Characterization of anti-idiotypic antibodies mimicking antibody- and receptor-binding sites on hepatitis A virus.

Two anti-idiotypic monoclonal antibodies (mAb2s; named 94-2 and 94-7), were generated from a BALB/c mouse immunized with human monoclonal anti-hepatitis A virus (HAV) neutralizing antibody KF94. We characterized the properties of the mAb2s and determined interactions between mAb2s, KF94 and HAV using enzyme-linked immunosorbent assay, immunofluorescence assay and HAV infectivity assay. Inactivated HAV inhibited mAb2 binding to KF94, indicating that the mAb2s mimicked the HAV neutralization site that was complementary to the paratope of KF94. MAb2 94-7 competed with an anti-HAV cellular receptor antibody for binding to HAV-susceptible cells and partially blocked virus infection. We speculated that mAb2 94-7 mimicked a portion of the HAV receptor-binding site. The ability to generate mAb2 implies that HAV receptor-binding sites are exposed on the surface of HAV, permitting antibody access.

Rapid and real-time detection of hepatitis A virus by reverse transcription loop-mediated isothermal amplification assay.

A one-step, single tube, real-time reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay was developed for detecting sequences of the untranslated region in the genome of hepatitis A virus (HAV). The RT-LAMP assay reported in this study was very simple and rapid; the HAV-specific amplification was obtained in 50 min under isothermal conditions at 62.5 degrees C by employing a set of seven primers. The RNAs of three cell-adapted HAV strains belonging to different subgenotypes (IA, IB and IIIB) were equally well amplified. The detection limits of the RT-LAMP assay for these HAV strains were 0.4-0.8 focus forming units (FFU)/reaction. The results of the calibration using the WHO international standard indicated that the RT-LAMP assay had similar sensitivity to the conventional RT-PCR method. A comparison of the results from the RT-LAMP and the LightCycler PCR assay using clinical samples in feces revealed that the findings were similar between the two methods. Although several genotypes remain to be tested, it is concluded that the new real-time RT-LAMP assay is very suitable for detection and quantitation of most prevalent genotypes of HAV in diagnostic laboratories.

Shifting seroepidemiology of hepatitis A in Japan, 1973-2003.

BACKGROUND: Hepatitis A infection is caused by hepatitis A virus (HAV) contracted through fecal-oral transmission. Life-long immunity is conferred after infection. Improved sanitary conditions have generally resulted in a significant decline in the incidence of hepatitis A. However, a low incidence of infection results in increased HAV susceptibility. The present study investigates the prevalence of anti-HAV antibody and clarifies the current HAV status and HAV susceptibility in Japan at 2003. METHODS: A total of 2,430 serum specimens collected during 2003 from Japanese individuals ranging in age from 0-92 years, were tested for anti-HAV antibody using an inhibition enzyme linked immunosorbent assay. All specimens were obtained from the WHO and the National Serum Reference Bank/National Institute of Infectious Diseases, Tokyo, Japan. RESULTS: The overall seroprevalence was 12.2%. Anti-HAV antibodies were rarely detected in individuals between 0-44 years of age. Starting from the age of 45-49 years, seropositivity gradually increased through age 65 years and above. Seroprevalence was not affected by gender, and geographic distribution did not affect age-specific seroprevalence until the age of 60 years. CONCLUSIONS: HAV susceptibility in Japan is increasing annually. Particularly, the prevalence of anti-HAV antibody in individuals older than 50 years in 2003 was 50.3%, which is significantly lower than that of corresponding studies in 1994 (74.3%), 1984 (96.9%) and 1973 (96.9%). The growing susceptible population of advanced age results in more frequent HAV infection among them. The surveillance of anti-HAV antibody prevalence is useful for implementing preventive measures and for controlling the spread of HAV.

Outbreak of central nervous system disease associated with hand, foot, and mouth disease in Japan during the summer of 2000: detection and molecular epidemiology of enterovirus 71.

Few outbreaks of the serious enterovirus 71 (EV71) infections, which affect the central nervous system (CNS), had been reported in Japan before 2000. During June through August 2000, a patient died of pulmonary edema caused by brainstem encephalitis accompanied by EV71-induced hand, foot, and mouth disease (HFMD), and many patients complicated by serious CNS disease, including paralysis, were hospitalized in a restricted area in Hyogo Prefecture, Japan (K-area). During the same period, endemics of HFMD were reported in other areas in Hyogo Prefecture, where EV71 was isolated from HFMD patients, but few patients developed aseptic meningitis. The isolations of EV71 from K-area patients were difficult with the use of Vero cells, so the strains were isolated by use of GL37 cells; Vero cells, however, could isolate EV71 strains from other areas in Hyogo Prefecture. We sequenced VP4 coding regions of these EV71 isolates and found that the isolates from K-area had the same sequence, which, except for one isolate, was different from the sequences of EV71 strains isolated from other areas of Hyogo Prefecture. Although these results were not enough to state that EV71 from K-area was a virulent strain, it seemed reasonable to conclude that serious CNS diseases in K-area were caused by EV71 because it was the only infectious agent detected in the inpatients of K-area.