Some clinical reports and epidemiological data suggest that a virus may play a role in the etiology of Parkinson's disease (PD). Once a certain strain of influenza A virus has adapted to the central nervous system, it will gain infectivity to neurons, especially in the substantia nigra, cerebellum and hippocampus, both in human cases and experimental models. Although efforts to detect virus particles in the brains, or antibodies in the serum or cerebrospinal fluid of patients with PD have been generally unsuccessful, recent immunohistochemical work has revealed the presence of complement proteins and the interferon induced MxA in association with Lewy bodies and swollen neuronal process. We propose a hypothesis that neurovirulent influenza A virus and other potent viruses may be responsible for the formation of Lewy bodies and the later death of nigral neurons, to constitute a viral etiology for PD.

Some patients developed Guillain-Barré syndrome (GBS) after the administration of bovine gangliosides. Patients with GBS subsequent to Campylobacter jejuni enteritis frequently have IgG antibody to GM1 ganglioside. Miller Fisher syndrome (MFS), a variant of GBS, is associated with IgG antibody to GQ1b ganglioside. We showed the existence of molecular mimicry between GM1 and lipopolysaccharide of C. jejuni isolated from patients with GBS, and that between GQ1b and C. jejuni lipopolysaccharides from patients with MFS. The molecular mimicry between infectious agents and gangliosides may function in the production of anti-ganglioside antibodies. This sugar mimicry is one possible cause for GBS and MFS, and unidentified host factor may contribute to the development of these syndromes.

The possible involvement of retroviruses in the development of autoimmune diseases has long been discussed. Exogenous retroviral infections and aberrant endogenous retroviral expressions can possibly induce immune dysfunction directly or indirectly. In addition to observations of autoimmune disease-like features in animal models, indirect evidences implicating retroviruses in human autoimmune diseases have been shown in a number of reports. However, direct evidence for the etiologic role of retroviruses in human autoimmune diseases has not yet been obtained.

Epstein-Barr virus (EBV) infection is found in 7% of Japanese gastric carcinoma. Our strategy is to establish the EBV infected epithelial cell lines from EBV infected gastric carcinomas and to characterize the cell lines on the bases of cellular and molecular biology to define the etiological role of EBV. We have characterized two EBV positive cell lines, GT38 and GT39 from gastric tissues. The both cell lines were EBV latency type III and produced the virus spontaneously. The character of tumor cells was demonstrated by the colony formation in soft agar and the tumorigenesis in severe combined immunodeficient mice.

The hepatitis C virus (HCV) infection is associated with a wide spectrum of clinical entities ranging from asymptomatic carriage to severe forms of chronic hepatitis. In Egypt, HCV infection has been shown to be highly prevalent. The aim of this study was to determine the frequency and significance of anti-HCV IgM in the sera of clinically healthy blood donors and chronic HCV patients, whose sera were also positive for anti-HCV IgG. Anti-HCV IgM was detected in the sera of 7 (46%) of the blood donors (n=15), of whom 5 (71%) had a positive HCV-RNA. The corresponding results in patients with a chronic hepatitis C (CHC) infection (n=19) were 8 (42%) and 5 (62%), respectively. The detection of anti-HCV IgM did not correlate with a positive test for HCV-RNA (R=0.2) in the CHC patients. However, the levels of anti-HCV IgM in CHC patients were associated significantly with the level of serum transaminase, a finding that can be used in monitoring disease activity in such a group of patients. On the other hand, a significant association was evident between the detection of anti-HCV IgM and HCV-RNA in the sera of blood donors. Thus among the blood donors, viraemia correlates well with the detection of HCV-IgM Ab, but it cannot be excluded in its absence. The presence of HCV-IgM in some patients with CHC infection indicates that the antibody as a viral marker may not be unique to acute HCV infection.

We investigated chronological and geographical changes of alveolar echinococcosis (AE) prevalence in 14 administrative districts of Hokkaido based on the data of our epizootiologic and seroepidemiologic surveys. The results suggest that the chronological transitions of the enzootic state of AE in Hokkaido markedly reflect those of human AE prevalence, and that new prevalence of human AE has been emerging from central and western Hokkaido.

The prevalence of antibodies against hepatitis C virus (HCV) and the distribution pattern of HCV subtypes were analyzed among healthy blood donors and intravenous drug users (IVDUs) in northern/northeastern Thailand. The prevalence of anti-HCV antibodies was 3.2% (26/820) among blood donors in Khon Kaen, while it was 90% (71/79) among IVDUs in Chiang Rai. HCV RNA was detected in all anti-HCV-positive sera collected from blood donors and IVDUs tested, as determined by reverse transcription-PCR analysis. Sequence analyses of amplified fragments of the HCV genome revealed that in Khon Kaen and Chiang Rai, Thailand, HCV-3a (50-60%) was the most common HCV subtype, followed by HCV-1a, HCV-1b, and subtypes of clade 6, each at 10-20%.

A total of 297 strains of Vibrio fluvialis and Vibrio furnissii, which were collected from various countries for the past 15-year period of 1984-1998, were serogrouped. Of those examined, 239 strains of V.fluvialis and V.furnissii were classified into 29 known O serogroups; 9 strains were found to belong to R-form cultures, and the rest of the 49 strains could not be serogrouped. Of those serologically untypable strains, 26 novel O serogroups (O36 to O61) were established and added to our reference of the V.fluvialis and V.furnissii antigenic scheme. As all antisera against the O reference strains of the organisms contained some amount of antibody to the rough (R) antigen, all diagnostic O antisera were absorbed with the reference rough strain, V.fluvialis GF25.