Titration of the infectivity of hepatitis D virus in chimpanzees.

The infectivity of hepatitis D virus (HDV) was evaluated by intravenous inoculation of chimpanzees. HDV was present in the inoculum at a titer of 10(11) chimpanzee infectious doses (CID). In contrast, the titer of hepatitis B virus (HBV) in the same inoculum was 10(6) CID. All HBV-infected chimpanzees inoculated with less than or equal to 10(-11) dilutions of the HDV-positive plasma were superinfected; an animal receiving a 10(-12) dilution did not develop markers of HDV replication in serum or liver. All HDV-infected chimpanzees had marked elevations of serum alanine aminotransferase activities. The incubation period from exposure to development of hepatitis was inversely related to the dose of HDV inoculum, although the severity and duration of hepatitis were independent of it. All animals recovered and rapidly developed antibody to hepatitis D antigen.