This
is another ‘catch-all’ term for a variety of conditions that can
include bacterial, fungal, or environmental factors. In most forms of
shell rot, micro-organisms get under the protective layers of the
scutes and begin to ‘eat away’ at the tissues they find there. This
means that there needs to be a pathogen in the habitat, and usually
some form of damage to allow it to get under the top layer of scutes.
An example of a specific form of this type of shell rot is Septic
Cutaneous Ulcerative Disease (SCUD), which is caused by the bacteria Citobacter
freundii,
most often associated with shellfish. SCUD is most often associated with
aquatic chelonians.

‘Wet’
shell rot (dark pockets or pits, bad smell, etc.) is most often bacterial, while ‘dry’ shell rot (‘cheesy’ growths) is rarer and
usually fungal, but any form of rot causes damage that invites
secondary infections and other complications. Shell rot can eat deeply
into the shell, causing more severe issues, and even death.

Prevention

• Minimize the growth of
  bacteria, viruses, molds and
  mildew in the habitat.
• Arrange things to minimize scratches,
  abrasions, and
  chips to the shell.
• Prevent overly-wet substrates. These conditions can lead to environmental ‘rots’ that behave like ‘immersion foot’ does for humans. In my opinion and experience, wet acidic
  materials such as sphagnum mosses seem to make things worse.
• Bacterial and fungal forms of shell rot are infectious,
  so
  new animals should be quarantined and if one animal shows it, all
  animals should be monitored.

Treatment

1. Isolate the affected
   tortoise(s) someplace with a dryer, cleaner substrate (see Nursing Care).
2. Correct any
   issues in the habitat, environment, cares, and diet.
3. Clean the
   affected area with gentle scrubbing or
   scraping to remove
   loosened materials. Try to remove all dead, dried-out, or damaged scute
   materials, but do not force anything.
4. Swab
   the area completely
   with a multipurpose skin disinfectant such as Betadine Solution. Let
   dry completely. Betadine is effective against many micro-organisms, but
   also inhibits healthy growth so do not use it past the first 2-3 days. This may be all you need to do for a minor case.
5. Treat the
   affected area twice a day with an antibiotic ointment,
   preferably something like silver

   sulfadiazine ointment or 2%

   mupirocin ointment. Keep the tortoise on newspaper or paper towel
   for
   a couple hours or so to let the ointment work.

6. Repeat ointment
   for about a week. Re-evaluate.
7. If the antibacterial is not doing anything, switch to or add an anti-fungal ointment. Any over-the-counter antifungal used for humans will work, such as that for athlete’s foot or ‘jock itch’. Use for a week like steps #5 and 6 above.
8. Contrinue treatment until the plastron is smooth, dry, odor-free, and shows no
   signs of discharge. 
9. If

   it does not help, see a vet or other expert.

Outcomes

Most
forms of shell rot, caught early and treated aggressively, should be OK
although it may take months or even years for some of the shell damage
to fully heal and there may always be scars.

Resources

• Mader, Douglas R., DVM, ed. Reptile Medicine and Surgery. Saunders Elsevier, 2nd Edition 2006. ISBN 072169327X, pp. 697-698 and 895-896]

Edited 2-25-2013 (C) Mark Adkins