From the same Siberian permafrost where three others were previously discovered, scientists find a fourth type of giant virus.

Mollivirus sibericum is the newest member of a family of ancient giant viruses isolated from a sample of Siberian permafrost, researchers from France’s CNRS L’Institut de Microbiologie de la Méditerranée and their colleagues reported in PNAS this month (September 2). M. sibericum, estimated to be around 30,000 years old, joins Mimivirus, Pandoraviruses, and Pithovirus sibericum. All four giant viruses have been found to infect amoebas.

Scanning electron microscopy of particles of four families of giant viruses. The largest dimensions can reach between 0.6 microns (Mollivirus) and 1.5 microns (Pandoravirus).

That the newly discovered virus can infect an amoeba points to its pathogenic potential, study coauthor Jean-Michel Claverie told the Agence France-Presse. “A few viral particles that are still infectious may be enough, in the presence of a vulnerable host, to revive potentially pathogenic viruses,” said Claverie.