This is a list of the skills that Erhard has, as well as the diseases he's learned to cure, both in canon and in various comms/RPs.

Skills

Diseases He Can Treat

Canon

Rosalia Virus

Able to make the cure/antiserum, as well as treat the initial bruising and foci colonies inside. Cannot treat the tumors in the bones or spinal colonies (that treatment is given to Hank Freebird).

GUILT, Post-GUILT Syndrome, & Neo-GUILT

As shown in his game, Erhard is in contact with Derek Stiles. Being that Erhard is a genuine surgeon, it's extremely unlikely that they wouldn't see him trained in treatments, just in case something happened or it reappeared.

RPs

White Chlorination Syndrome [Canon Page]

Discussed with Tyrann. He's working on treatments with what he can study from Kaine, Tyrann himself, and Nier.