Virus

A virus is a nucleotide sequence that can only replicate within a host organism. Viruses can infect animals, plants, and bacteria.

• International Committee on Taxonomy of Viruses

A virus is made up or a core of genetic material, which can be either DNA or RNA, that is surrounded by a capsid that gives it physical structure and protection in many environments.

• Adenovirus
• Coronavirus

Since viruses do not replicate without hosts, there has long been debate about whether or not viruses are alive or should be considered their own kingdom of life.

Because viruses are extremely small and even a small ecology of them may contain a spectrum of genetic variance, some scientists have begun to examine viruses at the group level of constitution.¹⁾

• Dec 2011 - Quasispecies as a matter of fact: Viruses and beyond
  • Mutant spectra act as interacting sets of variant viruses subjected to group selection.
  • The target of selection may be realized through complementing or interfering interactions.
  • Cooperative interactions can modulate virulence in bacteria.
  • Cellular heterogeneity lies at the basis of tumor progression.
  • Prions become heterogeneous by accumulating protein-folding mutants.

Viruses are challenging to isolate since they require cells for replication.²⁾ Viruses including rhinovirus and bovine diarrhea virus have been isolated, sometimes using intermediate tissue cultures.³⁾

Most scientists believe that a small portion of viruses are pathogenic to their hosts.

• Testing for Viruses in Humans

https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC6797082/

https://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1008271