Lecture 4 - Viral Nomenclature and Classification Flashcards
How are viruses classified?
- Viruses are classified on the basis of:
molecular architecture
genetic relatedness
host organism
More than 30,000 different virus isolates are known today
3,600 species
164 genera
71 families
Classification based on genome material and host range
What is the Baltimore classifcation of Viruses?
Classification based on genome present in virions
What is the purpose of having major viruse groups?
Study of the major groups of viruses leads to understanding of shared characteristics and replication pathways
Viruses with single-stranded DNA genomes are small and have few genes
What is positive and negative-sense ssRNA?
- *Positive-sense (+**) viral RNA is similar to mRNA and thus can be immediately translated by the host cell
- *Negative-sense (-**) viral RNA is complementary to mRNA and must be converted to positive-sense RNA before translation
What is the International Committee on Taxonomy of Viruses (ICTV)?
The Scientific name of viruses?
The list.
Formed in 1996 to develop a universal taxonomic scheme for viruses
Order (-virales)
Family (-viridae)
Subfamily (virinae)
Genus (virus)
Common name
Example: Vaccinia (common name)
Poxviridae (Family)
Chordopoxvirinae (Subfamily)
Orthopoxvirus (Genus)
6 Orders
87 Families
19 Subfamilies
348 Genera
5450 viruses belonging to >2285 virus species
Also includes viroids and prions
What is the Virus Taxonomic Key and how is it characterized/organized?
- Taxonomic key created based on molecular characteristics and measurements
- Size, shape, envelope, capsid symmetry/structure
- Physical and chemical properties
Virion molecular weight
Stability (pH, temp, , detergent, etc.)
- Genome properties
Type of nucleic acid
Complete/partial sequence
GC content, +/-5’ cap, +/- 3’ poly A tail
- Protein characteristics
Structural and non-structural
Number and sizes
Functional activities
Amino acid sequence
Posttranslational modification
- Lipids and carbohydrates too
- Life cycle
Replication strategy
Site of accumulation of virion proteins
Site of virion assembly
Nature of virion maturation and release
Biological properties
Host range
Tissue tropisms
Mode of transmission
Geographic distribution
What are some of the terms that are involved in Lower Taxonomical Hierarchies?
- *Species:** class of viruses that share several properties
- *Serotype/serovar:** variations within a viral subspecies
- *Strain:** genetic variants of the same virus; isolated from different geographic locations
- *Variant**: virus whose phenotype differs from original wild-type strain but genetic basis is unknown
What are Viral Disease Syndromes?
Syndromes: sets of symptoms and physical signs occurring together
Some viral families cause a wide variety of symptoms despite similarities in structure, size, and genomes
Lab diagnosis is critical!
What are some other major viruse groups?
Satellite viruses and satellite nucleic acids require a helper virus to replicate
Viroids do not code for proteins, but replicate independently of other viruses
Prions are “infectious” protein molecules; no nucleic acid/genomic material
What is a Giruse?
- Large ~400-800 nm in size
- Not filterable through 0.2 to 0.3 mm pores
- DNA viruses with genome >300 kb
- Infect bacteria and protists (e.g. ameoba)
- Phagocytic organisms
- Associated with aquatic environments
- Isolated from a cooling tower
- Initially thought to be Gram-positive bacteria
- Encased in polysaccahride layer
Mimivirus- “microbe mimicking virus”
1.2 megabase pair genome
Encode up to 979 proteins
Has genes coding for nucleotide and amino acid synthesis
DNA polymerase
Transcription factors (TFs)
No genes for ribosomal proteins
Lives within the amoeba host Acanthamoeba polyphaga
Bigger “Mamavirus” discovered in 2003
What is a virophage?
Virus that grows inside of a virus!
Found to multiply inside of amoeba, but only if that amoeba is infected with Mamavirus
Satellite virus: depend on co-infection of the host cell by “helper viruses”
Harnesses the Mimivirus proteins to rapidly produce new copies of itself
Growth is deleterious to Mimivirus
production of abortive forms
abnormal capsid assembly of the host virus
