Post by Doc on May 31, 2011 14:56:15 GMT -5
A spider bite is an injury resulting from the bites of spiders or other closely related arachnids.
Spiders are active hunters and strongly rely on their bites to paralyze and kill their prey before consuming it. Since spiders are aware of the effect caused by their bites, they also widely bite on self-defense any intruder risking to damage individuals or their webs (i.e. bites are their naturally occurring defense mechanism). While many spiders will never attack animals larger than themselves, preferring to either run away or feign death[citation needed], some share a rather aggressive behavior and will do so even if no real danger exists[citation needed].
Only a minority of spider species possess chelicera strong enough to penetrate human skin, however due to their strong surviving potential, they are those most frequently encountered in human habitats. About 98% of the bites inflicted by these species are harmless,[1] but some symptoms can include necrotic wounds, systemic toxicity and, in some cases, death. Only some two hundred species in twenty genera (out of over 40,000 known species) are known to have serious, potentially lethal bites.[2]
In most cases of bites, the chief concern is the spider's venom, although in some cases medically non-significant spiders can transmit infectious diseases. Spiders regarded as dangerous possess venom that is toxic to humans, in quantities that can be delivered by a single bite. Only three spider families are known to be non-venomous, i.e. lacking venom glands or any proper way to deliver it. They are Uloboridae, Holarchaeidae and Liphistiidae. These spiders, however, do possess fangs and can deliver sharp, unpleasant bites. In addition, the fangs of Liphistiidae can often inflict infections spread through the skin, mostly due to their large size, which in theory could represent more danger than the bite of a non-lethal venomous spider species.
Spider bites may be misdiagnosed by both the general public and medical practitioners. Many other conditions both infectious and non-infectious can be confused with spider bites.[3] Many of these conditions are far more common and more likely to be the source of necrotic wounds.[4]
Signs and symptoms
A Brazilian man 31 hours after having been bitten on his face by a Loxoceles spider.
4 month after a brown recluse spider bite with scar remainingPain from non venomous spider bites typically lasts for 5 to 60 minutes while pain from venomous spider bites frequently lasts for greater than 24 hours.[5] The rate of a bacterial infection due to a spider bite is low (0.9%).[5]
[edit] PathophysiologyA primary concern of the bite of a spider is the effect of its venom. A spider envenomation occurs whenever a spider injects venom into the skin. Not all spider bites involve injection of venom into the skin, and the amount of venom injected can vary based on the type of spider and the circumstances of the encounter. With very few exceptions, such as the so-called camel spider (which is not a true spider), the mechanical injury from a spider bite is not a serious concern for humans. Some spider bites do leave a large enough wound that infection may be a concern, and other species are known to consume prey which is already dead, which also may pose a risk for transmission of infectious bacteria from a bite.[6] However, it is generally the toxicity of spider venom which poses the most risk to human beings; several spiders are known to have venom which can be fatal to humans in the amounts that a spider will typically inject when biting.
All spiders are capable of producing venom, with the exception of the hackled orb-weavers, the Holarchaeidae, and the primitive Mesothelae[citation needed]. (Other arachnids often confused with spiders, such as the harvestman and sun spiders, also do not produce venom). Nonetheless, only a small percentage of species have bites which pose a danger to people. Many spiders do not have mouthparts capable of penetrating human skin. While venoms are by definition toxic substances, most spiders do not have venom which is sufficiently toxic (in the quantities delivered[citation needed]) to require medical attention and, of those that do, only a few are known to produce fatalities[citation needed].
Spider venoms work on one of two fundamental principles; they are either neurotoxic (attacking the nervous system) or necrotic (attacking tissues surrounding the bite, and in some cases, attacking vital organs and systems)[citation needed].
[edit] Neurotoxic venomThe majority of spiders with serious bites possess a neurotoxic venom of some sort, though the specific manner in which the nervous system is attacked varies from spider to spider.[7][8][9]
Widow spider venom contains components known as latrotoxins, which cause the release of the neurotransmitter acetylcholine, stimulating muscle contractions. This can affect the body in several ways, including causing painful abdominal cramps, as well as interfering with respiration, and causing other systemic effects.[2]
The venom of Australasian funnel-web spiders and mouse spiders works by opening sodium channels, causing excessive neural activity which interferes with normal bodily function.
The venom of Brazilian wandering spiders is also a potent neurotoxin, which attacks multiple types of ion channels [10] In addition, the venom contains high levels of serotonin, making an envenomation by this species particularly painful.
[edit] Necrotic venomSpiders known to have necrotic venom are found in the family Sicariidae, a family which includes both the recluse spiders and the six-eyed sand spiders. Spiders in this family possess a known dermonecrotic agent sphingomyelinase D,[11][12] which is otherwise found only in a few pathogenic bacteria.[13][14] Some species in this family are more venomous than others; according to one study, the venom of the chilean recluse and several species of six-eyed sand spider indigenous to southern Africa, contains an order of magnitude more of this substance than do other Sicariidae spiders such as the brown recluse.[15] Bites by spiders in this family can produce symptoms ranging from minor localized effects, to severe dermonecrotic lesions, up to and including severe systemic reactions including renal failure, and in some cases, death.[16] Even in the absence of systemic effects, serious bites from Sicariidae spiders may form a necrotising ulcer that destroys soft tissue and may take months and very rarely years to heal, leaving deep scars. The damaged tissue may become gangrenous and eventually slough away. Initially there may be no pain from a bite, but over time the wound may grow to as large as 10 inches (25 cm) in extreme cases. Bites usually become painful and itchy within 2 to 8 hours, pain and other local effects worsen 12 to 36 hours after the bite with the necrosis developing over the next few days.[17]
Serious systemic effects may occur before this time, as the venom spreads throughout the body in minutes. Mild symptoms include nausea, vomiting, fever, rashes, and muscle and joint pain. Rarely more severe symptoms occur including hemolysis, thrombocytopenia, and disseminated intravascular coagulation.[18] Debilitated patients, the elderly, and children may be more susceptible to systemic loxoscelism. Deaths have been reported for both the brown recluse and the related South American species L. laeta and L. intermedia.
Numerous other spiders have been associated with necrotic bites in the medical literature. Examples include the Hobo spider and the Yellow Sac spider. However, the bites from these spiders are not known to produce the severe symptoms that often follow from a recluse spider bite, and the level of danger posed by each has been called into question.[19][20] So far, no known necrotoxins have been isolated from the venom of any of these spiders, and some arachnologists have disputed the accuracy of many spider identifications carried out by bite victims, family members, medical responders, and other non-experts in arachnology. There have been several studies questioning danger posed by some of these spiders. In these studies, scientists examined case studies of bites in which the spider in question was positively identified by an expert, and found that the incidence of necrotic injury diminished significantly when "questionable" identifications were excluded from the sample set.[21][22]
[edit] Comparative analysisIt is often asked which type of spider is the most "dangerous" in the world. There isn't a simple answer to this question, as there are many things which must be taken into account when considering the amount of danger posed by spider bites:
Firstly, it is often the case that a spider bite is "dry" – the skin may be pierced, but little or no venom is injected into the victim. In such an instance, little or none of the spider's dangerous potential for harm is manifested.
Secondly, there have been reports of spider bites (by spiders considered otherwise harmless) causing allergic reactions in some individuals, up to and including anaphylactic shock, a life-threatening condition (much the same as a sting from an ant, bee, or wasp may produce a harmful effect apart from the toxic quality of its venom).[23]
Thirdly, many spiders listed as dangerous are seldom encountered, or have dispositions that make them unlikely to bite despite the high toxicity of their venom.
Finally, little is known about the toxicity of many spiders, due to their infrequent encounters with humans; the list of venomous spiders is limited to those that are linked to medical events in humans or who otherwise have been extensively studied.
It should also be noted that, for healthy adults, a bite by even the most toxic spiders on the list may require hours before death ensues; if timely appropriate emergency medical treatment is administered, victims may be expected to recover. The scenario given in movies such as Arachnophobia, where bite victims die within minutes, does not occur. One exception to this picture occurs in the case of very small children because the amount of venom dispersed throughout the body is many times the concentration in an adult. There is at least one recorded case of a small child dying within 15 minutes of a bite from a Sydney funnel-web spider; that event occurred before the development of an antivenom. Since the antivenom was developed there have been no fatalities due to this species.
The spider-bites documented as the most dangerous to humans are those of the Sydney funnel-web spider and the Brazilian wandering spider. These spiders are potentially more dangerous than widow spiders because they have longer fangs and can inject greater quantities of venom to greater depths. Phoneutria nigriventer has approximately 2 mg of venom, but frequently gives dry bites or at least does not deliver all of its available venom. Atrax robustus has approximately 1.7 mg of venom. Bites of Six-eyed sand spiders have been described as dangerous to humans, but there is a lack of proof for this,[24].25 though Sicarius venom has been shown to be fatal to rabbits.
The genus Latrodectus (of which the black widow spider is the most notorious) have been credited with killing more people per year, worldwide, than any other spider. Because they are not very large, they are much harder to detect than a large Brazilian wandering spider or a tarantula. Their venom is extremely potent. Compared to many other species of spiders, their chelicerae are not very large. In the case of a mature female, the hollow, needle shaped part of each chelicera, the part that penetrates the skin, is approximately 1 mm (0.04 in) long, sufficiently long to inject the venom to a dangerous depth. The males, being much smaller, can inject far less venom and inject it far less deeply. The actual amount injected, even by a mature female, is very small in physical volume (.02–.03 mg). When this small amount of venom is diffused throughout the body of a healthy, mature human, it usually does not amount to a fatal dose. Deaths in healthy adults from Latrodectus bites are rare in terms of the number of bites per thousand people. Only sixty-three deaths were reported in the United States between 1950 and 1989 (Miller, 1992). On the other hand, the geographical range of the widow spiders is very great. As a result, far more people are exposed, worldwide, to widow bites than are exposed to bites of more dangerous spiders, so the highest number of deaths worldwide are caused by members of the genus Latrodectus. Widow spiders have more potent venom than most spiders, and prior to the development of antivenom, 5% of bites resulted in fatalities, although comparable figures are not available for the other species.[25]
[edit] MeasurementsThe LD-50 (Median lethal dose) figures have limited utility since the effects of venoms differ widely from species to species. Before an antivenom was developed, deaths from Atrax and Hadronyche did occur, but the frequency of non-lethal bites is unknown. Some deaths from Phoneutria bites are reported, but much of their range is in the Amazon so reporting of bites may not be very complete.
Most LD-50 figures are based on experiments with laboratory mice. There are great differences in the sensitivities of various kinds of organisms to various kinds of venom. The relative sensitivities of mice to various venoms may not allow prediction of the exact degree of human sensitivity. So most of these figures can only give a rough approximation of the medical consequences of various spider bites to humans. A case in point are the Sicarius spp. The venom of these spiders is extremely active in laboratory animals, but there are few if any documented reports of Sicarius bites in humans.
DiagnosisAssumption that a reported injury was caused by a spider is the most common source of false reports, which in some cases have led to misdiagnosis and mistreatment, with potentially life-threatening consequences.[39] Many spider bites, including those by some dangerous species, are relatively painless at first and may go unnoticed if not directly observed. These bites may only be noticed later if serious symptoms appear.
Occasionally, infections of methicillin-resistant Staphylococcus aureus (MRSA) are misdiagnosed as necrotic spider bites; this can have severe consequences as a MRSA infection is frequently a medical emergency.[40]
[edit] ManagementMost spider bites are harmless, and require no specific treatment. Treatment of bites may depend on the type of spider thus capture of the spider—either alive, or in a well-preserved condition is useful.[citation needed]
In the case of bites by widow spiders, Australian venomous funnel-web spiders, or Brazilian wandering spiders, prompt medical attention should be sought as in some cases the bites of these spiders may develop into a medical emergency.[citation needed]
Treatment for non-poisonous spider bites include washing the bite with soap and water and ice to reduce inflammation.[5] Analgesics and antihistamines maybe used however antibiotics are not recommended unless there is also a bacterial infection present.[5]
[edit] NecrosisThere is no established treatment for necrosis. Recommendations include elevation and immobilization of the affected limb, application of ice, local wound care, and tetanus prophylaxis. Many other therapies have been used with varying degrees of success including hyperbaric oxygen, dapsone, antihistamines (e.g., cyproheptadine), antibiotics, dextran, glucocorticoids, vasodilators, heparin, nitroglycerin, electric shock, curettage, surgical excision, and antivenom. None of these treatments have been subjected to controlled, randomized trials to conclusively show benefit. In almost all cases, bites are self-limited and typically heal without any medical intervention.[4]
Dapsone is commonly used in the USA and Brazil for the treatment of necrosis. There have been conflicting reports about its efficacy and some have suggested it should no longer be used routinely, if at all.[41]
[edit] OtherStudies have shown surgical intervention is ineffective and may worsen outcome. Excision may delay wound healing, cause abscesses, and lead to objectional scarring.[42]
Use of antivenom for severe spider bites may be indicated, especially in the case of neurotoxic venoms.[43] Effective antivenoms exist for Latrodectus, Atrax, and Phoneutria venom. Recluse bites are treatable by antivenom; an antivenom for Loxosceles bites is available in South America, and it appears antivenom may be the most promising therapy. However, the recluse antivenom is most effective if given early, and because of the relatively painless bite delivered by recluses, patients do not often present until 24 or more hours after the event, possibly limiting the effect of this intervention.[44] Due to the risk of serum sickness, use of antivenom is generally not indicated unless serious symptoms are present, and/or a person fails to respond to other forms of treatment.
[edit] Epidemiology[edit] AustraliaA study of 750 definite spider bites in Australia indicated that 6% of spider bites cause significant effects, the vast majority of these being redback spider bites causing significant pain lasting more than 24 hours.[45]
[edit] United States The jumping spider is probably the most common biting spider in the United States,[46] the main species being Phidippus audax.[47] Bites from a jumping spider are usually painful, itchy and cause redness and significant swelling.[46]
The spiders of most concern in the United States, however, are brown recluse spiders and black widow spiders. Most recluse spider bites are minor with little or no necrosis. However, a small number of bites produce severe dermonecrotic lesions, and, sometimes, severe systemic symptoms, including organ damage. Rarely the bite may also produce the systemic condition with occasional fatalities.
Black widow spider bites may cause muscle cramps, but no one in the United States has died from a black widow spider bite in over 10 years.[46]
[edit] ClassificationA spider is classified as "venomous" if it is able to cause significant harm to humans.[5] Spiders having medically significant venom exist in all but the coldest parts of the world. There is general agreement on which spiders give bites that may produce lasting damage or death, but not such general agreement on how one might sort spiders identified by genus and species in order of their threat to humans.
The following types of spider are known to have medically significant bites, with symptoms ranging from localized pain all the way to severe tissue destruction and potential death. Spiders whose bites have caused fatalities which are well documented in the scientific literature are so indicated in the section headers. Only four genera (Phoneutria, Atrax, Latrodectus, and Loxosceles) are known to have killed humans; three other genera (Hadronyche, Missulena, and Sicarius) possess venom which toxicology studies have shown have lethal potential (being similar to Atrax and Loxosceles venom in composition). There are suspected but unconfirmed deaths reported in the literature from species in Tegenaria and Haplopelma.
There is more infomation on spiders within this source however not needed in the prevention of the bites themself.
Link:
en.wikipedia.org/wiki/Spider_bite
Spiders are active hunters and strongly rely on their bites to paralyze and kill their prey before consuming it. Since spiders are aware of the effect caused by their bites, they also widely bite on self-defense any intruder risking to damage individuals or their webs (i.e. bites are their naturally occurring defense mechanism). While many spiders will never attack animals larger than themselves, preferring to either run away or feign death[citation needed], some share a rather aggressive behavior and will do so even if no real danger exists[citation needed].
Only a minority of spider species possess chelicera strong enough to penetrate human skin, however due to their strong surviving potential, they are those most frequently encountered in human habitats. About 98% of the bites inflicted by these species are harmless,[1] but some symptoms can include necrotic wounds, systemic toxicity and, in some cases, death. Only some two hundred species in twenty genera (out of over 40,000 known species) are known to have serious, potentially lethal bites.[2]
In most cases of bites, the chief concern is the spider's venom, although in some cases medically non-significant spiders can transmit infectious diseases. Spiders regarded as dangerous possess venom that is toxic to humans, in quantities that can be delivered by a single bite. Only three spider families are known to be non-venomous, i.e. lacking venom glands or any proper way to deliver it. They are Uloboridae, Holarchaeidae and Liphistiidae. These spiders, however, do possess fangs and can deliver sharp, unpleasant bites. In addition, the fangs of Liphistiidae can often inflict infections spread through the skin, mostly due to their large size, which in theory could represent more danger than the bite of a non-lethal venomous spider species.
Spider bites may be misdiagnosed by both the general public and medical practitioners. Many other conditions both infectious and non-infectious can be confused with spider bites.[3] Many of these conditions are far more common and more likely to be the source of necrotic wounds.[4]
Signs and symptoms
A Brazilian man 31 hours after having been bitten on his face by a Loxoceles spider.
4 month after a brown recluse spider bite with scar remainingPain from non venomous spider bites typically lasts for 5 to 60 minutes while pain from venomous spider bites frequently lasts for greater than 24 hours.[5] The rate of a bacterial infection due to a spider bite is low (0.9%).[5]
[edit] PathophysiologyA primary concern of the bite of a spider is the effect of its venom. A spider envenomation occurs whenever a spider injects venom into the skin. Not all spider bites involve injection of venom into the skin, and the amount of venom injected can vary based on the type of spider and the circumstances of the encounter. With very few exceptions, such as the so-called camel spider (which is not a true spider), the mechanical injury from a spider bite is not a serious concern for humans. Some spider bites do leave a large enough wound that infection may be a concern, and other species are known to consume prey which is already dead, which also may pose a risk for transmission of infectious bacteria from a bite.[6] However, it is generally the toxicity of spider venom which poses the most risk to human beings; several spiders are known to have venom which can be fatal to humans in the amounts that a spider will typically inject when biting.
All spiders are capable of producing venom, with the exception of the hackled orb-weavers, the Holarchaeidae, and the primitive Mesothelae[citation needed]. (Other arachnids often confused with spiders, such as the harvestman and sun spiders, also do not produce venom). Nonetheless, only a small percentage of species have bites which pose a danger to people. Many spiders do not have mouthparts capable of penetrating human skin. While venoms are by definition toxic substances, most spiders do not have venom which is sufficiently toxic (in the quantities delivered[citation needed]) to require medical attention and, of those that do, only a few are known to produce fatalities[citation needed].
Spider venoms work on one of two fundamental principles; they are either neurotoxic (attacking the nervous system) or necrotic (attacking tissues surrounding the bite, and in some cases, attacking vital organs and systems)[citation needed].
[edit] Neurotoxic venomThe majority of spiders with serious bites possess a neurotoxic venom of some sort, though the specific manner in which the nervous system is attacked varies from spider to spider.[7][8][9]
Widow spider venom contains components known as latrotoxins, which cause the release of the neurotransmitter acetylcholine, stimulating muscle contractions. This can affect the body in several ways, including causing painful abdominal cramps, as well as interfering with respiration, and causing other systemic effects.[2]
The venom of Australasian funnel-web spiders and mouse spiders works by opening sodium channels, causing excessive neural activity which interferes with normal bodily function.
The venom of Brazilian wandering spiders is also a potent neurotoxin, which attacks multiple types of ion channels [10] In addition, the venom contains high levels of serotonin, making an envenomation by this species particularly painful.
[edit] Necrotic venomSpiders known to have necrotic venom are found in the family Sicariidae, a family which includes both the recluse spiders and the six-eyed sand spiders. Spiders in this family possess a known dermonecrotic agent sphingomyelinase D,[11][12] which is otherwise found only in a few pathogenic bacteria.[13][14] Some species in this family are more venomous than others; according to one study, the venom of the chilean recluse and several species of six-eyed sand spider indigenous to southern Africa, contains an order of magnitude more of this substance than do other Sicariidae spiders such as the brown recluse.[15] Bites by spiders in this family can produce symptoms ranging from minor localized effects, to severe dermonecrotic lesions, up to and including severe systemic reactions including renal failure, and in some cases, death.[16] Even in the absence of systemic effects, serious bites from Sicariidae spiders may form a necrotising ulcer that destroys soft tissue and may take months and very rarely years to heal, leaving deep scars. The damaged tissue may become gangrenous and eventually slough away. Initially there may be no pain from a bite, but over time the wound may grow to as large as 10 inches (25 cm) in extreme cases. Bites usually become painful and itchy within 2 to 8 hours, pain and other local effects worsen 12 to 36 hours after the bite with the necrosis developing over the next few days.[17]
Serious systemic effects may occur before this time, as the venom spreads throughout the body in minutes. Mild symptoms include nausea, vomiting, fever, rashes, and muscle and joint pain. Rarely more severe symptoms occur including hemolysis, thrombocytopenia, and disseminated intravascular coagulation.[18] Debilitated patients, the elderly, and children may be more susceptible to systemic loxoscelism. Deaths have been reported for both the brown recluse and the related South American species L. laeta and L. intermedia.
Numerous other spiders have been associated with necrotic bites in the medical literature. Examples include the Hobo spider and the Yellow Sac spider. However, the bites from these spiders are not known to produce the severe symptoms that often follow from a recluse spider bite, and the level of danger posed by each has been called into question.[19][20] So far, no known necrotoxins have been isolated from the venom of any of these spiders, and some arachnologists have disputed the accuracy of many spider identifications carried out by bite victims, family members, medical responders, and other non-experts in arachnology. There have been several studies questioning danger posed by some of these spiders. In these studies, scientists examined case studies of bites in which the spider in question was positively identified by an expert, and found that the incidence of necrotic injury diminished significantly when "questionable" identifications were excluded from the sample set.[21][22]
[edit] Comparative analysisIt is often asked which type of spider is the most "dangerous" in the world. There isn't a simple answer to this question, as there are many things which must be taken into account when considering the amount of danger posed by spider bites:
Firstly, it is often the case that a spider bite is "dry" – the skin may be pierced, but little or no venom is injected into the victim. In such an instance, little or none of the spider's dangerous potential for harm is manifested.
Secondly, there have been reports of spider bites (by spiders considered otherwise harmless) causing allergic reactions in some individuals, up to and including anaphylactic shock, a life-threatening condition (much the same as a sting from an ant, bee, or wasp may produce a harmful effect apart from the toxic quality of its venom).[23]
Thirdly, many spiders listed as dangerous are seldom encountered, or have dispositions that make them unlikely to bite despite the high toxicity of their venom.
Finally, little is known about the toxicity of many spiders, due to their infrequent encounters with humans; the list of venomous spiders is limited to those that are linked to medical events in humans or who otherwise have been extensively studied.
It should also be noted that, for healthy adults, a bite by even the most toxic spiders on the list may require hours before death ensues; if timely appropriate emergency medical treatment is administered, victims may be expected to recover. The scenario given in movies such as Arachnophobia, where bite victims die within minutes, does not occur. One exception to this picture occurs in the case of very small children because the amount of venom dispersed throughout the body is many times the concentration in an adult. There is at least one recorded case of a small child dying within 15 minutes of a bite from a Sydney funnel-web spider; that event occurred before the development of an antivenom. Since the antivenom was developed there have been no fatalities due to this species.
The spider-bites documented as the most dangerous to humans are those of the Sydney funnel-web spider and the Brazilian wandering spider. These spiders are potentially more dangerous than widow spiders because they have longer fangs and can inject greater quantities of venom to greater depths. Phoneutria nigriventer has approximately 2 mg of venom, but frequently gives dry bites or at least does not deliver all of its available venom. Atrax robustus has approximately 1.7 mg of venom. Bites of Six-eyed sand spiders have been described as dangerous to humans, but there is a lack of proof for this,[24].25 though Sicarius venom has been shown to be fatal to rabbits.
The genus Latrodectus (of which the black widow spider is the most notorious) have been credited with killing more people per year, worldwide, than any other spider. Because they are not very large, they are much harder to detect than a large Brazilian wandering spider or a tarantula. Their venom is extremely potent. Compared to many other species of spiders, their chelicerae are not very large. In the case of a mature female, the hollow, needle shaped part of each chelicera, the part that penetrates the skin, is approximately 1 mm (0.04 in) long, sufficiently long to inject the venom to a dangerous depth. The males, being much smaller, can inject far less venom and inject it far less deeply. The actual amount injected, even by a mature female, is very small in physical volume (.02–.03 mg). When this small amount of venom is diffused throughout the body of a healthy, mature human, it usually does not amount to a fatal dose. Deaths in healthy adults from Latrodectus bites are rare in terms of the number of bites per thousand people. Only sixty-three deaths were reported in the United States between 1950 and 1989 (Miller, 1992). On the other hand, the geographical range of the widow spiders is very great. As a result, far more people are exposed, worldwide, to widow bites than are exposed to bites of more dangerous spiders, so the highest number of deaths worldwide are caused by members of the genus Latrodectus. Widow spiders have more potent venom than most spiders, and prior to the development of antivenom, 5% of bites resulted in fatalities, although comparable figures are not available for the other species.[25]
[edit] MeasurementsThe LD-50 (Median lethal dose) figures have limited utility since the effects of venoms differ widely from species to species. Before an antivenom was developed, deaths from Atrax and Hadronyche did occur, but the frequency of non-lethal bites is unknown. Some deaths from Phoneutria bites are reported, but much of their range is in the Amazon so reporting of bites may not be very complete.
Most LD-50 figures are based on experiments with laboratory mice. There are great differences in the sensitivities of various kinds of organisms to various kinds of venom. The relative sensitivities of mice to various venoms may not allow prediction of the exact degree of human sensitivity. So most of these figures can only give a rough approximation of the medical consequences of various spider bites to humans. A case in point are the Sicarius spp. The venom of these spiders is extremely active in laboratory animals, but there are few if any documented reports of Sicarius bites in humans.
DiagnosisAssumption that a reported injury was caused by a spider is the most common source of false reports, which in some cases have led to misdiagnosis and mistreatment, with potentially life-threatening consequences.[39] Many spider bites, including those by some dangerous species, are relatively painless at first and may go unnoticed if not directly observed. These bites may only be noticed later if serious symptoms appear.
Occasionally, infections of methicillin-resistant Staphylococcus aureus (MRSA) are misdiagnosed as necrotic spider bites; this can have severe consequences as a MRSA infection is frequently a medical emergency.[40]
[edit] ManagementMost spider bites are harmless, and require no specific treatment. Treatment of bites may depend on the type of spider thus capture of the spider—either alive, or in a well-preserved condition is useful.[citation needed]
In the case of bites by widow spiders, Australian venomous funnel-web spiders, or Brazilian wandering spiders, prompt medical attention should be sought as in some cases the bites of these spiders may develop into a medical emergency.[citation needed]
Treatment for non-poisonous spider bites include washing the bite with soap and water and ice to reduce inflammation.[5] Analgesics and antihistamines maybe used however antibiotics are not recommended unless there is also a bacterial infection present.[5]
[edit] NecrosisThere is no established treatment for necrosis. Recommendations include elevation and immobilization of the affected limb, application of ice, local wound care, and tetanus prophylaxis. Many other therapies have been used with varying degrees of success including hyperbaric oxygen, dapsone, antihistamines (e.g., cyproheptadine), antibiotics, dextran, glucocorticoids, vasodilators, heparin, nitroglycerin, electric shock, curettage, surgical excision, and antivenom. None of these treatments have been subjected to controlled, randomized trials to conclusively show benefit. In almost all cases, bites are self-limited and typically heal without any medical intervention.[4]
Dapsone is commonly used in the USA and Brazil for the treatment of necrosis. There have been conflicting reports about its efficacy and some have suggested it should no longer be used routinely, if at all.[41]
[edit] OtherStudies have shown surgical intervention is ineffective and may worsen outcome. Excision may delay wound healing, cause abscesses, and lead to objectional scarring.[42]
Use of antivenom for severe spider bites may be indicated, especially in the case of neurotoxic venoms.[43] Effective antivenoms exist for Latrodectus, Atrax, and Phoneutria venom. Recluse bites are treatable by antivenom; an antivenom for Loxosceles bites is available in South America, and it appears antivenom may be the most promising therapy. However, the recluse antivenom is most effective if given early, and because of the relatively painless bite delivered by recluses, patients do not often present until 24 or more hours after the event, possibly limiting the effect of this intervention.[44] Due to the risk of serum sickness, use of antivenom is generally not indicated unless serious symptoms are present, and/or a person fails to respond to other forms of treatment.
[edit] Epidemiology[edit] AustraliaA study of 750 definite spider bites in Australia indicated that 6% of spider bites cause significant effects, the vast majority of these being redback spider bites causing significant pain lasting more than 24 hours.[45]
[edit] United States The jumping spider is probably the most common biting spider in the United States,[46] the main species being Phidippus audax.[47] Bites from a jumping spider are usually painful, itchy and cause redness and significant swelling.[46]
The spiders of most concern in the United States, however, are brown recluse spiders and black widow spiders. Most recluse spider bites are minor with little or no necrosis. However, a small number of bites produce severe dermonecrotic lesions, and, sometimes, severe systemic symptoms, including organ damage. Rarely the bite may also produce the systemic condition with occasional fatalities.
Black widow spider bites may cause muscle cramps, but no one in the United States has died from a black widow spider bite in over 10 years.[46]
[edit] ClassificationA spider is classified as "venomous" if it is able to cause significant harm to humans.[5] Spiders having medically significant venom exist in all but the coldest parts of the world. There is general agreement on which spiders give bites that may produce lasting damage or death, but not such general agreement on how one might sort spiders identified by genus and species in order of their threat to humans.
The following types of spider are known to have medically significant bites, with symptoms ranging from localized pain all the way to severe tissue destruction and potential death. Spiders whose bites have caused fatalities which are well documented in the scientific literature are so indicated in the section headers. Only four genera (Phoneutria, Atrax, Latrodectus, and Loxosceles) are known to have killed humans; three other genera (Hadronyche, Missulena, and Sicarius) possess venom which toxicology studies have shown have lethal potential (being similar to Atrax and Loxosceles venom in composition). There are suspected but unconfirmed deaths reported in the literature from species in Tegenaria and Haplopelma.
There is more infomation on spiders within this source however not needed in the prevention of the bites themself.
Link:
en.wikipedia.org/wiki/Spider_bite