Masaaki Mizui

Sex- and Age-Specific Carriers of Hepatitis B and C Viruses in Japan Estimated by the Prevalence in the 3,485,648 First-Time Blood Donors during 1995–2000

Objective: Carriers of hepatitis B virus (HBV) and hepatitis C virus (HCV) in Japan were estimated on a national basis. Methods: Sera from the first-time blood donors aged 16–64 years in eight jurisdictions of the Japanese Red Cross Blood Center during 1995–2000 were tested for hepatitis B surface antigen (HBsAg) and antibody to HCV (anti-HCV). Viremia with HCV was estimated to be present in 70% of donors with anti-HCV. Results: HBsAg was detected in 22,018 of 3,485,648 (0.63%) blood donors including 12,990 of 1,780,149 (0.73%) men and 9,028 of 1,705,499 (0.53%) women, and anti-HCV in 17,010 (0.49%) including 8,504 (0.48%) men and 8,506 (0.50%) women. Multiplying the carrier rate by the population registered in the Census 2000, the total HBV carriers aged 15–65 years were estimated at 967,753 (95% confidence interval 806,760–1,128,745), of whom 571,210 (479,267–663,152) were men and 396,543 (327,494–465,593) were women. Likewise, the total HCV carriers were estimated at 884,954 (95% confidence interval 725,082–1,044,826), of whom 464,363 (377,927–550,799) were men and 420,591 (347,156–494,027) were women. Conclusion: Estimated numbers of HBV and HCV carriers would help plan to prevent the development of hepatocellular carcinoma in Japan.

Total numbers of undiagnosed carriers of hepatitis C and B viruses in Japan estimated by age- and area-specific prevalence on the national scale.

Objective: To estimate total numbers of undiagnosed carriers of hepatitis C virus (HCV) and hepatitis B virus (HBV) in Japan. Methods: Area- and age-specific prevalence of HCV as well as HBV was determined in the first-time blood donors [20–39 years (n = 2,429,364)] and examinees of periodical health check-ups [40–74 years (6,204,968 for HCV and 6,228,967 for HBV)] in Japan. Prevalence in adolescents [5–19 years (79,256 for HCV and 68,792 for HBV)] was determined in a single prefecture, and that of HCV in the elderly (≧75 years) was estimated by the exponential model. HBV infection was determined by the detection of hepatitis B surface antigen, and HCV infection by either the algorithm or assuming persistent infection in 70% of the individuals with antibody to HCV. Results: Of the total population of 127,285,653 in 2005, 807,903 (95% CI 679,886–974,292) were estimated to be infected with HCV at a carrier rate of 0.63%, and 903,145 (837,189–969,572) with HBV at that of 0.71%. Conclusion: Accurate estimation of undiagnosed HCV and HBV carriers in the general population would help to predict the future burden of liver disease, and take appropriate measures for improving healthcare.

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.

Incidence rates of hepatitis B and C virus infections among blood donors in Hiroshima, Japan, during 10 years from 1994 to 2004.

Objective: Although prevalence rates of hepatitis B virus (HBV) and hepatitis C virus (HCV) infections have kept decreasing in blood donors, there is little information on incidence rates of these hepatitis viruses in Japan. Methods: During 10 years from June 1994 through April 2004, 418,269 inhabitants of Hiroshima, Japan, donated blood (1,409,465 units in total). They were screened for serum markers of HBV and HCV infections, and individuals who developed de novo infections were identified. Results: Infection with HBV occurred at a rate of 2.78 per 100,000 person-years (95% confidence interval: 1.78–4.14/100,000 person-years) and that with HCV at a rate of 1.86 per 100,000 person-years (95% confidence interval: 1.06–3.01/100,000 person-years). Residual risks of transmission by transfusions, based on the relationship risk [window period (estimated at 0.15 and 0.03 years in chimpanzees inoculated with minimum infectious doses for HBV and HCV, respectively) × incidence], were 1/243,000 for HBV and 1/1,960,000 for HCV infections. Conclusion: At present, incidence rates of HBV and HCV infections are extremely low in Japan.

Liver disease in hepatitis C virus carriers identified at blood donation and their outcomes with or without interferon treatment: Study on 1019 carriers followed for 5-10 years.

Aim:  To portray liver disease and project outcomes in carriers of hepatitis C virus (HCV) in the general population.

Lack of Epidemiological Evidence for a Role of Resolved Hepatitis B Virus Infection in Hepatocarcinogenesis in Patients Infected with Hepatitis C Virus in Japan

Objective: The role of resolved hepatitis B virus (HBV) infection in promoting hepatocellular carcinoma (HCC) in patients infected with hepatitis C virus (HCV) in Japan was evaluated by epidemiological surveys. Methods: Antibody to hepatitis B core (anti-HBc) was determined in age-matched blood donors, and the frequency was compared with that in patients with HCV-associated HCC in Japan. Results: Anti-HBc was detected significantly more frequently in the blood donors with than without antibody to HCV (anti-HCV; 76/135 or 56.3% vs. 65/255 or 25.5%, p < 0.001). In the patients with HCV-associated HCC, anti-HBc was detected in 109 of 202 (54.0%), which was comparable to the frequency in anti-HCV-positive blood donors (56.3%). Among the blood donors with anti-HCV, the prevalence of anti-HBc was no different between those with and without HCV RNA in serum (40/77 or 51.9% vs. 36/58 or 62.1%). Conclusions: The individuals of an age with high cancer frequency (≧40 years) in Japan would have been exposed to HBV frequently (>50%), whether or not they have developed HCV-associated HCC. Despite repeated assertions in the literature, no epidemiological evidence was obtained for a role of past HBV infection in hepatocarcinogenesis in patients infected with HCV in Japan.

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.

Comparison of HCV core antigen activity by ELISA and amount of HCV RNA by branched DNA assay

Recently an assay system for direct detection of HCV RNA using a branched DNA probe (branched DNA assay: bDNA assay) has been developed for practical use. Concurrently, a method for direct quantitation of HCV particles by measurement of serum HCV core antigen activity has also been established. We compared the results of serum HCV RNA quantitation by bDNA assay and HCV core antigen measurements, and found a highly significant correlation between the two methods (R2 = 0.816).