[Giant viruses: update, enigmas, controversies and perspectives]

Area of Science:

• Virology
• Microbiology

Background:

• Historically, viruses were defined by their small size, unable to pass through porcelain filters.
• This filtration property was a key criterion for identifying viruses for over a century.

Observation:

• The discovery of Mimivirus in 2003 revealed exceptions to the size-based definition.
• Mimivirus was initially misclassified as a bacterium due to its large size.

Findings:

• Non-filtering "giant viruses" are now recognized as common and diverse.
• These viruses vary significantly in virion shape, genome size, gene content, and replication.

Implications:

• The existence of giant viruses necessitates a re-evaluation of viral classification and definition.
• This rapidly expanding field of virology presents new enigmas and research perspectives.