Some plant viruses are transmitted to new host plants via pollen. However, since the first report of pollen transmission of plant viruses in 1918, the fundamental mechanisms underlying this process have remained unresolved. Pollen transmission of plant viruses is classified into two types: vertical transmission via pollen and horizontal transmission via pollen. Recently, we have obtained important insights into these mechanisms. In vertical transmission via pollen, it was suggested that when virus-infected pollen grains germinate, the pollen tubes deliver the sperm cells required for fertilization into the embryo sacs while simultaneously introducing the virus, resulting in the formation of virus-infected seeds. In contrast, in horizontal transmission via pollen, it was suggested that pollen tubes that have accumulated the virus penetrate and elongate within the stigma, establishing the initial virus infection sites. The infection then expanded into the vascular tissues of the stigma and style, and subsequently spread throughout the plant via the phloem. Thus, pollenborne viruses are thought to exploit the sexual reproduction system of seed plants, using pollen as a vector to achieve both horizontal and vertical transmission. In this review, we provide an overview of our research conducted to date on the transmission mechanisms of pollen-borne viruses.
More than 40 years have passed since human immunodeficiency virus (HIV), the causative agent of acquired immune deficiency syndrome (AIDS), was isolated in 1983. In the early days of the epidemic, AIDS was feared as a deadly disease, but today, thanks to advances in anti-retroviral drugs, many infected individuals can maintain their health as long as they take their medication. Furthermore, advances in basic research have clarified why HIV is difficult to eliminate from the body and how it causes immune deficiency in infected individuals. This paper outlines the progress made over the past 40 years in the following areas: the discovery of HIV, HIV denialism, receptors and co-receptors, biases in HIV isolation, broadly neutralizing antibodies, and understanding the pathogenesis of AIDS.
The COVID-19 pandemic has spurred vigorous research in a field that is old but new, a fusion of aerosol science and virology, each with its own history. I tentatively refer to this interdisciplinary field as "aerosol virology". This review article aims to convey the appeal of research in this field to virologists unfamiliar with aerosol science, covering fundamental knowledge of aerosols. In fact, preceding this article, I had published in the Japanese Journal of Aerosol Science a companion review with this, titled "An Introduction to Aerosol Virology"1）, which included basic virological knowledge for members less familiar with viruses, aiming to spark their interest in the field. To advance "aerosol virology", it is necessary to approach research goals with knowledge of both aerosol science and virology, not just one field. This represents a largely unexplored frontier even for virology. I hope members of the Virology Society will venture into this frontier. Both reviews were written with this aspiration in mind.
As of May 2025, measles outbreaks have been occurring worldwide. Japan has reported the highest number of cases since the beginning of the COVID-19. Unvaccinated measles cases are highly contagious and at high risk for serious illness, so it is important to ensure that children receive the live attenuated measles-rubella (MR) vaccine as soon as they become one year old. Additionally, the second routine immunization coverage rate must be raised to 95% or higher among five-to six- year-old children (one year before entering elementary school). For elementary school students and older individuals, it is important to check the vaccine records showing two doses of a measles-containing vaccine administered at or after one year of age. Those born on or after April 2, 1990, had the opportunity to receive two routine vaccinations; however, their records must be checked to confirm receipt. We also recommend checking vaccination records before traveling abroad. Additionally, rapid active epidemiological surveillance should be conducted in the event of a single measles case. Emergency vaccination within 72 hours of exposure for susceptible individuals may prevent the disease. For individuals ineligible for vaccination, health insurance covers the prevention of severe disease through an intramuscular injection of human immunoglobulin within six days of exposure. The most important measure is prophylaxis prior to exposure to the measles virus.
Many of the emerging and re-emerging viral diseases that have caused global outbreaks in recent years -such as severe acute respiratory syndrome (SARS), dengue fever, Zika virus disease, and COVID-19 -are caused by positive-sense single-stranded RNA (+ssRNA) viruses. This review focuses on members of the Flaviviridae family, a diverse group of +ssRNA viruses that exhibit distinct host and tissue tropisms, and summarizes our recent efforts to elucidate the molecular determinants underlying their pathogenicity and tropism. By refining reverse genetics systems that enable precise manipulation of viral genomes, we have uncovered the functional roles of specific viral proteins in pathogenesis through experimental infections using animal models that recapitulate disease phenotypes. In addition, by analyzing structural variations within viral genomes, we successfully identified key elements responsible for determining viral specificity. We have also developed innovative viral reporter assays that incorporate advanced imaging technologies, enabling real-time visualization of viral dynamics in vivo and facilitating diagnostic applications. This review integrates these findings to provide insights into how pathogenicity and tissue tropism evolve through repeated interspecies transmission, and discusses the potential of such approaches as a foundational platform for future infectious disease research and countermeasures.
Epstein-Barr virus (EBV), a member of the herpesvirus family, infects more than 90% of adults and establishes a lifelong latent infection. In addition to its involvement in a wide range of malignancies such as lymphomas, nasopharyngeal carcinoma, and gastric cancer, recent evidence has shown its potential association with autoimmune diseases, positioning EBV as an interdisciplinary research model linking virology, oncology, and immunology. Historically, EBV research has been hindered by technical limitations in viral culture systems and animal models. However, recent advances-including whole-genome cloning using bacterial artificial chromosomes (BACs), gene editing via CRISPR/Cas9, and the development of in vivo models such as humanized mice-have accelerated the elucidation of EBV' s unique life cycle and tumorigenic mechanisms. In this review, we discuss the evolution of techniques for generating recombinant EBVs and in vivo modeling, both essential for functional genetic analysis, and highlight our contributions to the advancement of these tools and their application in researching EBV-associated tumorigenesis.
HIV replication highly interacts with host immunity resulting in life-long persistent virus replication in the presence of adaptive immune responses. Development of an effective vaccine is a key for control of global HIV epidemic, but immunization methods to induce effective anti-HIV immune responses have not been established. We have been focusing on analyzing virus-host immune interaction in vivo using animal models and applying findings to the development of vaccines. We have developed a novel immunogen selectively inducing virus-specific CD8+ T-cell responses and showed protective efficacy of vaccines against intrarectal SIV challenge. We have also worked on antibody responses, and determined the polymorphism in germline immunoglobulin genes in macaques and its association with induction of a particular class of anti-SIV neutralizing antibody. We applied the knowledge in HIV research to HTLV and COVID-19, showing protective efficacy of vaccine-induced neutralizing antibody against HTLV infection and viral suppression by vaccine-induced CD8+ T-cell responses against SARS-CoV-2 in macaque models.
Measles virus is the pathogen that causes measles and is highly infectious. Measles virus uses two molecules as viral receptors: signaling lymphocytic activation molecule, expressed on immune cells, and nectin-4, expressed on epithelial cells. Usage of these receptors is strongly associated with the pathogenesis of measles. Although it remains a leading cause of childhood mortality worldwide, measles elimination is being promoted by the availability of a highly effective live attenuated vaccines. Due to the elimination of measles in many countries, the circulating measles genotypes have been reduced to two, B3 and D8, in recent years. Therefore, in addition to genotyping using the conventional 450-nucleotide N gene region, new methods such as wholegenome sequencing and analysis of the M-F non-coding region are being tested for case association and outbreak tracking. Although measles virus is a single serotype, there are genomic differences among genotypes, including variations in B-cell and T-cell epitopes. However, current live attenuated vaccines remain sufficiently effective against all genotypes. On the other hand, the maintenance of protective immunity in vaccinees may become increasingly important, since vaccine-induced immunity tends to wane over time unlike the more durable immunity following natural infection.
H5 high pathogenicity avian influenza viruses, which emerged in Guangdong Province, China, in 1996, has now been persistently transmitted among various wild birds due to the "silent spreading" of the viruses among vaccinated poultry and domestic waterfowl. These viruses traveled long distances along with bird migration; therefore, the threat of H5 high pathogenicity avian influenza viruses is now a global issue. Furthermore, infection in wild mammals has become more prominent since 2020. The contamination of the wild bird population by the virus is considered to be an irreversible situation, and thus, the reduction of virus levels in the environment is an urgent issue to prevent further deterioration of the situation. This review will describe the history and current situations of influenza virus infection in wild birds and mammals, and discuss the research and countermeasures that are required to stop the damage caused by this virus.
The virus nomenclature working group (VNWG) was launched to officially fix Japanese names of important viruses under the Japanese Society for Virology (JSV) in 2022. VNWG first determined the priority viruses for the society and called opinions from many experts and relevant scientific societies. Its finalized list, now publicized in the JSV official web page , includes plant viruses ⁄viroids occurring⁄occurred in Japan, algal and fungal viruses associated with Japan, pathogenic human and animal viruses. In principle, a sole Japanese name was assigned to each of these viruses, and shown under the corresponding taxonomical species in the Virus Metadata Resources (VMR_MSL39_v1) issued by the International Committee on Taxonomy of Viruses (ICTV). In this article, we also touched three marked modifications in recent virus taxonomy of the ICTV: 1) adoption of a binominal system into the virus species names, 2) development of higher ranks, such as realm and kingdom, of virus taxa, and 3) approval of virus species based only upon coding-complete genomic sequences without any biological data. Also introduced in this article are what background was behind the launching of VNWG, what VNWG discussed and what issues VNWG recognized. We hope that our attempts and efforts contribute to establish the "grammar of virology": virus nomenclature and taxonomy in Japanese communication.
Biosafety Level 4 facilities have been established in our country to promote research and development and national capacity of diagnostic test systems for infectious diseases, including highly pathogenic viruses. In particular, the operation of a suit-type laboratory requiring positive pressure protective suits is a first for our country, and it is necessary to establish unique safety management technology. With the support of the Research Program on Emerging and Re-emerging Infectious Diseases of the Japan Agency for Medical Research and Development (AMED), we conducted research entitled "Study of Practical Biorisk Management in the Microbiological Containment Laboratories" from 2021 to 2023, with the aim of improving biosafety management technology in Japan. We have summarized our research project and its results obtained for the future direction of biorisk management research in Japan.
The H5N1 highly pathogenic avian influenza virus (HPAIV) of clade 2.3.4.4b emerged in Europe during 2020-2021 and rapidly spread worldwide via migratory birds, causing outbreaks in poultry, wild birds, and wildlife. Sporadic cases of human infection, likely resulting from close contact with infected animals, have been reported. In March 2024, clinical signs (e.g., reduced feed intake, altered milk quality, and decreased milk production) were observed in dairy cattle on a farm in Texas, USA, where H5N1 HPAIV was subsequently isolated. By December 2024, infections had been reported in dairy cattle across 15 states in the USA. Cases of infection have also been documented in cats near affected farms and in humans suspected of exposure through contact with infected cattle or chickens that acquired the virus from cattle. These developments have raised concerns about the potential for further transmission of H5N1 HPAIV to humans. In recent studies, H5N1 HPAIV strains isolated from cattle and humans exhibited high pathogenicity in mice and ferrets. Furthermore, ferret studies showed efficient transmission via respiratory droplets. This unprecedented spread of H5N1 HPAIV among mammals raises concerns about the emergence of a virus capable of efficient human-to-human transmission via respiratory droplets. Continued global surveillance of infection dynamics is essential to mitigate this potential public health threat.
