Waterborne pathogenic viruses, such as noroviruses, cause acute gastroenteritis or hepatitis to humans. Also, human infection with highly pathogenic avian influenza A (H5N1) virus is of a great public health concern in the world, and the H5N1 avian influenza is one of the important emerging diseases for humans. This study aimed to obtain systematic and comprehensive knowledge to control human infections caused by the pathogenic viruses. Specific topics are described below.

I. Molecular epidemiological analysis of pathogenic viruses in water environments^{1, 2, 4, 5, 6, 7, 9)}
The prevalence and genetic diversity of gastroenteritis viruses, noroviruses, sapoviruses, and Aichi viruses, in wastewater and river water were investigated during a 1-year period. This study revealed that genetically diverse strains are circulating between human populations and water environments. Molecular detection and characterization of human gastroenteritis viruses in wastewater and river water enable us to identify the circulating strains, including those shed by sporadic, mild, or asymptomatic patients in a given treatment service area.

II. Chlorine inactivation of norovirus in drinking water³⁾
Inactivation of human noroviruses by chlorine disinfection has not been well characterized because of the absence of routine in vitro infectivity assay systems. In this study, cultivable murine norovirus was used as a surrogate to evaluate resistance of human noroviruses to chlorination in drinking water supply system. It was demonstrated that appropriate water treatment process with chlorination could manage the risk of norovirus infection via drinking water supply systems.

III. Quantitative risk assessment of highly pathogenic avian influenza A (H5N1) virus infections⁸⁾
Infection risk of the H5N1 virus was quantitatively evaluated, and a time-dose-response model to describe mortality of mice exposed to an H5N1 virus, describing the mortality over time and represents experimental responses accurately, was successfully developed. The models developed in this study will be useful to evaluate the risks of H5N1 virus infection under various exposure scenarios and to estimate the mortality of H5N1 virus.

I was awarded the following prizes for my work described above: "Ikushi Prize by Japan Society for the Promotion of Science (JSPS)", "Japan Society on Water Environment (JSWE) President's Award", "The University of Tokyo President's Award", and "IWA-HRWM Willie Grabow Young Investigator Award", etc.