Discovery of New Giant Virus 'Furtivovirus' in Freshwater of Kamakura, Kanagawa Prefecture: Proposal for a New Family and Higher-Order Classification Order

【Research Summary and Key Points】
Researchers have discovered a new giant virus, 'Furtivovirus,' in the Inase River in Kamakura, Kanagawa Prefecture.
It was revealed that Furtivovirus has a unique replication strategy of forming viral particles within the nucleoplasm while destroying the host cell's nuclear membrane.
Comparative genomic analysis indicated that four species, including Furtivovirus, form a new family named 'Manesviridae,' which is a sister group to the known giant virus family, Mimiviridae (Mamomovirus family). The researchers proposed the creation of a new 'order' that integrates both groups.

【Research Overview】
Led by Jiwan Bae (first-year doctoral student at the Graduate School of Science, Tokyo University of Science) and Professor Masaharu Takemura (Department of Science Communication, Faculty of Science Division I), the research team discovered Furtivovirus in freshwater in Kamakura.

Genomic analysis revealed that this virus is closely related to Clandestinovirus, a giant virus previously discovered in France. Comparative genomic analysis further showed that the four species, including Furtivovirus, constitute the new family 'Manesviridae,' which sits as a sister group to the Mamomovirus family. Consequently, the team proposed the creation of a new 'order' (name yet to be set) to integrate both, rather than placing them in the Pandoravirales order as previously thought.

Furthermore, electron microscopy revealed that Furtivovirus has a unique replication strategy: destroying the host nuclear membrane and forming viral particles inside the nucleus. This strategy differs from that of previously discovered giant viruses like Medusavirus or Ushikuvirus. Comparing these viruses, which utilize host cell nuclei differently during replication, is expected to help decipher the evolutionary pathways of the interaction between viruses and host cell nuclei.

This discovery provides further evidence for the 'Viral Eukaryogenesis Hypothesis' proposed by Professor Takemura and is expected to contribute to the understanding of the origin and evolution of eukaryotes, including humans.

These research results were published online in the international academic journal 'Journal of Virology,' issued by the American Society for Microbiology, on May 14, 2026.