More than 40 years after the discovery of human sapovirus (HuSaV), we have established a HuSaV culture system in which HuTu80 cells derived from the human duodenum adenocarcinoma cell line are cultured together with the addition of bile acid as a supplement. In addition to being a common cell line, this system using HuTu80 cells is a versatile method because classical culture media are available, and it is easy to scale-up for culture. However, the number of culture days required to obtain sufficient viral titer, the confirmation of viral gene conservation for sample selection, and the method for passaging of HuTu80-cells were crucial. So far, 15 genotypes have been successfully propagated and stocked, and stable supply as research resources has been achieved. Due to the above efforts, we can now proceed with the production and analysis of antisera using purified antigens and the evaluation of inactivation conditions. This manuscript introduces the background for selection of the cell line and bile acids, and the topics that have been discussed since the publication, as well as future issues that were raised such as the expression of cytopathicity and elucidation of low UV-C sensitivity of fecal-derived HuSaV.

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Human norovirus (HuNoV) is an infectious virus that accounts for more than half of all cases of infectious gastroenteritis, but its mechanism of infection and multiplication within the host are largely unknown. Accordingly, there are no available vaccines or specific therapeutic agents　applicable to HuNoV infection. The primary reason for this is the absence of an established in vitro culture and growth system for HuNoV. Therefore, virological analysis of HuNoV has been conducted using murine norovirus, which is most closely related to HuNoV and can be cultured in some cell-lines. Recently, several laboratories have reported successful in vitro cultivation of HuNoV using human intestinal epithelial cells, raising expectations for further advancements in HuNoV research. In this paper, we present recent findings regarding the in vitro propagation system of HuNoV.  

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Noroviruses are the most common viral cause of acute gastroenteritis after the introduction of rotavirus vaccines. Norovirus infection can cause severe symptoms in vulnerable populations including young children and the elderly. Thus, it is still a leading cause of death from diarrhea in children in developing countries. Recent advancement of genomics platforms facilitated understanding of the epidemiology of norovirus, while the whole picture of norovirus diversity is still undetermined. Currently, there are no approved vaccines for norovirus, but state-of-the-art norovirus cultivation systems could elucidate the antigenic diversity of this fast-evolving virus. In this review, we will summarize the historical and latest findings of norovirus epidemiology, diversity, and evolution.

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Rotavirus is a major cause of gastroenteritis in infants and is widely prevalent throughout the world regardless of the hygienic environment. However, it is not easy to understand the overall picture of rotavirus epidemic because of the great variety of genotypes and the large inter-seasonal and regional differences in the prevalent strains. Fortunately, the rotavirus vaccines now widely used around the world are highly effective and safe. The number of rotavirus gastroenteritis cases is declining dramatically, especially in high-income countries. In Japan, rotavirus vaccines have been included in the routine vaccination program since October 2020. Additionally, the impact of the SARS-CoV-2 pandemic control measures on the rotavirus epidemic was also very significant. These synergistic effects have resulted in few rotavirus outbreaks in recent years. Nevertheless, rotavirus is unlikely to be completely eradicated, and indeed a small number of sporadic cases continue to be reported. It will continue to be important to maintain high vaccination coverage and to continuously investigate prevalent strains. This review will provide an overview of the rotavirus epidemic situation in Japan and abroad. Annual changes in domestic epidemic strains that have been revealed by steady research to date will also be presented.

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[in Japanese]

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Measles virus (MeV), the causative agent of measles, can persist in the brain and cause a fatal neurodegenerative disease, subacute sclerosing panencephalitis (SSPE). Because wild-type MeV is not neurotropic, the virus is thought to evolve and acquire neuropathogenicity to cause SSPE. Our recent studies have shown that MeV acquires hyperfusogenic mutations in the fusion (F) gene that confer the ability to use cell adhesion molecule 1 (CADM1) and CADM2 as cis-acting receptor mimicking molecules and allow MeV to spread in neurons. Furthermore, under these conditions, multiple MeV genomes, rather than a single one, are likely to be transmitted transsynaptically between neurons through cell-cell fusion. Therefore, F proteins encoded by different genomes are co-expressed in infected cells, and positive and negative functional interactions between them can occur. These interactions determine the ability of the virus to spread in neurons as a population. In this article, we describe our studies to understand the mechanism by which MeV acquires neuropathogenicity in SSPE.

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Since the identification of severe fever with thrombocytopenia syndrome (SFTS) and its pathogen, a tick-borne bunyavirus, SFTS virus, there has been increasing interest in emerging viral infections caused by previously unknown viruses in ticks. This study aims to develop a comprehensive detection method for tick-borne bunyaviruses, conduct genetic analysis, isolate the detected viruses, and perform biological characterization. Through these studies, novel tick-borne bunyaviruses that have caused or may cause emerging infectious diseases were discovered. Tick-borne infections often occur sporadically, making their occurrence difficult to recognize. Therefore, continuous exploration of viruses in ticks and assessment of their potential risks causing human and animal diseases is required.

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