Questions

Classification and Nomenclature of Viruses — Questions

Study questions for Classification and Nomenclature of Viruses.

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Sit this set one question at a time. Multiple-choice questions mark themselves; written questions reveal a tickable mark scheme so you can score your own answer. You get a combined score at the end.

32 questions: 32 MCQ, 0 written.

High-priority (past-paper) questions only

The two are unrelated concepts that happen to share a word. The taxonomic class is one rung of the 15-rank hierarchy (suffix -viricetes); a Baltimore class groups viruses by the route from genome to messenger RNA.

The vernacular name denotes the agent; the binomial denotes the taxonomic species. Vernacular virus names are unregulated by the ICTV.

Baltimore sorts viruses into seven classes by the route from genome to messenger RNA. It is non-hierarchical and complements, rather than replaces, ICTV taxonomy.

Realm, kingdom, phylum and class were added, all sitting above order. The basal rank is “realm”, not “domain”.

The 15-rank, Linnaean-like hierarchy was ratified in two ICTV votes, in 2018 and 2019.

A polythetic class is defined by multiple shared characters, none individually required, which is why species rest on multiple criteria and tolerate within-species variation.

Unlike cellular life, viruses do not descend from a single common ancestor; the system reflects several separate roots, so there is no single virosphere-wide tree.

Species names are binomial: a genus name plus a single-word epithet, mirroring the Linnaean convention used across biology.

Only genus and species assignment is obligatory; higher ranks are populated only where the evidence justifies them, so most viruses are not placed at all 15 levels.

The ICTV defines a species as a monophyletic group distinguished by multiple criteria, set per family by the relevant Study Group.

“Arbovirus” requires genuine replication in the arthropod vector; passive mechanical carriage (the “flying pin”) does not qualify. Arboviruses span several families.

The measles species is Morbillivirus hominis (genus plus one-word epithet, italicised, genus capitalised). “Measles virus” is the vernacular agent name; “Measles morbillivirus” is a superseded transitional form.

Realm = -viria. (Order = -virales, family = -viridae, subfamily = -virinae, genus = -virus, phylum = -viricota, class = -viricetes.)

The three primary criteria are the genome (type, character, sequence), the replication strategy, and the virion structure. Options naming virion size or serology are the older, pre-molecular criteria.

For many virus–disease links, “risk factor” describes the relationship better than an absolute “cause”: disease appears in only a fraction of the infected, and a syndrome may have several causes.

These are informal categories defined by how a virus spreads and where it replicates; one family can appear in several, and they cut across the formal taxonomy.

Ribozyviria contains small circular RNA agents with self-cleaving ribozymes, including hepatitis delta virus.

The genus (and subgenus) suffix is -virus, as in Morbillivirus within Morbillivirus hominis.

Whole-genome sequencing is a modern criterion, not one of the historical five (nucleic-acid type, virion size, morphology, stability, antigenicity).

Riboviria gathers RNA viruses replicating via an RNA-directed polymerase together with the reverse-transcribing viruses; HIV-1 sits in Riboviria, kingdom Pararnavirae.

Sub-species labels are clinically and epidemiologically important but fall outside the ICTV’s remit; conventions vary from virus to virus.

Since 2018 every species must belong to a genus, a requirement not previously enforced. The type-species concept, by contrast, was abolished in 2021.

Hepatitis A, B, C, D and E belong to five unrelated families; the grouping is by target organ, not taxonomy.

The 2009 H1N1 virus was a reassortant carrying segments from four ancestral lineages: North American swine, North American avian, human, and Eurasian swine influenza.

A realm groups viruses by deeply shared genes and proteins, not descent from one ancestor, so it deliberately avoids the single common ancestry that “domain” implies for cellular life.

The binomial mandate was ratified in 2021 and essentially completed at the February 2025 ratification vote, so almost all species names are now binomial.

A sequence compared against reference genomes places an isolate in a taxon almost immediately, so partial sequencing is often the earliest step.

The ICTV is the single body that sets viral taxonomy and the naming of taxa. NCBI and GenBank host sequence data but do not classify viruses.

Oncogenic potential is recognised in Herpesviridae, Adenoviridae, Papillomaviridae, Polyomaviridae, Hepadnaviridae, Retroviridae and Flaviviridae, but not the Picornaviridae.

Duplodnaviria gathers double-stranded DNA viruses sharing the HK97-fold capsid (herpesviruses, tailed bacteriophages). Varidnaviria is defined instead by the jelly-roll fold.

Formal taxon names are capitalised and italicised with the rank label preceding (the genus Morbillivirus); vernacular names are lowercase, not italicised, and set informally outside ICTV control.

Fredricks and Relman (1996) recast the postulates as molecular guidelines (sequence detection, specificity, treatment response, temporality, plausibility, biological gradient, consistency). Rivers (1937) and Evans (1982) had earlier adapted the bacterial postulates to viruses.

High priorityMCQ
How does a virus's taxonomic class relate to its Baltimore class?
- A. They are synonymous
- B. They are unrelated concepts that share a word
- C. A Baltimore class is a rank within the taxonomic hierarchy
- D. The taxonomic class replaced the Baltimore system in 2018
- E. The taxonomic class sits just below the order rank
Show answer
Correct answer: B
The two are unrelated concepts that happen to share a word. The taxonomic class is one rung of the 15-rank hierarchy (suffix -viricetes); a Baltimore class groups viruses by the route from genome to messenger RNA.
High priorityMCQ
Regarding "measles virus" and *Morbillivirus hominis*, which is correct?
- A. They are interchangeable synonyms, both governed directly by the ICTV
- B. "Measles virus" is the formal species name, and the binomial is vernacular
- C. Both "measles virus" and Morbillivirus hominis are vernacular names
- D. Morbillivirus hominis is an obsolete name that is no longer used at all
- E. "Measles virus" is the vernacular agent name; Morbillivirus hominis the formal species
Show answer
Correct answer: E
The vernacular name denotes the agent; the binomial denotes the taxonomic species. Vernacular virus names are unregulated by the ICTV.
High priorityMCQ
The Baltimore classification sorts viruses on what basis?
- A. Capsid symmetry (icosahedral, helical, complex)
- B. Presence or absence of a lipid envelope
- C. Host kingdom (animal, plant, fungal, bacterial)
- D. Whether the virus is oncogenic
- E. The route from genome to messenger RNA
Show answer
Correct answer: E
Baltimore sorts viruses into seven classes by the route from genome to messenger RNA. It is non-hierarchical and complements, rather than replaces, ICTV taxonomy.
High priorityMCQ
The expanded hierarchy added four new principal ranks. Which set is correct?
- A. Domain, kingdom, phylum, class
- B. Realm, kingdom, phylum, class
- C. Realm, division, phylum, cohort
- D. Empire, realm, kingdom, phylum
- E. Realm, kingdom, tribe, class
Show answer
Correct answer: B
Realm, kingdom, phylum and class were added, all sitting above order. The basal rank is “realm”, not “domain”.
High priorityMCQ
The traditional five-rank hierarchy (species, genus, subfamily, family, order) was expanded by the ICTV into how many ranks, and over what period was the change ratified?
- A. 10 ranks, ratified 2012
- B. 12 ranks, ratified 2016–2017
- C. 15 ranks, ratified 2018–2019
- D. 15 ranks, ratified 2024–2025
- E. 8 ranks, ratified 2020
Show answer
Correct answer: C
The 15-rank, Linnaean-like hierarchy was ratified in two ICTV votes, in 2018 and 2019.
High priorityMCQ
Viral taxonomy is "polythetic". What does this mean?
- A. Every member of a taxon must share one single essential defining property
- B. A taxon rests on shared properties, none individually essential
- C. A single virus may belong to several different taxa at once
- D. Taxa are defined purely by measured phylogenetic distance
- E. Membership is settled by majority vote of the Study Group members
Show answer
Correct answer: B
A polythetic class is defined by multiple shared characters, none individually required, which is why species rest on multiple criteria and tolerate within-species variation.
High priorityMCQ
Virus taxonomy is described as "deliberately non-systematic" and polyphyletic. Which statement best explains why?
- A. They mutate too fast for any classification to remain stable
- B. They cannot be sequenced reliably, so relationships are only guessed
- C. The ICTV randomises assignments deliberately to avoid systematic bias
- D. They arose from several independent origins, so fit no single tree
- E. They are not alive, so evolutionary terms cannot apply to them
Show answer
Correct answer: D
Unlike cellular life, viruses do not descend from a single common ancestor; the system reflects several separate roots, so there is no single virosphere-wide tree.
High priorityMCQ
What format does the ICTV now mandate for **every** virus species name?
- A. A single Latinised word ending in the suffix -virus, capitalised
- B. The vernacular virus name, written entirely in capitals
- C. A polynomial describing the genome type and natural host
- D. A binomial of a genus name plus a one-word epithet
- E. A unique numeric accession code issued on registration
Show answer
Correct answer: D
Species names are binomial: a genus name plus a single-word epithet, mirroring the Linnaean convention used across biology.
High priorityMCQ
When assigning a newly discovered virus, which rank(s) must a virologist assign as a minimum?
- A. Realm and species
- B. Family and genus
- C. Genus and species
- D. All 15 ranks
- E. Species only
Show answer
Correct answer: C
Only genus and species assignment is obligatory; higher ranks are populated only where the evidence justifies them, so most viruses are not placed at all 15 levels.
High priorityMCQ
Which best states the current ICTV concept of a virus *species*?
- A. Any group of viruses that happens to infect the same host
- B. A group of viruses sharing essentially identical genome sequences
- C. A monophyletic group distinguishable from others by multiple criteria
- D. A single virus isolate maintained as a reference strain
- E. Any cluster of viruses sharing one essential defining property
Show answer
Correct answer: C
The ICTV defines a species as a monophyletic group distinguished by multiple criteria, set per family by the relevant Study Group.
High priorityMCQ
Which feature is **essential** for a virus to be classed as an arbovirus?
- A. It replicates within a blood-feeding arthropod before transmission to a vertebrate
- B. It causes a haemorrhagic fever in the infected vertebrate host
- C. It is transmitted specifically by mosquitoes and no other arthropod vectors
- D. It is carried mechanically on arthropod mouthparts between hosts
- E. It belongs to the family Flaviviridae or a closely related family
Show answer
Correct answer: A
“Arbovirus” requires genuine replication in the arthropod vector; passive mechanical carriage (the “flying pin”) does not qualify. Arboviruses span several families.
High priorityMCQ
Which is a correctly formatted **current** (binomial) virus species name?
- A. Measles virus
- B. Measles morbillivirus
- C. MEASLES VIRUS
- D. Human morbillivirus 1
- E. Morbillivirus hominis
Show answer
Correct answer: E
The measles species is Morbillivirus hominis (genus plus one-word epithet, italicised, genus capitalised). “Measles virus” is the vernacular agent name; “Measles morbillivirus” is a superseded transitional form.
High priorityMCQ
Which rank–suffix pairing is correct?
- A. Order = -viridae
- B. Family = -virales
- C. Genus = -virinae
- D. Class = -viricota
- E. Realm = -viria
Show answer
Correct answer: E
Realm = -viria. (Order = -virales, family = -viridae, subfamily = -virinae, genus = -virus, phylum = -viricota, class = -viricetes.)
High priorityMCQ
Which set lists the three *primary* modern criteria used to delineate the main viral taxa?
- A. Genome type/character/sequence, replication strategy, virion structure
- B. Virion size, virion stability, antigenicity
- C. Host range, disease caused, geographic origin
- D. Nucleic acid type, serology, electron-microscopic morphology
- E. Baltimore class, transmission route, vaccine availability
Show answer
Correct answer: A
The three primary criteria are the genome (type, character, sequence), the replication strategy, and the virion structure. Options naming virion size or serology are the older, pre-molecular criteria.
MCQ
For many virus–disease associations, modern virology favours which framing?
- A. Infection is followed by disease in every case
- B. The virus is a sufficient cause in all cases
- C. Viral causation cannot be established at all
- D. The virus is best regarded as a "risk factor"
- E. Detecting viral nucleic acid confirms causation
Show answer
Correct answer: D
For many virus–disease links, “risk factor” describes the relationship better than an absolute “cause”: disease appears in only a fraction of the infected, and a syndrome may have several causes.
MCQ
Groupings such as "enteric", "respiratory" and "blood-borne" viruses are best described as:
- A. Formal orders recognised within the ICTV taxonomic hierarchy
- B. Baltimore classes defined by the route from genome to messenger RNA
- C. Informal categories based on transmission and tropism, cutting across families
- D. Exact synonyms for particular named viral genera
- E. Realms sitting at the base of the 15-rank hierarchy
Show answer
Correct answer: C
These are informal categories defined by how a virus spreads and where it replicates; one family can appear in several, and they cut across the formal taxonomy.
MCQ
Hepatitis delta virus is classified in which realm?
- A. Ribozyviria
- B. Riboviria
- C. Duplodnaviria
- D. Adnaviria
- E. It is unassigned to any realm
Show answer
Correct answer: A
Ribozyviria contains small circular RNA agents with self-cleaving ribozymes, including hepatitis delta virus.
MCQ
In a binomial species name, the genus component ends in which suffix?
- A. -viridae
- B. -virinae
- C. -virus
- D. -virales
- E. -viria
Show answer
Correct answer: C
The genus (and subgenus) suffix is -virus, as in Morbillivirus within Morbillivirus hominis.
MCQ
In the pre-molecular era, five properties were given roughly equal weight in classification. Which of the following was **not** one of them?
- A. Type of nucleic acid (DNA or RNA)
- B. Virion size
- C. Virion morphology
- D. Complete genome nucleotide sequence
- E. Virion antigenicity
Show answer
Correct answer: D
Whole-genome sequencing is a modern criterion, not one of the historical five (nucleic-acid type, virion size, morphology, stability, antigenicity).
MCQ
Into which realm are HIV-1 and the other reverse-transcribing viruses placed?
- A. They have their own realm, Retroviria
- B. Varidnaviria
- C. Riboviria
- D. Duplodnaviria
- E. They are unassigned, being neither pure DNA nor pure RNA viruses
Show answer
Correct answer: C
Riboviria gathers RNA viruses replicating via an RNA-directed polymerase together with the reverse-transcribing viruses; HIV-1 sits in Riboviria, kingdom Pararnavirae.
MCQ
Labels such as serotype, genotype, subtype, variant and vaccine strain describe lineages **below** the species level. Who governs their naming?
- A. The ICTV, under the same rules as species
- B. The WHO exclusively
- C. GenBank, automatically on submission
- D. No one; such labels are not permitted
- E. Specialty groups, outside the ICTV's remit
Show answer
Correct answer: E
Sub-species labels are clinically and epidemiologically important but fall outside the ICTV’s remit; conventions vary from virus to virus.
MCQ
Since 2018, what structural rule applies to every virus species?
- A. It must be assigned to a genus
- B. It must have a designated type species
- C. It must be assigned to all 15 ranks
- D. It must have a sequenced reference genome
- E. It must be named after its host
Show answer
Correct answer: A
Since 2018 every species must belong to a genus, a requirement not previously enforced. The type-species concept, by contrast, was abolished in 2021.
MCQ
The "hepatitis viruses" (A, B, C, D, E) are grouped together because they share the liver as their main target. Taxonomically, how related are they?
- A. They form a single family, Hepatitisviridae
- B. They belong to five entirely unrelated families
- C. They belong to two closely related genera
- D. They are all members of Riboviria
- E. They are all reverse-transcribing viruses
Show answer
Correct answer: B
Hepatitis A, B, C, D and E belong to five unrelated families; the grouping is by target organ, not taxonomy.
MCQ
The 2009 pandemic H1N1 influenza virus illustrates which evolutionary process, and from how many ancestral lineages?
- A. Antigenic drift, from a single lineage
- B. Reassortment, from four ancestral lineages
- C. Recombination, from two lineages
- D. De novo emergence, from no known ancestor
- E. Reverse transcription, from two lineages
Show answer
Correct answer: B
The 2009 H1N1 virus was a reassortant carrying segments from four ancestral lineages: North American swine, North American avian, human, and Eurasian swine influenza.
MCQ
The basal rank is called the "realm" rather than the "domain". Why?
- A. The term "domain" was already assigned to the prions
- B. It avoids implying the single common ancestry that "domain" carries
- C. The two words are synonymous, so the choice was arbitrary
- D. Realms are defined only by shared host range
- E. "Domain" is reserved for ranks above kingdom in cellular taxonomy
Show answer
Correct answer: B
A realm groups viruses by deeply shared genes and proteins, not descent from one ancestor, so it deliberately avoids the single common ancestry that “domain” implies for cellular life.
MCQ
The binomial species-name mandate was ratified and then effectively completed when?
- A. Ratified 2012, completed 2017
- B. Ratified 2018, completed 2019
- C. Ratified 2021, completed at the February 2025 vote
- D. Ratified 2024, completed 2024
- E. Still a draft proposal, not yet in force
Show answer
Correct answer: C
The binomial mandate was ratified in 2021 and essentially completed at the February 2025 ratification vote, so almost all species names are now binomial.
MCQ
What is now frequently the *earliest* step in placing a newly encountered isolate into a taxon?
- A. Inoculation into experimental animals
- B. Genome sequencing compared against reference databases
- C. Negative-contrast electron microscopy
- D. Serological neutralisation testing
- E. Virion-stability testing across pH and temperature
Show answer
Correct answer: B
A sequence compared against reference genomes places an isolate in a taxon almost immediately, so partial sequencing is often the earliest step.
MCQ
Which body is responsible for the single universal system of virus classification and the nomenclature of virus taxa?
- A. The International Committee on Taxonomy of Viruses (ICTV)
- B. The World Health Organization (WHO)
- C. The National Center for Biotechnology Information (NCBI)
- D. The International Union of Microbiological Societies, by direct member vote
- E. Each national reference laboratory, for its own region
Show answer
Correct answer: A
The ICTV is the single body that sets viral taxonomy and the naming of taxa. NCBI and GenBank host sequence data but do not classify viruses.
MCQ
Which family is **not** generally listed among the viruses with oncogenic potential?
- A. Papillomaviridae
- B. Hepadnaviridae
- C. Herpesviridae
- D. Retroviridae
- E. Picornaviridae
Show answer
Correct answer: E
Oncogenic potential is recognised in Herpesviridae, Adenoviridae, Papillomaviridae, Polyomaviridae, Hepadnaviridae, Retroviridae and Flaviviridae, but not the Picornaviridae.
MCQ
Which realm is defined by the HK97-fold major capsid protein?
- A. Riboviria
- B. Ribozyviria
- C. Varidnaviria
- D. Duplodnaviria
- E. Adnaviria
Show answer
Correct answer: D
Duplodnaviria gathers double-stranded DNA viruses sharing the HK97-fold capsid (herpesviruses, tailed bacteriophages). Varidnaviria is defined instead by the jelly-roll fold.
MCQ
Which statement about formal versus vernacular usage is correct?
- A. Formal taxon names are lowercase, with the rank label written after the name
- B. Vernacular names are italicised and capitalised like formal taxon names
- C. Vernacular names are assigned by the ICTV Study Groups themselves
- D. Formal names are capitalised and italicised; vernacular names are lowercase and unregulated
- E. There is no practical difference between the two in usage
Show answer
Correct answer: D
Formal taxon names are capitalised and italicised with the rank label preceding (the genus Morbillivirus); vernacular names are lowercase, not italicised, and set informally outside ICTV control.
MCQ
Who reframed the Henle–Koch postulates for the sequencing era (molecular detection)?
- A. Fredricks and Relman (1996)
- B. Thomas Rivers (1937)
- C. Alfred Evans (1982)
- D. David Baltimore (1971)
- E. Robert Koch, in the original bacterial formulation
Show answer
Correct answer: A
Fredricks and Relman (1996) recast the postulates as molecular guidelines (sequence detection, specificity, treatment response, temporality, plausibility, biological gradient, consistency). Rivers (1937) and Evans (1982) had earlier adapted the bacterial postulates to viruses.