Use of and interpretation of results using inocula of hepatitis B virus with known infectivity titers.

The infectivity of three inocula (subtypes ayw, adr, and adw) of hepatitis B virus was evaluated by intravenous inoculation of 54 chimpanzees. End-point infectivity titers were 10(-7.5) (ayw), 10(-8.0) (adr), and 10(-7.0) (adw). In contrast, the end-point titers for detection of hepatitis B surface antigen by radioimmunoassay were 10(-4) (ayw), 10(-4) (adr), and 10(-5) (adw). The mean incubation period for infections transmitted by each dilution of each of the inocula was inversely proportional to the amount of infectious virus in the dilution, but substantial overlap was observed among proximate dilutions. The severity of hepatitis in the chimpanzees differed among the inocula, but it was unrelated to the amount of virus inoculated. Thus, conclusions about the infectivity of hepatitis B virus after inactivation based on titers of hepatitis B surface antigen or on the inverse relationship between the incubation period and the end-point infectivity titer must be made with caution.