A novel virus, designated swine hepatitis E virus (swine HEV), was identified in pigs. Swine HEV crossreacts with antibody to the human HEV capsid antigen. Swine HEV is a ubiquitous agent and the majority of swine >3 months of age in herds from the midwestern United States were seropositive. Young pigs naturally infected by swine HEV were clinically normal but had microscopic evidence of hepatitis, and developed viremia prior to seroconversion. The entire ORFs 2 and 3 were amplified by reverse transcription-PCR from sera of naturally infected pigs. The putative capsid gene (ORF2) of swine HEV shared about 79-80% sequence identity at the nucleotide level and 90-92% identity at the amino acid level with human HEV strains. The small ORF3 of swine HEV had 83-85% nucleotide sequence identity and 77-82% amino acid identity with human HEV strains. Phylogenetic analyses showed that swine HEV is closely related to, but distinct from, human HEV strains. The discovery of swine HEV not only has implications for HEV vaccine development, diagnosis, and biology, but also raises a potential public health concern for zoonosis or xenozoonosis following xenotransplantation with pig organs.

Viral clearance during hepatitis B virus (HBV) infection has been thought to reflect the destruction of infected hepatocytes by CD8(+) T lymphocytes. However, in this study, HBV DNA was shown to largely disappear from the liver and the blood of acutely infected chimpanzees long before the peak of T cell infiltration and most of the liver disease. These results demonstrate that noncytopathic antiviral mechanisms contribute to viral clearance during acute viral hepatitis by purging HBV replicative intermediates from the cytoplasm and covalently closed circular viral DNA from the nucleus of infected cells.

Although the CD4؉ -and CD8 ؉ -T-cell responses to the hepatitis B virus (HBV) are thought to be crucial for the control of HBV infection, the relative contribution of each T-cell subset as an effector of viral clearance is not known. To examine this question, we monitored the course of HBV infection in control, CD4-depleted, and CD8-depleted chimpanzees. Our results demonstrate that CD8؉ cells are the main effector cells responsible for viral clearance and disease pathogenesis during acute HBV infection, and they suggest that viral clearance is mediated by both noncytolytic and cytolytic effector functions of the CD8؉ -T-cell response.

The mechanisms by which hepatitis C virus (HCV) induces chronic infection in the vast majority of infected individuals are unknown. Sequences within the HCV E1 and E2 envelope genes were analyzed during the acute phase of hepatitis C in 12 patients with different clinical outcomes. Acute resolving hepatitis was associated with relative evolutionary stasis of the heterogeneous viral population (quasispecies), whereas progressing hepatitis correlated with genetic evolution of HCV. Consistent with the hypothesis of selective pressure by the host immune system, the sequence changes occurred almost exclusively within the hypervariable region 1 of the E2 gene and were temporally correlated with antibody seroconversion. These data indicate that the evolutionary dynamics of the HCV quasispecies during the acute phase of hepatitis C predict whether the infection will resolve or become chronic.

To clarify the relationship between hepatitis C virus infection and the development of hepatocellular carcinoma as sequelae of non-A, non-B posttransfusion hepatitis, 231 patients with chronic non-A, non-B hepatitis (96 with chronic hepatitis, 81 with cirrhosis and 54 with hepatocellular carcinoma) were analyzed for antibody to hepatitis C virus and were compared with 125 patients with chronic hepatitis B (50 with chronic hepatitis, 46 with cirrhosis and 29 with hepatocellular carcinoma). Antibody to hepatitis C virus was detected in 89.6%, 86.4% and 94.4% of patients with non-A, non-B hepatitis-related chronic hepatitis, cirrhosis and hepatocellular carcinoma, respectively, compared with 6%, 17.4% and 34.5% with similar diseases related to hepatitis B. A history of transfusion was documented in 52%, 33% and 42% of anti-hepatitis C virus-positive cases of chronic hepatitis, cirrhosis and hepatocellular carcinoma. The mean intervals between the date of transfusion and the date of diagnosis of anti-hepatitis C virus-positive chronic hepatitis, cirrhosis and hepatocellular carcinoma were 10, 21.2 and 29 yr, respectively. In 21 patients with transfusion-associated hepatocellular carcinoma, anti-hepatitis C virus was present in each serial sample available for testing, including samples obtained up to 14 yr before the diagnosis of hepatocellular carcinoma. These data suggest the slow, sequential progression from acute hepatitis C virus-related non-A, non-B hepatitis through chronic hepatitis and cirrhosis to hepatocellular carcinoma and support a causal association between hepatitis C virus and hepatocellular carcinoma.

No abstract

Previous studies in hepatitis B virus (HBV)-infected humans and chimpanzees suggest that control of HBV infection involves the cells, effector functions, and molecular mediators of the immune response. The objective of the current study was to identify, in the liver of acutely HBV-infected chimpanzees, the spectrum of virusinduced and immune response-related genes that regulate the infection. The results demonstrate that HBV does not induce any genes during entry and expansion, suggesting it is a stealth virus early in the infection. In contrast, a large number of T cell-derived IFN-␥-regulated genes are induced in the liver during viral clearance, reflecting the impact of an adaptive T cell response that inhibits viral replication and kills infected cells, thereby terminating the infection.

This contribution is part of the special series of Inaugural Articles by members of the National Academy of Sciences elected on April 30, 2002. To define the early events that determine the outcome of acute hepatitis C virus (HCV) infection, we compared the course of viremia with the peripheral and intrahepatic T cell response and intrahepatic cytokine profile in six acutely infected chimpanzees. Three different outcomes were observed after peak viral titers were reached: sustained viral clearance, transient viral clearance followed by chronic infection, and chronic infection that persisted at initial peak titers. The results indicate that HCV spread outpaces the T cell response and that HCV rapidly induces but is not controlled by IFN-␣͞␤; that viral clearance follows the entry and accumulation of HCV-specific IFN-␥-producing T cells in the liver; and that it may not require the destruction of infected cells.