When You Think It's a Spider Bite But It's Not

Hospital emergency departments get a lot of infected sores that are blamed on spider bites. In reality, most of the "bites" are probably just nasty bacterial infections. In most cases, the spider is nowhere to be found.

Not having the spider makes it hard to positively identify a spider bite. In the United States, the brown recluse spider is often blamed for bites, but the brown recluse only lives in a few states in the southeast part of the country. There are poisonous spiders related to the recluse living in other areas, but they are not nearly as dangerous as their Dixieland cousins.

Hobo spiders and black widows get blamed nearly as often as the brown recluse.

Doctors are almost as guilty as patients for incorrectly diagnosing ugly skin ulcers as spider bites. These pictures all show sores that the patient—and in some cases, the doctor—thought were spider bites.

Hives or Shingles?

Rash consistent with shingles
Even though he thought it was a spider bite, Jose's rash looks like classic shingles. Jose Luis Balarezo Gardiol

After Jose felt what he thought was a spider bite him in Peru, he developed a rash with muscle pain that seemed to be relieved by an antihistamine (a Peruvian equivalent of Claritin). The raised rash does resemble hives in the pictures provided by Jose, but the rash also resembles another common condition: shingles.

Jose was not able to see a doctor to treat this rash. He describes it as traveling from the site of the original bite on his back all the way around to his chest. That one-sided line is typical in shingles, but could also be an allergic reaction.

There is really no way to tell what Jose has without seeing him in person. Shingles—also known as herpes zoster—comes from the Varicella-zoster virus, the same virus that causes chicken pox.

If Jose did have an allergic reaction, allergic reactions to bug and spider bites can be deadly if they develop into anaphylactic shock. Usually, if anaphylaxis is going to develop it happens fairly quickly after the bite. Bee stings are commonly considered the most likely to lead to anaphylaxis.

Bites on Both Feet? Probably Not.

Tissue damage on feet of a person with diabetes
The family of this woman with diabetes believes the original tissue damage started with spider bites. Ivonne H.

Ivonne H. shared this picture of her mother's tissue damage following what the family believes were brown recluse spider bites. According to Ivonne, her mother was bitten twice; in Alaska on one foot and in Utah on the other. Ivonne says her mom felt the first bite. While walking, Ivonne's mom felt a sharp pain and ignored it, thinking it was a lost needle in the carpet.

Ivonne's mother began feeling pain in her leg and went to the doctor, who diagnosed the pain as being "weather related." After a while, the pain got worse and the damage became visible. Ivonne describes the wound as looking like a "colander." Eventually, part of her mother's right foot had to be amputated.

But Is It a Spider Bite?

Reading Ivonne's account of her mother's struggle, I can't help but wonder if a spider ever had anything to do with the wound. Ivonne says her mom had diabetes, which often leads to circulation problems that are especially bad in the feet and legs. Many people with diabetes suffer from cellulitis (inflamed skin cells) that can get bad enough to need amputation.

I'm also skeptical because Ivonne's mom was supposed to have two separate spider bites, one on each foot. Spider bites are rare; brown recluse bites are even rarer yet. The odds of getting a brown recluse bite on one foot in Alaska followed by a brown recluse bite on the other foot in Utah—neither state is in the brown recluse's known habitat—are well beyond my mathematic ability to calculate.

Staphylococcus aureas or group A streptococcus both cause skin infections that are regularly mistaken for spider bites. Combine that with the fact that people with diabetes are at such a high risk for foot infections and you have the perfect storm for bilateral (both right and left) tissue damage of the type in the picture.

Whether caused by spider bites or skin infections, wounds like these are painful and dangerous. It's important to seek medical attention when a wound starts to form. Your doctor may be able to identify the cause and treat it.

Did the Mailbox Bite Her?

Discolored blister
An expanding lesion with a blister in the middle. Nicole Horstmann

A reader sends in this picture from what she believes is a bug bite on her mother.

Mom got ambushed by something at the mailbox on a Thursday and this was how the lesion looked on the following Saturday. Lots of confirmed spider bites show expanding lesions like this one, but infections can do that, too. As we've seen before, the blister can come from a bite, an infection or something else entirely.

There are very few welts or lesions that can be positively identified as a particular bug or spider. So often, readers want to know what kind of bug did the damage, but the answer has to be: what kind of bug did you see biting you? If the critter wasn't caught in the act, then there is little chance we're going to solve the case.

Ultimately if the lesion keeps growing, starts oozing, smells bad, gets hot, turns black, starts bleeding, the victim gets a fever or starts showing other signs of an infection, it's time to go to the doctor.

Maybe a Spider Broke the Skin

An infected lesion
This lesion is definitely infected. Kenneth Walker

While this wound was attributed to a spider bite, there was no spider to identify. Whether or not the original break in the skin came from a spider, the wound is definitely infected. The patient sought help after 2 days (this image) because the wound was draining pus.

Getting help was the right thing to do. Evidence abounds that what many patients call "spider bites" are really methicillin-resistant Staphylococcus aureus (MRSA) infections. MRSA can lead to dead tissue (necrotizing fasciitis) like that pictured here. MRSA is also fast becoming the most common diagnosis for skin lesions like these treated in the emergency department.

Blister on the Toe Is Not a Spider Bite

Blister at the base of the toe
This blister was blamed on a spider, but it turned out to be an infection. Bridget Wuerdeman

Bridget writes that this blister has led to antibiotic therapy and is extremely painful. She doesn't provide a species or a spider to look at, which leads me to the same place I always go. Unless the spider is caught in the act, odds are we're looking at some sort of staph or strep infection.

Bridget says she popped the blister after 3 days because she couldn't take the pain and pressure. She was advised not to by her physician but did anyway. There's not really a right or wrong here, the blister would probably break and drain at some point, but you don't want to encourage it prematurely. She could have introduced another form of bacteria and possibly made the infection worse.

It turns out this is not a spider bite at all. It is a skin infection from MRSA. Hopefully, Bridget followed the rest of doc's orders, especially about taking all her antibiotics. Bridget was right in seeking help for this blister. She hoped that sharing it would help others recognize when a blister is more than ill-fitting shoes. Thanks to her for sharing.

Sources:

Baxtrom, C., et al."Common house spiders are not likely vectors of community-acquired methicillin-resistant Staphylococcus aureus infections." Journal of medical entomology. Sep 2006.

Moran, G.J., et al."Methicillin-resistant S. aureus infections among patients in the emergency department." New England journal of medicine. 17 Aug 2006.

Pagac, B.B., et al."Skin lesions in barracks: consider community-acquired methicillin-resistant Staphylococcus aureus infection instead of spider bites." Military medicine. Sep 2006.

Vetter, Richard S. and Stocks, Ian C. "Reports of Envenomation by Brown Recluse Spiders Exceed Verified Specimens of Loxosceles Spiders in South Carolina.Journal of the American Board of Family Medicine. 20 (5): 483-488 (2007)

Young, L.M., and Price, C.S. "Community-Acquired Methicillin-Resistant Staphylococcus aureus Emerging as Important Cause of Necrotizing Fasciitis." Surgical infections. 9 Apr 2008.Frithsen, Ivar L.,

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