(West Augusta, VA)
There is an outside barn cat about a year old that has developed redness and swelling of the testicles and anus. I am pretty sure there is diarrhea, too.
I can probably catch him, but the cat has never had any vaccinations.
Any guess about how serious this is?
The irritation that you see could be from a number of things. The kitty could have diarrhea from intestinal parasites, causing the skin on his rear end to be inflamed from the diarrhea.
Of course, he could also be having an allergic reaction to something, most often fleas. Flea bite dermatitis can become quite severe and it would be quite likely that he has fleas since he is living outdoors and in a barn.
Outdoor cats are also more prone to viruses such as Feline Leukemia and Feline Immunodeficiency Virus. Both viruses depress the immune system and thus the affected cats are more prone to infection of any kind.
Cats in that situation also commonly fight with other cats and he could have a bite wound that has become infected, including an abscess in the testicles.
Intact male cats also can develop testicular cancer which could make the area look red and irritated.
As you can see, there are many different possible causes of his condition. I have only listed a few. There are others. The only way to know what is bothering him is to have him examined by a veterinarian.
If you want to help him and can get him into a carrier, he definitely needs to be taken to the vet. If you can't handle him and get him into a carrier, perhaps you could borrow a humane trap and catch him in it and then take him straight to the vet. He needs to be examined in general, but also specifically for worms, fleas, infections, as well as have a Feline Leukemia/FIV blood test. He should also receive vaccines if he is healthy enough and be neutered.
Good Luck. I hope you can help him.