Ah cat abscesses...
Ok...we all have a good laugh about this in vet medicine..discharge is not "pus-sy" but is more correctly described as "purulent."
This is one of the most common things I see in cats that spend any time outdoors. It’s also one of my personal favorite problems to treat. Some people find it a bit gross but popping a cat abscess is one of the most satisfying things to me. It’s a good thing too because you know there will be a successful outcome and you can immediately make the cat feel better.
These can appear a few days to a week or more after a bite or puncture wound. Most often it is another cat that has inflicted it. It’s often on the head/neck (the instigator!) or the tail/back (because they got it while running away).
Sometimes the owner will see a swelling or the abscess will have even opened up and drained at home (on the cat or the couch). Cat pus is quite smelly so this is generally not something the owner is too pleased about. Frankly I am not either..I hate it when I don’t get to drain it!
In any case, the cat can also come in for limping (if it happens on a leg), lethargy (many of these cats have a fever) or going off food.
If it’s not already open and draining, we open it up, flush it out and let it heal. Sometimes, depending on where it is and how big it is, I may put a drain in it to keep it open for a few days. Cats are tremendous healers and sometimes they seal up too quickly! They need a rabies booster (any bite of unknown origin warrants this) and antibiotics. Even in cases where large amounts of skin are lost, these cats will heal! Sometimes it just takes a bit longer for the area to granulate in and close.
The other concern is that these cats are at risk for contracting Feline Immunodeficiency Virus (FIV) so they should be tested periodically if they go out and get into fights.
Here's a cool link to a vet website that shows in a series of photos the draining of a nasty (or for me, AWESOME!) abscess: Be Warned - for some this may be gross!