Keeping up with Virus Taxonomy: Zoonotic Viruses
Posted on November 30, 2023 by Clare Baker
In the last edition of ‘Keeping up With Virus Taxonomy’ we looked at the family Adenoviridae. They are popular virus vectors and were used in vaccinations against the coronavirus SARS-CoV-2. So, let’s keep a focus on SARS-CoV-2 and start with the family Coronaviridae.
Coronaviridae
Coronaviridae, are a family of viruses in the order Nidovirales. The family are enveloped positive-sense RNA viruses that are known to infect four classes of vertebrates: mammals and birds, amphibians and bony fish. Members of the Coronaviridae family infect humans and a variety of animals, which results in diverse clinical manifestations, ranging from asymptomatic to severe fatal disease.
Of particular interest is the subfamily Orthocoronavirinae. Members of this subfamily include SARS-CoV-2, responsible for the COVID-19 pandemic, SARS-CoV, which is responsible for the SARS epidemic in 2002-2003 and MERS-CoV, responsible for the MERS epidemic starting 2012.
It is thought that the original host of both SARS-CoV and MERS-CoV were bats and then later transmitted to humans. Let’s take a look at some other virus families that contain zoonotic viruses: viruses that have jumped from a non-human to humans.
Poxviridae
Poxviridae are a family of generally oval or brick shaped viruses. Most viruses which infect humans in the Poxviridae family are zoonotic except for molluscum contagiosum virus (MCV) and the variola virus (VARV), the causative agent of smallpox, which has now been eradicated. The family includes two subfamilies, Chordopoxvirinae and Entomopoxvirinae. Members of Chordopoxvirinae include important pathogens of humans, livestock animals and wildlife. Infections typically result in the formation of lesions, skin nodules, or disseminated rash and can be fatal in some cases.
Phenuiviridae
Next up we have the family Phenuiviridae, an ecologically diverse family which infects livestock animals and humans, birds, crustaceans, plants and fungi. Different phenuivirids are transmitted by sand flies, ticks, mosquitoes, plant hoppers or other arthropod vectors and some members of the family have a very narrow host range. A typical member of the family is the Rift Valley fever virus, a viral zoonosis that mostly infects animals but also has the ability to infect humans according to the World Health Organisation.
Hepeviridae
And finally, we have Hepeviridae, which includes enterically-transmitted (through the faecal oral route) small viruses. One example of a virus belonging to the family Hepeviridae is Hepatitis E virus (HEV), the only zoonotic hepatitis virus. Chronic hepatitis E has become a concern in individuals who are immunosuppressed, especially those who have received organ transplants. There is hope, however, as vaccines capable of protecting against human infection with HEV have been produced by using portions of the capsid protein (Purdy et al., 1993, Tsarev et al., 1997).
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.
