Brown recluse spider

From Wikipedia, the free encyclopedia

Brown recluse spider
Scientific classification
Kingdom: Animalia Phylum: Arthropoda Class: Arachnida Order: Araneae Family: Sicariidae Genus: Loxosceles Species: L. reclusa
Binomial name
Loxosceles reclusa Gertsch & Mulaik, 1940

The brown recluse spider is a spider, Loxosceles reclusa, of the family Sicariidae (formerly of the family Loxoscelidae). It is usually between ¼ and ¾ inch (6-20mm) but may grow larger. It is brown and usually has markings on the dorsal side of its cephalothorax, with a black line coming from it that looks like a violin with the neck of the violin pointing to the rear of the spider, resulting in the nickname "fiddleback spider" or "violin spider". Coloring varies from light tan to brown and the violin marking may not be visible. Since the "violin pattern" is not diagnostic, and other spiders may have similar marking (i.e. cellar spiders (Pholcidae family) and pirate spiders (Mimetidae family)), for purposes of identification it is far more important to examine the eyes. Differing from most spiders, which have 8 eyes, recluse spiders have 6 eyes arranged in pairs (dyads) with one median pair and 2 lateral pairs. Only a few other spiders have 3 pairs of eyes arranged this way (e.g., scytodids), and recluses can be distinguished from these as recluse abdomens have no coloration pattern nor do their legs, which also lack spines.^[1] Recluse spiders build irregular webs that frequently include a shelter consisting of disorderly threads. These spiders frequently build their webs in woodpiles and sheds, closets, garages, and other places that are dry and generally undisturbed. Unlike most web weavers, they leave these webs at night to hunt. Males will move around more when hunting while females don't usually stray far from their web.

Contents 1 Distribution 2 Venomous bite 3 Bite Treatment 3.1 Specific treatments 4 Misdiagnoses 5 Footnotes 6 External links

[edit] Distribution

The brown recluse spider is native to the United States from the southern Midwest south to the Gulf of Mexico ^[2] The native range lies roughly south of a line from southeastern Nebraska through southern Iowa, Illinois, and Indiana to southwestern Ohio. In the southern states, it is native from central Texas to western Georgia. They are generally not found west of the Rocky Mountains.^[3] A related species, the brown violin spider (Loxosceles rufescens), is found in Hawai'i.^[4]

[edit] Venomous bite

As indicated by its name, this spider is not aggressive and usually bites only when pressed against human skin, such as when tangled up within clothes, bath towels, or in bedding.^[5]. In fact, many wounds that are necrotic and diagnosed as brown recluse bites can actually be methicillin resistant Staphylococcus aureus (MRSA). Actual brown recluse bites are rare. Brown recluse bites may produce a range of symptoms known as loxoscelism. There are two types of loxoscelism: cutaneous (skin) and systemic (viscerocutaneous).

Most bites are minor with 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 a systemic condition with occasional fatalities. Most fatalities are in children under 7 or those with a weaker than normal immune system. For a comparison of the toxicity of several kinds of spider bites, see the list of spiders having medically significant venom.)

A minority of bites form a necrotizing ulcer that destroys soft tissue and may take months and very rarely years to heal, leaving deep scars. There have been no known cases of actual brown recluse bites sites taking years to heal and can usually be attributed to a systemic infection or disease such as diabetes. The damaged tissue will become gangrenous and eventually slough away. The initial bite frequently cannot be felt and there may be no pain, 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.^[6] If the wound is weepy or moist and red looking, it is likely not a recluse bite because the venom actually seals off the capillaries and produces a dry wound. If the wound develops a lump or swelling this is usually indicative of another arachnid or insect as the venom of a recluse does not produce swelling.

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.^[7] 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. Other "Recluse" species such as the Desert Recluse (found in the desert southwestern United states) are reported to have caused necrotic bite wounds.

Numerous other spiders have been associated with necrotic bites in the medical literature. A partial list includes the hobo spider, the white-tailed 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. ^[8][9] 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. ^[10][11]

[edit] Bite Treatment

First aid involves the application of an ice pack to control inflammation, the application of aloe vera to soothe and help control the pain, and prompt medical care. If it can be easily captured, the spider should be brought with the patient in a clear, tightly closed container so it may be identified. However, by the time the bite is noticed any spider found nearby is not likely to be the culprit.

There is no established treatment for necrosis. Routine treatment should 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.^[3]

[edit] Specific treatments

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.^[12]

Wound infection is rare. Antibiotics are not recommended unless there is a credible diagnosis of infection.^[13]

Studies have shown surgical intervention is ineffective and may worsen outcome. Excision may delay wound healing, cause abscesses, and lead to objectional scarring.^[14]

Anecdotal evidence suggests benefit can be gained with the application of nitroglycerin patches.^[15] The brown recluse venom is a vasoconstrictor, and nitroglycerin causes vasodilation, allowing the venom to be diluted into the bloodstream, and fresh blood to flow to the wound. Theoretically this prevents necrosis, as vasoconstriction may contribute to necrosis. However, one scientific animal study found no benefit in preventing necrosis, with results showing it increased inflammation and it caused symptoms of systemic envenoming. The authors concluded the results of the study did not support the use of topical nitroglycerin in brown recluse envenoming.^[16]

Antivenom, available in South America, appears to be the most promising therapy. However, antivenoms are most effective if given early and because of the painless bite patients do not often present until 24 or more hours after the event, possibly limiting the effect of this intervention.^[17]

[edit] Misdiagnoses

It is estimated that 80% of reported brown recluse bites may be misdiagnoses. The misdiagnosis of a wound as a brown recluse bite could delay proper treatment of serious diseases.^[3] There is now a ELISA-based test for brown recluse venom that can determine if a wound is a brown recluse bite, although it is not commercially available and not in routine use.^{[18] [3]}

There are numerous documented infectious and noninfectious conditions (including pyoderma gangrenosum, bacterial infections by Staphylococcus and Streptococcus, herpes, diabetic ulcer, fungal infections, chemical burns, toxicodendron dermatitis, squamous cell carcinoma, localized vasculitis, syphilis, toxic epidermal necrolysis, sporotrichosis, and Lyme disease) that produce wounds that have been initially misdiagnosed as recluse bites by medical professionals; many of these conditions are far more common and more likely to be the source of mysterious necrotic wounds, even in areas where recluses actually occur.^[3]

Reported cases of bites occur primarily in Arkansas, Texas, Kansas, Missouri, Colorado, and Oklahoma. There have been many reports of brown recluse bites in California (and elsewhere outside the range of the brown recluse); however the brown recluse is not found in California^[19] (though a few related species may be found there, none of which has been shown to bite humans). Many arachnologists believe that many bites attributed to the brown recluse in the West Coast are not spider bites at all, or possibly instead the bites of other spider species; for example, the bite of the hobo spider has been reported to produce similar symptoms, and is found in the northwestern United States and southern British Columbia in Canada. However, the toxicity of the hobo spider has been called into question as bites have not been proven to cause necrosis, and the spider is not considered a problem in its native Europe.^[20]

[edit] Footnotes

[edit] External links

• Myth of the Brown Recluse (Fact, Fear, and Loathing)
• Description of brown recluse
• Emedicine datasheet
• Illinois and Iowa Brown Recluse Project requesting specimens from public