Which virus has the largest physical particle diameter?

The biggest virus ever found is Megaklothovirus horridgei, which can grow up to 3,900 nanometers (nm) long. It was discovered on an arrow worm in 2018, breaking the record previously held by the Pithoviruses.

Other giant viruses include:

• Pithovirus sibericum: Once considered the largest, this virus is shaped like a prolate spheroid and measures up to 2,500 nm long and 900 nm wide. It was revived from 30,000-year-old Siberian permafrost.
• Tupanvirus: Found in Brazil in both a soda lake and ocean sediments, this virus has an icosahedral capsid with a long tail, reaching up to 2,300 nm in length.
• Pandoravirus salinus: Discovered in 2013, this virus measures about 1,000 nm long and 500 nm wide. Interestingly, it carries a genome larger than many bacteria.
• Mimivirus: First described in 2003, this giant virus has a capsid diameter of 500 nm. Including its outer fiber layer, it reaches an overall diameter of about 750 nm.