Brown Recluse Encounters

 

Spiders have long been feared by humans.  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.

 

L. reclusa is a 6-eyed spider-an unusual trait, seeing that most spiders have eight eyes--4 pairs.  The brown spider has 3 pairs of eyes, one pair front and center, the other pairs on each side.  This feature is quite important to identification of L. reclusa, since the violin or "fiddle" on its back is shared by other spider species, but none of the other "fiddlers" 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 rare lunges forward.  Most are brown, but a few may be a dirty yellow; the size is often the size of a nickel or 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 specimen in an envelope or jar containing rubbing alcohol, will be helpful later.  Most brown recluse bites are minor and do not cause significant morbidity.

 

Loxaceles reclusa venom contains sphingomyelinase D2 which causes platelet aggregtion.  This spider has highly efficient mouthparts, with fangs capable of injecting 10 times as much venom as a black widow spider. Morbidity and mortality is low, and reflects the amount of venom injected, the immune status of the subject, and age (children under 7 years and the elderly have increased risk of toxicity).  Looking at all brown recluse spider bites mortality is less than 1%.

 

A severe reaction  called cutaneous loxoscelism  accompanied by fever and chills, nausea and vomiting, joint pains, and a rash, rarely occurs.    Minutes to hours after envenomation, itching, pain and redness define the bite site; later a small blister forms and a bluish ring may surround the lesion.  Platelet plugs have interrupted blood flow in the area of the toxin. Over 24 hours, the blister becomes a black eschar, which later sloughs off, leaving an ulcer.  

 

Severe venom toxicity may affect circulation to vital organs, causing hemolytic anemia, DIC, (Disseminated Intravascular Coagulopathy), and ARF (Acute Renal Failure), and rarely death.  This process occurs in conjunction with skin manifestations, known as viscerocutaneous loxoscelism.

 

Treatment

 

 

Treatment is usually secondary;  major symptoms appear after ischemic damage has occurred.  Most authors recommend bringing the victim's tetanus status up to the recommended level.  Antibiotics may be used topically and systemically.  Use of corticosteroids is controversial.  Skin grafts may be required to reduce disfigurement from ulcer cicatrization.

 

An antivenin treatment for loxoscelism has been produced at the Instituto Butantan in Sao Paulo, Brazil; it  is not is  available in the USA.

 

 

 

Prevention

 

Awareness of the higher risk of encountering L. reclusa in endemic states (the  states containing or bordering on  "Tornado Alley") leads to vigilance and behaviors which reduce the chance of an unprepared encounter with a "Fiddleback."  

Clothes stored in closets should be shaken out before donning.  Leather  or other protective  gloves should be worn when clearing  lawn detritus, working around woodpiles, closets, garages, stored or docked boats.  Hand protection is important cleaning around beds,  dust ruffles.  It is important to  inspect bed linens prior to retiring, hanging clothing and shoes, shaking as needed, especially in the spring and fall, when the spiders egress and ingress, respectively.  Travelers to the endemic areas should take the usual precautions of denizens.  

Wear insect repellants in high risk areas (property known to be heavily infested),  and shoes, socks, jeans, long-sleeved shirts, jackets, bandanas, hats, as well.  

 

If caught in a close encounter, remain calm and passive, minimize sudden jerking movements and carefully remove harboring clothing.  Keep yard, garage, home highly clean.  Use of "glue cards" under beds, in closets, etc. to trap spiders may be helpful, and  give an idea of the level of infestation--get professional extermination help as needed.

 

Afterword

 

When human envenomation creates a threat, potency and nature of the venom define the health risk.  Latrodectus mactans-the Black Widow spider-has a neurotoxic venom with an LD-50 = 0.002 mg/kg, i.e. half the population of experimental animals exposed to 0.002 mg venom per kg body weight died.  It does not have a high capacity fang injection system, but is usually able to, in self defense, inject 0.02 mg of venom per kg of the recipient.   

Prior  to the development of Antivenin (Merck), which neutralizes black  spider venom, human mortality from such bites was 5%.  Today it is well below 1%.

 

Studies have suggest that the population of L. reclusa in various states is far below the rate of brown spider bite morbidity reports, owing possibly to confusion of the diagnosis with MRSA (Methicillin Resistant Staph Aureus) infections.  It is highly likely that brown recluse spider populations are greater than reports of sampling and public reporting owing to it reclusive nature. 

Antibiotic therapy is applied to both conditions, but the accuracy of reporting cutaneous and viscerocutaneous loxocelism is of critical importance. Specimens of spiders suspected of envenomation should be cautiously 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.115Describe New Article Submission here.

Notes: 1] The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved. I made some corrections in syntax and flow.9/26/2009 Thanks, DR3. 2] Pediatric critical car

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