Brown Recluse Encounters
Humans have long feared spiders. Actually, only a small percentage of spider species are capable of piercing human skin and injecting venom. A few such species live in the United States. Today we will discuss the health impact of Loxoceles reclusa, the brown recluse spider.
The Spider
Its name suits its behavior, for the brown recluse prefers dark dry areas such as leaf, wood and rock piles, and closets, boxes, clothing and beds. No ornate web-like those found under lights or in gardens; a perfunctory one in a dark corner is cast, but these creatures roam freely in the dark, seeking insect meals.
The brown recluse spider inhabits only one geographic expanse on the globe-an area ranging from Kansas east through Missouri to western Ohio, sweeping south to the Gulf coast. See map at:
http://z.about.com/d/insects/1/0/Z/5/-/-/colorloxmap.gif
L. reclusa is a 6-eyed spider-an unusual trait, seeing that most spiders have eight eyes-4 pairs. The brown recluse spider has 3 pairs of eyes, one pair front and center, the other pairs on each side. This feature is quite important in the identification of L. reclusa, since the violin or "fiddle" on its back is shared by other spider species, but none of these others possesses 6 eyes.
The brown recluse spider has a characteristic stance and gait, with rather long, tapering legs evenly splayed out-the second pair of legs slightly longer than the others, and a steady, methodical ambulation, with galloping forward when threatened by man. Most are brown, but a few may be a dirty yellow; the size is often that of a nickel up to a half-dollar, though a 4 cm leg-to-leg span has been reported.
The Encounter
A spider bite is classified as a trauma and a poisoning. All spiders carry venom. The threat of a spider to man rests on its ability to break the cutaneous barrier and inject venom. Most spiders are not a threat to the health and well being of man, because they lack the ability to introduce venom. A granddaddy longlegs owns very potent venom, but is unable envenomate humans.
Often an encounter with a brown recluse is not so much awareness of the bite as the startling perception of a writhing, crawling "bug" caught between clothing and the skin. The spider is generally dismembered and killed in the ensuing struggle, but collection of the disrupted specimen in an envelope or jar containing rubbing alcohol should be taken to the medical caregiver.
The Venom
Loxaceles reclusa venom contains sphingomyelinase D2, which causes platelet aggregation. This spider has highly efficient mouthparts, with morbidity related to the amount of venom injected, the immune status of the subject, and the age (children under 7 years and the elderly have increased risk of severe toxicity). Overall mortality of brown recluse spider bites is well below 1%.
The Reaction
In reactive individuals, minutes to hours after envenomation, itching, pain, and redness define the bite site; later a small blister forms and a bluish ring surrounds this vesicle. Aggregated platelet plugs interrupt blood flow in the area of the toxin. Fever, nausea and vomiting, joint pains and rash may appear. Over 24 hours, the blister becomes a black eschar, which later sloughs off, leaving an ulcer. This process is known as cutaneous loxoscelism.
The venom may in rare cases affect circulation to vital organs, causing hemolytic anemia, DIC (Disseminated Intravascular Coagulation), and ARF (Acute Renal Failure). This process occurs in conjunction with skin manifestations, and is called viscerocutaneous loxoscelism.
Treatment
Treatment is usually secondary, for the major symptoms appear after ischemic damage has occurred. Most authors recommend bringing the victim's tetanus status up to the current recommended level. Antibiotics may be used topically and/or systemically. Use of corticosteroids is controversial. Skin grafts may be required to reduce disfigurement from ulcer cicatrization (scar formation).
An antivenin for treatment of loxoscelism is produced at the Instituto Butantan in Sao Paulo, Brazil. None is available in the USA.
Prevention
Vigilance in endemic areas, particularly in warm months. Wood piles, leaf piles, docked boats in the morning, unswept garages and basements, stacked, honeycombed cardboard boxes, stored, piled clothing, doorways to exterior, bedding, dust ruffles-anyplace ordinarily dark and dry where encounters with light occur on human entry.
If entering a high-risk exterior area, wear leather gloves, long-sleeved shirt or jacket, long pants covering socks, boots, hat, and insect repellant. Interior exposures-gloves, long sleeves and pants, socks and shoes for cleaning closets, around and under beds, and in garages.
Before donning stored clothing, shake it out vigorously. Turn down bedding in good light before retiring for the night. If you put on clothing and believe there may be a spider in it, try to relax and carefully remove the article of clothing-if you see or feel a bite and you see that it's a spider, try to safely collect it, dead or alive, to help in the treatment of your bite.
Afterword
Studies have suggested that the population of L. reclusa in various states is far below the rate of brown spider bite morbidity reports, owing possibly to occasional diagnosis of MRSA (Methicillin Resistant Staphylococcus Aureus) infections as brown recluse spider bites. Antibiotic therapy is applied to both conditions, but the accuracy of reporting cutaneous and viscerocutaneous loxoscelism is important. Specimens of suspected spiders should be retrieved and taken to medical providers whenever possible.
References
1] The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.
2] Pediatric critical care medicine: basic science and clinical evidence By Derek S. Wheeler, Hector R. Wong, Thomas P. Shanley 2007
3] Cecil Textbook of Internal Medicine 1979, p.115
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