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

Viral Structure

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.

Types of Viruses

Theories of Viruses

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.

Quasispecies Swarms

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.

Challenges in Studying Viruses

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)

Pathogenic Viruses

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

Medical Testing

December, 2011 | Samuel Ojosnegros et al | Virus Research (journal) | Quasispecies as a matter of fact: Viruses and beyond | doi: 10.1016/j.virusres.2011.09.018
November 11, 2020 | Rachael Krishna | The Covid-19 virus has been isolated many times