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May 18, 2005

Galen's Log: Grand Rounds 34 and an MRSA-spreading Spider

Galen's Log just hosted Grand Rounds 34, the latest in a weekly linked tour of the medical blogosphere. Follow this link to the humorous post introducing a number of other bloggers discussing things medical.

Update 18 May 2005: Please Note: After reading my musings below, Galen (himself) e-mailed to explain that his post was meant as an in-joke for doctors, who frequently encounter patients claiming their skin infections were caused by the bite of an unseen spider. The particular species of Loxosceles recluse mentioned in his article does not, in fact, exist.

I'll leave my clueless ramblings posted here, but as you read remember that Galen's article was written in jest. I appreciate his providing me the nod 'n' wink.

Scrolling down the page after reading Grand Rounds -- which includes a link to one nephrologist's discovery of MRSA infections -- I ran into another, pretty surprising, mention of MRSA. Seems that recluse spiders found in central and southwestern USA are not only fairly poisonous, but are also carriers and transmitters of MRSA. The post discusses one species in particular (Loxosceles mersenius), includes a hideous picture of an infected bite, and these remarks:

98% [!!] of wound cultures in this condition are positive for methicillin-resistant Staph aureus [MRSA]. A recent study of vancomycin in Loxosceles mersenius cases versus oral clindamycin showed a 34% improvement in subjective symptoms after 48 hours and an average of 4 days earlier healing time. Oral analgesics are typically sufficient for pain control.

The transmission of pathological organisms in the insect kingdom is well documented, though this is the first documented case with arachnids. Researchers are debating whether Loxosceles mersenius is merely a coincidental host to MRSA or if it plays an active role in the spider's life cycle. The bacteria seems too slow acting to assist the spider in capturing or aiding in the digestion of prey.

Galen also notes that since these spiders occupy the backs of closets and are so rarely seen, many bites just show up without any whacked spider to blame. So that raises some questions in my peabrain:
  • If these spiders are, as the name states, so reclusive, where are they picking up this MRSA bacteria?
  • Is the MRSA already on the skin of bitten people who get the infection, then introduced into both the wound and the spider during the bite?
  • Or, does the spiders' carrying MRSA mean that this superbug is:
    1) so widespread that even shy spiders found it, or
    2) it's developed in the wild (perhaps in antibiotic-fed farm animals) as well as in the hospital environment?

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