Classification of Viruses
The classification of viruses involves organizing them into groups based on their genetic material, structure, replication process, and other characteristics. Viruses are classified into families, genera, and species, with the International Committee on Taxonomy of Viruses (ICTV) overseeing the naming and classification process. This system helps scientists understand the diversity and relationships among different viruses.
7 Key excerpts on "Classification of Viruses"
eBook - ePub- Britannica Educational Publishing, Kara Rogers(Authors)
- 2010(Publication Date)
- Britannica Educational Publishing(Publisher)
...The icosahedral viruses are further subdivided into families based on the number of capsomeres making up the capsids. Finally, all viruses fall into two classes depending on whether the nucleocapsid is surrounded by a lipoprotein envelope. Some virologists adhere to a division of viruses into those that infect bacteria, plants, or animals; these classifications have some validity, particularly for the unique bacterial viruses with tails, but there is otherwise so much overlap that taxonomy based on hosts seems unworkable. Classification based on diseases caused by viruses also is not tenable, because closely related viruses frequently do not cause the same disease. Eventually, it is likely that the Classification of Viruses will be based on their nucleotide sequences and their mode of replication, rather than on structural components, as is now the case. The basic taxonomic group is called a family, designated by the suffix -viridae. The major taxonomic disagreement among virologists is whether to segregate viruses within a family into a specific genus and further subdivide them into species names. In the first decade of the 21st century, there occurred a shift toward the use of binomial nomenclature—as used for bacteria—dividing viruses into italicized genera and species. This move was prompted in large part by the International Committee on Taxonomy of Viruses (ICTV), a member group of the International Union of Microbiological Societies. The ICTV oversees the ongoing process of devising and maintaining a universal classification scheme for viruses. In the virus classification hierarchy, the ICTV recognizes orders, families, subfamilies, genera, and species. The placement of viruses in these groups is based on information provided by study groups comprised of experts on specific types of viruses. In the ICTV system, each species of virus is generally recognized as representing a group of isolates, or viruses with distinct nucleic acid sequences...
eBook - ePub- Volodymyr Ivanov(Author)
- 2020(Publication Date)
- CRC Press(Publisher)
...10 Classifications of Viruses and Microorganisms Biological Classification Biological classification is the conventional grouping of biological objects. This classification of biological objects can be based on phenotype, i.e. on observable morphological, physiological, biochemical, and ecological characteristics, as well as on genotype, i.e. on inherited traits that are coded in the sequence of DNA. The classifications are used for understanding the mechanisms of diversity of the studied groups and for the identification of new biological objects. Units of Biological Classification The elementary unit of microbiological classification is a microbial strain (microorganisms isolated from one colony) or a clone (microorganisms originated from one organism). Similar strains with similar phenotypes and genotypes are combined conventionally in a species (pl. specia). Higher classification units are genus (pl. genera), family, order, and kingdom. Name of the Species The names of species are conventionally given and read in Latin and include the names of both genus and species : for example, Bacillus subtilis (meaning a species subtilis inside the genus Bacillus), Escherichia coli (a species coli inside the genus Escherichia), or Pseudomonas aeruginosa (a species aeruginosa inside genus Pseudomonas). After the first mention of a full name in a scientific report, for example the species Bacillus subtilis, a researcher may then write B. subtilis. The name Bacillus sp. in the scientific report means that the species from the genus Bacillus was not defined. The name Bacillus spp. means the numerous species from the genus Bacillus. The names Bacillus Subtilis, Bacillus Subtilis, or bacillus subtilis, if given in a research report, would mean that the researcher did not study and does not know microbiology at all. Classification of Viruses Viruses are particles that are self-assembled from biopolymers and are capable of multiplying inside living prokaryotic or eukaryotic cells...
eBook - ePub- Jane Flint, Vincent R. Racaniello, Glenn F. Rall, Theodora Hatziioannou, Anna Marie Skalka(Authors)
- 2020(Publication Date)
- ASM Press(Publisher)
...Although a subsequently formed international committee on the nomenclature of viruses did not adopt this system in toto, its designation of orders, families, genera, and species is used for the classification of animal viruses. One of the most important principles embodied in the system advanced by Lwoff and his colleagues was that viruses should be grouped according to their shared properties rather than those of the cells or organisms they infect. A second principle was a focus on the nature of the nucleic acid genome as the primary criterion for classification. The importance of the genome had become clear when it was inferred from the Hershey-Chase experiment that viral nucleic acid alone can be infectious (Box 1.5). Four characteristics are used in the taxonomic classification of all viruses: BOX 1.9 TERMINOLOGY Complexities of viral nomenclature No consistent system for naming viral isolates has been established by their discoverers. For example, among the vertebrate viruses, some are named for the associated diseases (e.g., poliovirus, rabies virus), for the specific type of disease they cause (e.g., murine leukemia virus), or for the sites in the body that are affected or from which they were first isolated (e.g., rhinovirus and adenovirus). Others are named for the geographic locations from which they were first isolated (e.g., Sendai virus [Sendai, Japan] and Coxsackievirus [Coxsackie, NY]) or for the scientists who first discovered them (e.g., Epstein-Barr virus). In these cases, the virus names are capitalized. Some viruses are even named for the way in which people imagined they were contracted (e.g., influenza, for the “influence” of bad air), how they were first perceived (e.g., the giant mimiviruses [ Box 1.10 ], for the fact that they “mimic” bacteria), or totally by whimsy (e.g., Pandoravirus, after Pandora’s jar [later box] of Greek mythology)...
eBook - ePub- Michel Tibayrenc(Author)
- 2017(Publication Date)
- Elsevier(Publisher)
...1 Recent Developments in the Definition and Official Names of Virus Species ∗ M.H.V. Van Regenmortel Université de Strasbourg-CNRS, Illkirch Cedex, France Abstract Classification deals with abstract classes and taxonomy deals with classes called taxa. Viral taxonomy refers both to the scientific discipline of virus classification and to the outcome of a classification activity involving viruses. Keywords Virus species; ICTV; Monothetic; Polythetic; Viral genomes; Viral taxonomy; Virus classification 1. Introduction Classification deals with abstract classes and taxonomy deals with classes called taxa. Viral taxonomy refers both to the scientific discipline of virus classification and to the outcome of a classification activity involving viruses. Virus classification deals with abstract classes of viruses that are conceptual constructions of the mind. The most important characteristic of such classes is that they have members that are the concrete viral objects studied by virologists. Every membership condition determines a class and if a virus has a monopartite negative strand RNA genome, it automatically becomes a member of the Mononegavirales, which is a class known as an order. 1 Such a class is not physically real and must not be confused with the viruses themselves. Similarly, the abstract concept of a virus species as a class of viruses should not be confused with the viruses that are the concrete members of the species. Confusions between different logical categories have been a fertile source of misunderstandings in viral taxonomy...
eBook - ePubTaxonomic Guide to Infectious Diseases
Understanding the Biologic Classes of Pathogenic Organisms
- Jules J. Berman(Author)
- 2019(Publication Date)
- Academic Press(Publisher)
...Furthermore, within a class of cellular organisms, there are only rare instances of classes of virus that can infect distantly related subclasses. For example, there are virtually no viruses that can infect both Class Animalia and Class Plantae (rare exceptions are claimed [40]). Furthermore, as the host evolves, so must the virus. Hence, we might expect to find ancestral lineages of viruses that shadow the lineage of their host organisms. The relatively recent discovery of NCLDVs (nucleocytoplasmic large DNA viruses, popularly known as giant viruses) has greatly expanded our notion of viral existence [45, 46]. The life of an NCLDV is not much different from that of obligate intracellular bacteria (e.g., Rickettsia). The NCLDVs, with their large genomes and complex sets of genes, have provided taxonomists with an opportunity to establish ancestral lineages among some of these viruses [45, 46]. At this time, the Classification of Viruses is somewhat crude. Anything you choose as a classifying principle fails to biologically unify the subclasses. For example, if you classify viruses by their genomic molecules (i.e., DNA or RNA, single strandedness or double strandedness), you will find that subclasses with the same genomic type will have dissimilar structures: envelope, size, shape, proteins, and capsid. When we list viruses based on method of contagion, by persistence within host (i.e., acute, chronic, latent, or persistent), toxicity (lytic, immunogenic), or by target cell specificity, no consistent taxonomic correlation is found. Though we cannot as yet classify viruses strictly by their evolutionary lineage, we can usefully group viruses based on the physical characteristics of their genomes. The Baltimore Classification divides viruses into seven groups based on whether their genome is DNA, RNA, single stranded, or double stranded, the sense of the single strand, and the presence or absence of a reverse transcriptase. Here are the classes of the pathogenic viruses...
eBook - ePub- Richard L. Hodinka, Stephen A. Young, Benjamin A. Pinksy, Richard L. Hodinka, Stephen A. Young, Benjamin A. Pinksy(Authors)
- 2016(Publication Date)
- ASM Press(Publisher)
...Prevention of cervical cancer and other cancers is now feasible because of the availability of HPV vaccines. VIRAL CLASSIFICATION AND BIOLOGY Papillomaviruses are small, circular, nonenveloped double-stranded DNA viruses (∼55 nm in diameter) and taxonomically belong to the family Papillomaviridae (1). These viruses infect a number of hosts including various animals from birds to mammals and can cause benign wartlike lesions or produce malignant disease in the form of cervical or other cancers. The family Papillomaviridae contains approximately over 200 papillomavirus types, in five genera, infecting over 49 species, human, mammalian, reptilian and avian (2, 3). The five major genera include α-papillomavirus, β-papillomavirus, γ-papillomavirus, mu-papillomavirus, and nu-papillomavirus; classification is based on the nucleotide sequence of the open reading frame(ORF) coding for the L1 capsid protein (2). Classification of HPV into different genera is predicated on less than 60% nucleotide sequence similarity within the L1 portion of the genome for each HPV genus. Within a genus, different viral species typically share between 60 to 70% homology of the viral genome. For an HPV type to be novel, that virus must have less than 90% nucleotide similarity to any other HPV type known at the time of discovery (2). Nomenclature designation for papillomaviruses is determined by the papillomavirus study group, which is part of the International Committee on Taxonomy of Viruses (ICTV). It is estimated that almost 400 HPV types actually exist. HPV classification is managed by the International HPV Reference Center in Stockholm, Sweden. When the center receives new and novel HPV types, they are recloned and resequenced and if confirmed to be a new HPV type, assigned a type designation. All reference clones are listed on the following web site, www.hpvcenter.se, which is available for public access (2)...
eBook - ePubPrinciples of Virology, Volume 1
Molecular Biology
- Jane Flint, Vincent R. Racaniello, Glenn F. Rall, Theodora Hatziioannou, Anna Marie Skalka(Authors)
- 2020(Publication Date)
- ASM Press(Publisher)
...For those who prefer to teach virology based on specific viruses or groups of viruses, the material in this chapter can be used to structure individual reading or to design a virology course while adhering to the overall organization of this textbook by function. Reference to this chapter provides answers to questions about specific virus families. For example, Fig. 3.5 provides information about (+) strand RNA viruses and Fig. 3.10 indicates specific chapters in which these viruses are discussed. Since the earliest days of experimental virology, genetic analysis has been essential for studying viral genomes. Initially, methods were developed to produce viral mutants by chemical or UV mutagenesis, followed by screening for readily identifiable phenotypes. Because it was not possible to identify the genetic changes in such mutants, it was difficult to associate proteins with virus-specific processes. This limitation was surmounted with the development of cloned infectious DNA copies of viral genomes, an achievement that enabled the introduction of defined mutations. These methods for reducing or ablating the expression of specific viral or cellular genes comprise a complete genetic toolbox that provides countless possibilities for studying the viral genome and the interaction of viral gene products with those of the cell. The ability to manipulate cloned DNA copies of viral genomes has also enabled the development of viruses as vectors for the expression of foreign genes, for gene therapy, viral oncotherapy, and to deliver vaccines to prevent infectious diseases. How ironic it is that our study of the viruses that cause disease has led to their transformation into therapeutic agents! REFERENCES Review Articles Baltimore D. 1971. Expression of animal virus genomes. Bacteriol Rev 35: 235–241. Knott GJ, Doudna JA. 2018. CRISPR-Cas guides the future of genetic engineering. Science 361: 866–869. Krupovic M, Dolja VV, Koonin EV. 2019...
