In this article we present our current knowledge about double-stranded (dsDNA) viruses infecting hyperthermophilic Crenarchaeaota, the organisms which predominate in hot terrestrial springs with temperatures over 80 °C. These viruses exhibit extraordinary diversity of morphotypes most of which have not been observed among viruses from the other two domains of life, the Bacteria and the Eukarya. Also the sequences of circular and linear genomes of crenarchaeal viruses are remarkable because the vast majority of predicted genes have no homologs in the public sequence databases.

Viruses of the Crenarchaeota generally do not cause the lysis of the host cells during release of viral progeny and they persist in infected cells in stable carrier state. In accordance with this rather unsophisticated virus-host relationship, the studies of transcription of genes in rudiviruses and fusellovirus SSV1 demonstrated a simple transcriptional pattern with minimal temporal control. The replication of viral genomes has not been studied experimentally. Nevertheless, some plausible predictions about possible replication strategies could be made based on specific features of several viral genomes.

The comparative genomics studies revealed that crenarchaeal viruses form a distinctive group, unrelated to any other viruses, with a small pool of shared genes and a unique origin, or more likely, multiple origins.