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In the 2002 metagenomics study the researchers found that 65% of the sequences of DNA and RNA viruses had no matches in the reference databases. [10] This phenomenon of unmatched viral sequences in sequence reference databases is prevalent in viral metagenomics studies and is referred to as “viral dark matter".
All known RNA viruses, that is viruses that use a homologous RNA-dependent polymerase for replication, are categorized by the International Committee on Taxonomy of Viruses (ICTV) into the realm Riboviria. [3] This includes RNA viruses belonging to Group III, Group IV or Group V of the Baltimore classification system as well as Group VI.
RNA–RNA recombination between different strains of the murine coronavirus was found to occur at a high frequency both in tissue culture [47] and in the mouse central nervous system. [36] These findings suggest that RNA–RNA recombination may play a significant role in the natural evolution and neuropathogenesis of coronaviruses. [36]
The Kermack–McKendrick epidemic model (1927) and the Reed–Frost epidemic model (1928) both describe the relationship between susceptible, infected and immune individuals in a population. The Kermack–McKendrick epidemic model was successful in predicting the behavior of outbreaks very similar to that observed in many recorded epidemics. [7]
Double-stranded RNA viruses (dsRNA viruses) are a polyphyletic group of viruses that have double-stranded genomes made of ribonucleic acid.The double-stranded genome is used as a template by the viral RNA-dependent RNA polymerase (RdRp) to transcribe a positive-strand RNA functioning as messenger RNA (mRNA) for the host cell's ribosomes, which translate it into viral proteins.
RNA viruses lack the capacity to identify and repair mismatched or damaged nucleotides, and thus, RNA genomes are prone to mutations introduced by mechanisms intrinsic and extrinsic to viral replication. [18] RNA viruses present a therapeutic double-edged sword: RNA viruses can withstand the challenge of antiviral drugs, cause epidemics, and ...
Positive-strand RNA virus genomes usually contain relatively few genes, usually between three and ten, including an RNA-dependent RNA polymerase. [4] Coronaviruses have the largest known RNA genomes, between 27 and 32 kilobases in length, and likely possess replication proofreading mechanisms in the form of an exoribonuclease within nonstructural protein nsp14.
Negative-strand RNA viruses (−ssRNA viruses) are a group of related viruses that have negative-sense, single-stranded genomes made of ribonucleic acid (RNA). They have genomes that act as complementary strands from which messenger RNA (mRNA) is synthesized by the viral enzyme RNA-dependent RNA polymerase (RdRp). During replication of the ...