Cat soiling

Question
Hi Tina...I have three adorable cats that I rescued..one 9 years ago and two 8 years ago.  I've never had a problem with any of them until recently.  One avoids the litter box and will only go on a rug.  I removed the one rug and placed a litter box there.  It worked and after about a week I slowly began to move the litter box a foot or so until it was with the other litter boxes (I have three and clean them twice a day).  She has found the bathroom rug now and uses it (the bathroom is about 10 feet from the litter box).  The stool is well formed (not diarrhea or "hard" pellet like) and he or she (although I think it's one of the females) will occasionally urinate there as well.
Any suggestions as to how I can re-train her?  I've changed the litter types (scented, unscented, clumping, non-clumping..the full range) and am now out of ideas.  I even tried reasoning with her...well, you can imagine how far that got me :)
Anyway, any suggestions would be very very appreciated.
Thanks in advance for your help.
Anna Maria

Answer
HI Anna Maria,

Cats as you know are generally very clean and they do not start soiling their home without good reason. The first thing you need to do is bring a fresh stool sample from both cats to the vet and have them checked for internal parasites including worms, giardia, and coccidia. Irritation from worms is a frequent cause for cats defecating outside the box. Make sure you specify to the vet the reason you are having the fecal test done - there are certain species of worms more likely to cause irritation leading to this problem, and the vet can particularly watch for those.

If parasites are ruled out, it could be a behavioral problem - possible factors are changes or stress in her life, bullying fro one of the other cats, etc. You should always have at least one litter box per cat, preferably in separate locations so it's less likely for a bully to stake out the litter box and keep her away from it or ambush her as she leaves it.

Here are some tips on dealing with the problem (even if worms are treated, you need to thoroughly clean the scent even washing doesn't remove and may need to use some behavioral techniques to help her re-learn good habits).

http://catnet.stanford.edu/articles/litterbox.html