Hisao Yugi

Infectivity of blood components with low hepatitis B virus DNA levels identified in a lookback program

BACKGROUND: Japanese Red Cross (JRC) blood centers implemented anti‐hepatitis B core antigen (HBc) screening in 1989 and 50‐minipool (MP)‐nucleic acid testing (NAT) in 2000. A systematic lookback study has been conducted to determine the hepatitis B virus (HBV) transmission risk of donations drawn in the pre‐hepatitis B surface antigen (HBsAg) and/or MP‐NAT window phase and by donors with occult HBV infection.

Minimum infectious dose of hepatitis B virus in chimpanzees and difference in the dynamics of viremia between genotype A and genotype C

BACKGROUND: In planning optimal hepatitis B virus (HBV) blood screening strategies, the minimum infectious dose and early dynamics of HBV need to be determined for defining the window period for HBV DNA as well as for hepatitis B surface antigen (HBsAg).

Titration of hepatitis B virus infectivity in the sera of pre‐acute and late acute phases of HBV infection: Transmission experiments to chimeric mice with human liver repopulated hepatocytes

Studies of hepatitis B virus (HBV) infection in non‐human primates such as chimpanzees are no longer possible due to ethical considerations and the endangered status of chimpanzees since April 2007 in Japan. A human hepatocyte transplanted chimeric mouse was used to characterize HBV infectivity in serial stages of acute infection. Chimeric mice were inoculated intravenously with serum samples obtained from an experimentally infected chimpanzee with HBV. Sera from the pre‐acute phases (i.e., rump‐up viremia prior to anti‐HBc) and late acute phases (i.e., declining phase of HBsAg and anti‐HBcAb positive) were collected from the chimpanzees 57 and 244 days after inoculation. These sera contained 2.6 × 106 and 2.8 × 106 copies/ml of HBV DNA, respectively. Three chimeric mice inoculated intravenously with 100 µl of pre‐acute serum (equivalent to 100 copy of HBV DNA) developed an HBV infection. The three chimeric mice that received 100 µl of pre‐acute serum (equivalent to 101 copies of HBV DNA), developed high levels of serum HBV DNA. None of the three chimeric mice inoculated with 100 µl of 1:104 dilution (equivalent to 101 copies of HBV DNA) of late‐acute serum was infected, while only one of three chimeric mice inoculated with 100 µl of 1:103 dilution (equivalent to 102 copies of HBV DNA) of late‐acute serum developed an HBV infection. Based on these results, chimeric mice can be used as animal models for the study of HBV infectivity, pathogenesis and control. The results show that pre‐acute phase HBV serum is about 100‐times more infectious than late acute phase serum. J. Med. Virol. 80:2064–2068, 2008.

Titration of Hepatitis C Virus in Chimpanzees for Determining the Copy Number Required for Transmission

Objective: To determine the copy number of hepatitis C virus (HCV) RNA, determined by nucleic acid amplification test (NAT) for screening blood units in Japan, that can transmit infection to chimpanzees. Methods: Fresh-frozen plasma with markers of HCV infection, as well as inocula pedigreed from 1 of them, were evaluated for the infectious activity in chimpanzees. Results: One unit each (273–282 ml) of fresh-frozen plasma from 2 blood donors or a pool from 13 donors to make a unit, which contained high-titered antibody to HCV but without HCV RNA detectable by NAT, did not infect any of 3 chimpanzees. Two chimpanzees were infected, however, when they were inoculated with 1 ml of serum from a blood donor in the ‘window period’ of HCV infection and containing 7.0 × 106 copies/ml of HCV RNA. The preacute phase serum from 1 of them harvested 7 weeks after the inoculation was titrated in 2 chimpanzees, and an inoculum containing approximately 2 × 101 copies of HCV RNA could transmit infection to both of them. Conclusion: Approximately 20 copies of HCV can transmit infection to recipients, which needs to be taken into consideration in planning the screening of blood units for HCV RNA by NAT. Although the sensitivity of present NAT could be improved further, there would be a limit of it in detecting a low-level HCV RNA in the window period of donors with the infectious capacity in recipients.

Early Dynamics of Hepatitis C Virus in the Circulation of Chimpanzees with Experimental Infection

Two chimpanzees were inoculated with hepatitis C virus (HCV) and followed on a daily basis for 12 days. HCV RNA became detectable in their sera on day 5 by polymerase chain reaction with the detection limit of 102 copies/ml. Based on an exponential growth observed until 8 or 9 days after inoculation in their sera, the doubling time of HCV in the circulation was estimated at 6.3–8.6 h and log time (time required to grow 10-fold) at 31.3– 42.9 h. The exact doubling time of HCV determined in them would help plan an efficient strategy for screening out blood donors in the window period of infection between the exposure and the development of antibody to HCV in serum.

Interferon Alone or Combined with Ribavirin for Acute Prolonged Infection with Hepatitis C Virus in Chimpanzees

Infection with hepatitis C virus (HCV) persisted for longer than 29 weeks in 2 chimpanzees after they had been inoculated with it experimentally. One of them (C-210) received short-term subcutaneous interferon-α (IFN-α) 6 million units (MU) daily for 7 days at week 29. He cleared HCV RNA from the serum and remained negative for it during 25 weeks after the withdrawal of IFN. The other (C-224) did not respond to 2 courses of a short-term IFN monotherapy at weeks 20 and 23. Twelve weeks thereafter, he received IFN-α 3 MU daily for 2 weeks and then 3 times a week for 14 weeks combined with oral ribavirin 600 mg daily during 16 weeks. HCV RNA disappeared from the serum and stayed negative until the last follow-up 24 weeks after the completion of combination therapy.