Keeping up With Virus Taxonomy: dsDNA genomes

Posted on September 15, 2023   by Clare Baker

Welcome back to Keeping up with Virus Taxonomy. The ICTV Virus Taxonomy Profiles of Simuloviridae and Poxviridae were both published in the Journal of General Virology this year, but that’s not the only thing they have in common: their genomes are both in the form of double stranded deoxyribonucleic acid or dsDNA. Let’s take a look at them and some other viruses whose genomes are in this structure for this edition of ‘Keeping up With Virus Taxonomy’.

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Let’s start with the newly published Poxviridae. Members of this virus family are enveloped and generally oval or brick shaped. Their genome is a linear module of dsDNA with covalently closed ends. Poxviridae include important pathogens of humans, livestock, animals and wildlife. You may be familiar with a member of this virus family, - variola virus, which is the causative agent of smallpox. Transmission of Chordopoxvirinae, a sub family of Poxviridae, occurs by droplet/aerosol; direct contact; arthropods (via mechanical means) or indirect contact via fomites (inanimate objects).  


Next we have Adenoviridae. This family of viruses also have a linear dsDNA genome. They infect a variety of vertebrate hosts, from fish to humans. The variety of this virus family doesn’t stop there, the severity of infections also varied from subclinical to lethal. You may have come across the Adenovirus family before as they are popular virus vectors used in vaccination. Adenoviridae were used in initial vaccines against the coronavirus SARS-CoV-2. 


Our next virus family, Herpesviridae, has a brand-new name: Orthoherpesviridae. Members of this family have linear, dsDNA genomes of 125-241 kilo base pairs and contain 70-71 genes. 43 of these genes have been inherited from a single ancestral herpesvirus. As the name gives away, the sexually transmitted infection, herpes simplex virus, belongs to this family. Members of the Orthoherpesviridae family are highly adapted to their hosts and have closely co-evolved with them. They also establish life-long latent infections with their host, during which there is limited viral gene expression and transmission of infection. In some instances, this close evolution has led to the downfall of some species within the family as they became extinct with their host. The Orthoherpesviridae family persists, however, as there is evidence of instances of cross-species transmission. 


And finally, the last virus family with a dsDNA genome on our list is Simuloviridae. Unlike any of the other families in the ‘Keeping up With Virus Taxonomy’ line up, members of the Simuloviridae family have a dsDNA held in a circular formation. These viruses infect halophilic (thrives in high salt conditions) archaea in the class Halobacteria. They are temperate viruses, meaning that the infection from a member of the family does not immediately result in cell death, instead, their virus genome resides in the host cell. This may be why members of the family were initially identified as plasmids in their host cells and were only later identified as legitimate viruses. This is also where the family gets its name, from the Latin ‘simulo’, meaning pretend.  

The International Committee on Taxonomy of Viruses (ICTV) is responsible for developing and maintaining a universal virus taxonomy. Known viruses are categorised into a classification scheme taking into consideration their physical and biological properties in combination with their phylogenetic relationships.

These two-page summaries of each chapter of the ICTV Report (a free resource published by the ICTV which provides an up-to-date description of virus taxonomy) are freely available in the Journal of General Virology, and are supported by the Microbiology Society. These summaries are known as ICTV Virus Taxonomy Profiles and describe the structure, replication and taxonomy of each virus order and family.