If this had been a warble or some other type of fly, the maggot would have been easy to see in the wound when it was opened up. It's tricky work getting one of those things out; if you break them during the removal process, the toxins released can kill the rabbit.
Myxomatosis is a serious, most often fatal, disease; an animal infected with it wouldn't have just one lump.
Most likely, this was a small abscess. An abscess can occur any time a break in the skin allows bacteria to get beneath the surface, but sometimes they seem to occur spontaneously without an injury having ever been seen. Rabbits usually have a remarkable ability to wall off infection, but sometimes their immune systems get overwhelmed and what started as one abscess can turn into a big mess. I'm glad to hear that this one cleared up so fast and so well.
Myxomatosis is a serious, most often fatal, disease; an animal infected with it wouldn't have just one lump.
Most likely, this was a small abscess. An abscess can occur any time a break in the skin allows bacteria to get beneath the surface, but sometimes they seem to occur spontaneously without an injury having ever been seen. Rabbits usually have a remarkable ability to wall off infection, but sometimes their immune systems get overwhelmed and what started as one abscess can turn into a big mess. I'm glad to hear that this one cleared up so fast and so well.
