A herpes virus, hence the name.
Sex. Although data to support spread by heterosexual sex (PubMed) or blood transfusion is negative.
Kaposi's sarcoma, body cavity lymphomas and angiofollicular lymph node hyperplasia (aka Castleman's disease). Castlemans, while occuring mostly in AIDS, can occur in those without HIV (PubMed).
Pateints who receive blood stored less than 4 days that is HHV-8 positive had higher mortality; remember that association is not causation, but it is a curiosity that needs some 'splainin' (PubMed).
Send to your local oncologist.