mc7

Unfortunately the only virus that is routinely seriously (DNA) tested for is HIV. Other viral STDs are almost always just detected visually. But they don't display symptoms immediately or necessarily at all. So it's common and easy to not detect them even if present (until or unless they display symptoms). Also most other tests done (like urine tests) are not the more sensitive DNA tests but just cultures. These will only detect bacteria above a threshold. So there are these latent STD issues that exist.

But it's also possible that his problem is just a result of irritation? Irritation can also encourage yeast infections. These symptoms could just be a digestive yeast infection. (Cranberry and probiotics help overcome yeast.) Yeast are a major cause of anal fissures too (another thing this might be).

He should see a doctor since this has been going on so long. There are also some more serious things this could indicate... and probably a lot of things I don't know anything about. Hopefully it's just yeast and fixed easily.