Virus classification

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Virus classification

There is no evidence that viruses possess a common ancestor or are in any way phylogenetically related. Nevertheless, classification along the lines of the Linnean system into families, genera, and species has been utilized. Based on the organisms they infect, the first broad division of viruses is into bacterial, plant, and animal viruses. Within these classes, other criteria for subdivision are used. Among these are general morphology; envelope or the lack of it; nature of the genome (DNA or RNA); structure of the genome (single- or double-stranded, linear or circular, fragmented or nonfragmented); mechanisms of gene expression and virus replication (positive- or negative-strand RNA); serological relationship; host and tissue susceptibility; pathology (symptoms, type of disease).

Animal viruses

The families of animal viruses are sometimes subdivided into subfamilies; the suffix -virinae may then be used. The subgroups of a family or subfamily are equivalent to the genera of the Linnean classification. See Animal virus

The animal DNA viruses are divided into five families: Poxviridae, Herpesviridae, Adeno­viridae, Papovaviridae, and Parvoviridae. RNA animal viruses may be either single-stranded or double-stranded. The single-stranded are further subdivided into positive-strand and negative-strand RNA viruses, depending on whether the RNA contains the messenger RNA (mRNA) nucleotide sequence or its complement, respectively. Further, the RNA genes may be located on one or several RNA molecules (nonfragmented or fragmented genomes, respectively). The positive-strand RNA animal viruses contain six families: Picornaviridae, Calciviridae, Coronaviridae, Togaviridae, Retroviridae, and Nodamuraviridae. The nucleocapsid of negative-strand RNA animal viruses contains an RNA-dependent RNA polymerase required for the transcription of the negative strand into the positive mRNAs. Virion RNA is neither capped nor polyadenylated. The group is divided into five families: Arenaviridae, Orthomyxoviridae, Paramyxoviridae, Rhabdoviridae, and Bunyaviridae. The double-stranded RNA animal viruses contain only one group, the Reoviridae.

Bacterial viruses

Bacterial viruses are also known as bacteriophages or phages. They may be tailed or nontailed. Nontailed phages are further subdivided into those with envelopes and those without. Tailed phages, which do not have envelopes, are divided into three families: Myoviridae, Styloviridae, and Pedoviridae. The group of nontailed DNA bacteriophages contains seven families, each with a distinctive morphology: Tectiviridae, Corticoviridae, Inoviridae, Microviridae, Leviviridae, Plasmaviridae, and Cystoviridae. Only the latter two families have envelopes. See Bacteriophage

Plant viruses

Plant viruses are divided into groups, rather than families, except those which belong to families of rhabdo viridae and reoviridae. The group, and correspondingly subgroup and type, can be viewed as analogous to family, genus, and species, respectively. Most common among plant viruses are those with a single-stranded, capped but not polyadenylated, positive-strand RNA. See Plant viruses and viroids

References in periodicals archive ?
CMX001 is a novel, broad-spectrum, oral antiviral that inhibits dsDNA viruses, including CMV, AdV, BK virus and herpes simplex virus.
As a result, this method is likely to be of greater value for organisms with dsDNA genomes such as bacteria, eukaryotic parasites, and dsDNA viruses (in which quasi-species are less common because of more accurate replication) than for organisms with single negative-stranded RNA genomes (in which quasispecies are more common because their replication depends on the error-prone reverse transcriptase--HIV, hepatitis C, hepatitis B) (39,40).
It has also been administered to more than 120 patients under investigator-held Emergency Investigational New Drug applications (EINDs) for the treatment of a wide range of life-threatening infections caused by dsDNA viruses for which there are either no approved treatments or where patients have failed the available treatment.
The company's lead candidate, CMX001, is a Lipid-Antiviral-Conjugate that delivers high intracellular levels of the active antiviral agent cidofovir-diphosphate and has broad spectrum activity against dsDNA viruses in vitro.
Through EINDs, CMX001 has been used for the treatment of a wide range of life-threatening infections caused by dsDNA viruses, including CMV, adenovirus (AdV), BK virus (BKV), Epstein Barr virus (EBV), herpes simplex virus (HSV), and JC virus (JCV), for which there are no FDA-approved treatments or where patients have failed available treatments.
The growing body of evidence of CMX001's antiviral activity against all five families of dsDNA viruses that cause morbidity and mortality in humans, including smallpox, has strengthened the compound's potential as a dual-use product prescribed as a traditional pharmaceutical and stockpiled as a biodefense countermeasure.
CMX001 is in Phase 2 clinical studies in immunocompromised transplant and cancer patients for the treatment and/or prophylaxis of dsDNA viruses, including cytomegalovirus and adenovirus.
CMX001 is in Phase 2 clinical studies in immunocompromised transplant and cancer patients for the prophylaxis and/or pre-emption of dsDNA viruses, including BK virus and adenovirus.
CMX001 is in Phase 2 clinical studies in immunocompromised transplant and cancer patients for the prophylaxis and/or pre-emption of dsDNA viruses such as cytomegalovirus and adenovirus, as well as an Open-Label Study for the treatment of patients with any of 12 different dsDNA infections that is designed to provide supportive data for CMX001's pivotal studies.
As part of progressing the clinical and non-clinical development of CMX001 for the smallpox indication, the BARDA contract will also support expanded human safety trials and the recently initiated CMX001-350 multicenter, open-label clinical study of CMX001 for the treatment of twelve life-threatening or serious conditions caused by dsDNA viruses.
The primary objective of the multicenter open-label study of CMX001 is to provide CMX001 to patients with immediately life-threatening or serious disease caused by any of 12 different viral infections resulting from dsDNA viruses.