Acute hepatitis D virus (HDV or Delta virus)

Structure:

Is an incomplete RNA particle enclosed in a shell of HBsAg

It is unable to replicate by itself, but is activated by the presence of HBV

Co-infection with HBV:

Is clinically indistinguishable from an acute icteric HBV infection

Diagnosis is confirmed by finding:

Serum IgM anti-δ + IgM anti-HBc

Super-infection:

Results in an acute flare-up of previously quiescent chronic HBV infection

A rise in serum AST or ALT may be the only indication of infection

Diagnosis is confirmed by finding:

Serum IgM anti-δ + IgG anti-HBc

Fulminant hepatitis can follow both types of infection, but is more common after co-infection.