/http://www1.health.nsw.gov.au/pds/ActivePDSDocuments/GL2014_005.pdf|url-status=live}} [[File:CC-BY icon.svg|50x50px]] Material was copied from this source, which is available under a [[creativecommons:by/4.0/|Creative Commons Attribution 4.0 International License]].</ref> In almost all cases, symptoms resolve within a week.<ref name=isbister2006/> Fatalities are extremely unlikely.{{sfn|White|2013|p=181}} In 2016, the death of a [[hiking|bushwalker]] from a redback spider bite was widely reported. In this case, the death occurred from secondary infection; and the man in question had just recovered from a serious car accident.<ref name="Jayden">{{cite news |url=https://www.northernstar.com.au/news/mullum-man-jayden-burleigh-dies-days-after-redback/2994925/ |title=More than $12k donated to family of man killed by spider |newspaper=[[The Northern Star]] |date=3 April 2016 |access-date=13 August 2018 |archive-date=13 August 2018 |archive-url=https://web.archive.org/web/20180813143325/https://www.northernstar.com.au/news/mullum-man-jayden-burleigh-dies-days-after-redback/2994925/ |url-status=live }}</ref> Apart from that, there have been no deaths due to redback bite since the introduction of [[antivenom]].{{efn|No deaths since 1956 have been formally reported,<ref name="Wiener"/> but a spider expert at the [[CSIRO]] Division of Entomology told a news reporter that he had heard of one other death.<ref name=Warden1989/>}}<ref name="Wiener">{{cite journal |last=Wiener |first=Saul |title=Latrodectism: a Prospective Cohort Study of Bites by Formally Identified Redback Spiders |journal=Medical Journal of Australia |volume=179 |issue=8 |pages=455–56 |year=2003 |pmid=14558881 |url=http://www.mja.com.au/public/issues/179_08_201003/letters201003_fm-8.html |type=Comment, letter |doi=10.5694/j.1326-5377.2003.tb05640.x |s2cid=40170866 |access-date=13 February 2012 |archive-date=1 September 2011 |archive-url=https://web.archive.org/web/20110901081929/http://www.mja.com.au/public/issues/179_08_201003/letters201003_fm-8.html |url-status=live |url-access=subscription }}</ref> Before this, redback spider bites had been implicated in at least 14 deaths in Australia, however these cases cannot be definitively linked to the redback bite as the sole cause.<ref name=Booth2008>{{cite journal |author=Booth, Carol |title=Along Came A Spider |journal=Australian Geographic |date=July–September 2008 |url=http://www.australiangeographic.com.au/journal/along-came-a-spider.htm |access-date=25 March 2010 |archive-url=https://web.archive.org/web/20091006070407/http://www.australiangeographic.com.au/journal/along-came-a-spider.htm |archive-date=6 October 2009 |url-status=dead  }}</ref><ref name=avru>{{cite web|url=http://www.avru.org/compendium/biogs/A000006b.htm |work=The Australian Venom Compendium |author=Alafaci, Annette |title=Redback Spiders |publisher=Australian Venom Research Unit |date= 25 August 2007 |archive-url=https://web.archive.org/web/20150115112010/http://www.avru.org/compendium/biogs/A000006b.htm|archive-date=15 January 2015 |access-date=2 September 2013}}</ref>