Hepatitis--which just means inflammation of the liver--can be caused by three different sexually transmitted viruses.
Hepatitis A is transmitted during rimming--so it's transmitted butt to mouth. You can get a vaccine to prevent Hepatitis A, which all men who have sex with men should definitely get.
Hepatitis B is transmitted just like HIV--through cum and blood. You can can a vaccine to prevent Hepatitis B, which all men who have sex with men should definitely get. Hep B can be prevented by using condoms.
Hepatitis C is transmitted primarily through blood--IV drug use and blood transfusions.
There are vaccinations to prevent Hepatitis A & B that all men who have sex with men should definitely get.
Using condoms can protect you from Hepatitis B and using a dental dam during rimming can protect you from Hepatitis A.
Read more about Hepatitis: HEPATITIS