Seminar Spider bite Geoff rey K Isbister, Hui Wen Fan Spiders are a source of intrigue and fear, and several myths exist about their medical eff ects. Many people believe that Published Online bites from various spider species cause necrotic ulceration, despite evidence that most suspected cases of necrotic July 14, 2011 arachnidism are caused by something other than a spider bite. Latrodectism and loxoscelism are the most important DOI:10.1016/S0140- 6736(10)62230-1 clinical syndromes resulting from spider bite. Latrodectism results from bites by widow spiders (Latrodectus spp) and Discipline of Clinical causes local, regional, or generalised pain associated with non-specifi c symptoms and autonomic eff ects. Loxoscelism Pharmacology, University of is caused by Loxosceles spp, and the cutaneous form manifests as pain and erythema that can develop into a necrotic Newcastle, Newcastle, NSW, ulcer. Systemic loxoscelism is characterised by intravascular haemolysis and renal failure on occasion. Other important Australia (G K Isbister MD); spiders include the Australian funnel-web spider (Atrax spp and Hadronyche spp) and the armed spider (Phoneutria spp) Department of Clinical Toxicology and Pharmacology, from Brazil. Antivenoms are an important treatment for spider envenomation but have been less successful than Calvary Mater Newcastle, have those for snake envenomation, with concerns about their eff ectiveness for both latrodectism and loxoscelism. Newcastle, NSW, Australia (G K Isbister); and Centro de population, which is suffi cient for the routine Desenvolvimento Cultural, Introduction Instituto Butantan, São Paulo, 14 Spiders have been a source of intrigue and fear by human management of spider bite but not for research. Brazil (H W Fan PhD) beings for centuries, and numerous myths exist about Laboratory diagnosis is rarely available in clinical settings, Correspondence to: the medical eff ects of spiders.1 The predominant myth of and identifi cation of spider venom in human tissue has Dr Geoff rey K Isbister, c/o Calvary the past few decades has been that bites from various only been achieved in the research setting with Mater Newcastle, Edith St, species cause necrotic ulceration. Although this is partly Loxosceles spp15,16 and Phoneutria nigriventer.17 Waratah, NSW 2298, Australia geoff [email protected] true because bites by spiders from the genus Loxosceles The best prevention for spider bite is reduced contact can result in necrotic arachnidism and occasionally between human beings and medically dangerous spiders. systemic illness, most suspected cases of necrotic This can include chemical control of spiders in human arachnidism are not based on scientifi c evidence. habitations, and success varies for diff erent spiders. Despite there being more than 41 000 recorded species Pyrethroid pesticides are toxic to Loxosceles intermedia.18 of spider in the order Araneae,2 very few are medically Chemical repellents have been manufactured in some important. In one study from Australia,3 which described countries for loxoscelism prevention, but do not seem to the clinical eff ects in 750 defi nite cases of spider bite be eff ective.19 covering 26 spider families, most spiders caused only minor eff ects. Worldwide there are two medically Treatment important clinical syndromes resulting from spider bite: Antivenoms are a major therapeutic intervention for latrodectism (caused by Latrodectus spp) and loxoscelism envenomation syndromes, and antivenoms exist for (caused by Loxosceles spp).4,5 All other medically important many spider groups.20 However, antivenoms have been spiders are confi ned to regions within single continents less successful in the treatment of arachnidism than have or countries, such as the Australian funnel-web spider those for snake or scorpion envenomation. The use of (Atrax and Hadronyche spp)6 and the armed or wandering antivenom is based on clinical experience, which has led spider (Phoneutria spp) from Brazil.7,8 Spider venoms to discrepancies in the proportion of patients treated. For have become a source of interest in the past few decades. example, in Brazil, antivenom is rarely used to treat Several small peptides have been identifi ed that interact Phoneutria envenomation despite substantial and with diff erent ion channels, including sodium, potassium, distressing eff ects but is used widely to treat Loxosceles and acid-sensing channels.9–13 envenomation, although it is theoretically unlikely to be eff ective. Only two randomised controlled trials and a Epidemiology, diagnosis, and prevention phase 2 study of Latrodectus antivenom have been done, The epidemiology of spider bite depends on the interaction between spider and human beings, spider ecology, and the environment. The distribution of Search strategy and selection criteria medically important spiders is the most important factor We searched Medline from January, 1966, to July, 2010; in identifi cation of where clinically important arach- LILACS from January, 1982, to July, 2010; and Embase from nidism occurs throughout the world and is discussed for January, 1980, to July, 2010, with the terms “arachnidism each of the spider groups. NOT scorpion”, “latrodectism”, “loxosceles”, “phoneutria”, The diagnosis of spider bite is usually clinical, and and “spider envenoming”. We included further articles from defi nite bites should be based on a clear history of a reference lists, review articles, and major textbook chapters spider biting the person and then being identifi ed. on spider toxinology. Previous systematic reviews for Identifi cation is best done by collection of the spider and randomised controlled trials of spider bite treatment were expert identifi cation. However, some spiders such as included and updated. widow spiders can usually be identifi ed by the general www.thelancet.com Published online July 14, 2011 DOI:10.1016/S0140-6736(10)62230-1 1 Seminar pain syndrome in Australasia21,29 to a more systemic A B illness with the European widow spider, for which myocardial eff ects are reported.31 Only one study32 has compared diff erent species in the same geographical region in South Africa and showed a diff erence between Latrodectus indistinctus and Latrodectus geometricus. The table provides a comparison of the clinical eff ects for six diff erent Latrodectus spp for which suffi ciently large case series have been published.29,31–35 Pain is an almost universal feature of latrodectism and Figure 1: Latrodectus or widow spiders (A) Female Latrodectus hesperus or black widow spider from North America (photograph by Rick Vetter). (B) Female can be local bite-site pain, regional or radiating pain, or Latrodectus hasselti or redback spider from Australia (photograph by Geoff Isbister). back, chest, or abdominal pain. The onset of pain is usually gradual and can continue for hours to days. In and the results provided contradictory evidence.21–23 Australia, local pain radiating up the bitten limb or from Although Loxosceles antivenom is used in South America the bite site is typical,21,29 whereas in North and and is effi cacious in vitro,24,25 the delay in clinical South America back and abdominal pain predominate.33,35 presentation and the irreversible nature of cutaneous Diaphoresis is another characteristic feature of necrosis means that this laboratory fi nding might not latrodectism and often occurs in unusual patterns that translate into eff ective treatment.14,20,26 By contrast, are almost pathognomonic of latrodectism—diaphoresis antivenom for funnel-web spider envenomation is highly localised to the bite site, bilateral below-knee diaphoresis, eff ective and potentially life-saving because it can be and asymmetrical regional diaphoresis are some given early and reverse neurotoxic eff ects.6,20 characteristic patterns. Systemic envenomation occurs in about a third of Medically important spider bite and clinical cases, although the systemic features and the frequency syndromes vary for diff erent species. Non-specifi c symptoms such as Latrodectus spp (widow spiders) nausea, vomiting, headache, and fatigue are reported for Latrodectism results from bites by widow spiders most species. Muscle fasciculation and patchy localised (Latrodectus spp), which have a worldwide distribution paralysis can occur. Myocardial injury has been reported, and continue to migrate between continents. There are but only from some species of widow spiders such as 30 recognised species present throughout the Americas, Latrodectus tredecimguttatus, and has resulted in Africa, Europe, Asia, and Australasia.27 Latrodectus spp fatalities.31,36,37 Priapism is another unusual clinical eff ect are medium-size spiders and generally shiny black in reported for most Latrodectus species.38–41 colour with ventral red hourglass markings (fi gure 1A). The diagnosis of latrodectism is clinical and relies on However, the body colour and markings vary greatly, a history of spider bite resulting in clinical eff ects that such as the red back of Latrodectus hasselti (fi gure 1B), are consistent with latrodectism, which can vary for and the male spiders are much smaller than female diff erent Latrodectus species. Laboratory investigations spiders.4,28 Most medically important bites are from the are rarely needed, and no analytical assay exists to larger female spiders, but bites by male spiders have detect widow spider venoms in blood, urine, or at the been reported in Australia.29 bite site. Cardiac markers have been suggested if cardiac Much work has been done into toxins contained in involvement is suspected.