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A virus is an extremely small[note 1] infectious agent. A virus consists of a protein coating over a strand of RNA or DNA, which replicates itself by taking over a host cell of another life form, implanting its genetic information into it, and causing the cell to produce more viruses.[1] In the type of reproduction used by virulent viruses, the lytic cycle,Wikipedia the host cell bursts, dispersing the new viruses. Other viruses do not destroy the host cell, but multiply by budding. With these methods of reproduction, viruses play a part in maintaining genetic diversity through transfer of genetic material between cells.[2]

Viruses cause many infectious diseases, from things as non-threatening as the Common Cold, to being Bio-Safety Level 4 pathogens, such as the Ebola and Marburg viruses.[3][4][5]

Like all things related to medicine, there is a lot of woo regarding viruses. Most commonly, said woo questions whether viruses are linked to certain diseases, how effective vaccines are in preventing virus infection, or even whether viruses can cause infection at all.

General features[edit]

There is some debate as to whether viruses are living organisms or not.[6][7] While they do contain genetic material (i.e. the DNA or RNA), and evolve, like any other living organism, they also contain no cell structures (things like a cytoplasm, cell wall, nucleus, et cetera), lack senses or a metabolism, and cannot reproduce independently.[8] The existence of giant viruses that can be "attacked" in the same way as a cell by smaller viruses has also led to some controversy regarding the definition of life, and whether viruses fit it.[7]

There are also other virus-like infectious agents like viroids, which are just strands of RNA without the protein coating and cause plant diseases, and prions, which are just protein particles and can cause, for example, degenerative disorders of the central nervous system like mad cow disease.

While the ability of viruses to infect cells is generally bad for health, there are some possible interesting applications in science and technology, like using viruses to reduce cancer.[9]

Damaged or weakened viruses are used in vaccination; they are processed by the immune system, which can then produce antibodies against the full-strength virus if later infected. Mutation of the virus may render past vaccines ineffective against new strains; viruses which frequently mutate in ways that alter their surface antigens such as influenza, the common cold and HIV have proven very difficult to effectively counter.

Since they are invisible and insidious, they play into many very basic human fears. However, viral disease can, for the most part, be contained by modern sanitary measures such as isolation, decontamination, and proper sanitary conditions. Gigantic death tolls are generally associated with ignorance about how disease is spread, improper application of procedures, or superstition and denialism overcoming medical consensus.

Antibiotics are ineffective in the treatment of viral infections, as they are designed instead to target bacteria. In fact, the use of antibiotics for viruses can even lead to the propagation of antibiotic resistant bacteria.[10]

Notable viruses[edit]

There are thousands of virus types of which we are aware and have studied, and thousands, or even millions more which we have yet to discover, with there being an estimated 320,000 new types of virus to be discovered just for mammals.[11][note 2] Here are a few notable ones.


See the main article on this topic: Smallpox

Smallpox is caused by a virus known as Variola Major, a member of the family poxviridae or poxviruses. Smallpox is a disease that only affects humans and likely first arose in agricultural Mesopotamian populations, at around 5000 BCE.[12] It is a very infectious disease that can be spread by breathing in infected droplets of saliva[13] While the average mortality rate is only about 30%,[14] this only led to the disease being even more infectious,[note 3] which, in turn, led to the disease killing several million people, with 300-500 million deaths observed in the 20th century alone.[15] It is notable in that it was the first infectious disease to be eradicated, due to a worldwide vaccination programme, with the last naturally occurring case being observed in Somalia, 1977.[14][note 4]


See the main article on this topic: AIDS

The human immunodeficiency virus (HIV) is known to cause the condition known as acquired immunodeficiency syndrome (AIDS)[16][17][18] which it achieves by damaging, destroying, or impeding the functioning of various T-helper cells in the immune system, particularly CD4+ cells.[16][18][19] Not everyone believes this, however, which leads to HIV denialism, which is strongly connected with alternative medicine practitioners and vaccine denialism.


Camp Funston, at Fort Riley, Kansas, during the 1918 flu pandemic

The influenza virus is best known for its astounding variety of mutations, as well as routinely causing pandemics during the 20th century (most notably, the Spanish flu killed between 50 and 100 million,[20] more than all deaths from World War I, which occurred concomitantly). It mutates very quickly, rendering current influenza vaccines useless within a year,[21] but since there remains a need for them, vaccines are reformulated every year. Theoretically, a universal flu vaccine that works against all flu types would eliminate or at least reduce the need for new vaccines.[22]

In modern days, most of the children who die of influenza are not vaccinated against it. Even after they recover from the flu, they are at risk of a secondary infection, which can be very dangerous.[23] The flu vaccine can reduce a child's risk of death.

Anti-vaccine groups have advocated the use of natural "remedies" over modern solutions like Tamiflu pills. At least one child who was denied modern medicine has died of influenza.[24]

GastroenteritisWikipedia is sometimes called "stomach flu", but is unrelated to the influenza virus.


See the main article on this topic: Ebola

The Ebola virus is known for its very short incubation period and its awesome lethality, exhibiting a death rate that can reach as high as 90%.[25] Fortunately, it is only infectious through the transmission of bodily fluids[26] — this means that it is relatively difficult to transmit, and is, despite its high lethality, unlikely to cause serious worldwide "apocalyptic" epidemics.


See the main article on this topic: COVID-19 pandemic

COVID-19 is a coronavirus, like SARS and MERS and some types of cold viruses. COVID-19 is highly infectious and infection potentially carries serious long-lasting effects.[27]

Viruses and evolution[edit]

Due to their rates of reproduction being incredibly fast, many viruses have been observed mutating and evolving at rates far faster than any (other) living thing — rates that are fast enough to be measured by humans.[28] Thus, viruses provide clear, observable empirical evidence of evolution through mutation and natural selection — proving once again that anyone who claims evolution is untrue because “we can’t see it happening” is simply wrong.[note 5]

Giant virusesWikipedia also possess large ramifications for our understanding of cellular evolution. These giant viruses, or "gliruses," possess traits that are strangely homologous to traits possessed by actual life[note 6] including possessing some of the genes encoding for translation.Wikipedia[29] This suggests that gliruses evolved from a cellular ancestor via a process of genome reduction.Wikipedia[29] Another hypothesis is that giant viruses evolved from smaller, simpler viruses that got more complex over time as they collected bits of genetic material from their hosts.[30]

See also[edit]


  1. The HIV virus, for example, is, on average, only ~145 nanometres in size, as explained here.
  2. And if that doesn't seem like a lot, consider all of the other forms of life on Earth that could serve to be viral hosts.
  3. As fewer patients died before transmitting the disease.
  4. In the mid 20th century, smallpox vaccination scars on the skin over the deltoid muscle were a common sight, more the rule than the exception.
  5. Of course, creationists can (and probably will) claim that this is only evidence of "microevolution", as evolution, according to creationists, only occurs within specific "kinds." This begs the question of what exactly the virus "kind" is, however, as there are multiple different types of virus (including the giant viruses mentioned below) that aren't (demonstrably) related to other viruses. Like the difference between RNA virusesWikipedia and DNA viruses.Wikipedia Are these two types of virus, who use completely separate genetic substrates, members of the same kind? Or are there kinds within kinds? What even is a "kind" if two groups of critters are completely separate from each other? We can demonstrate that all three domains of life are related to each other. We can't do the same thing for RNA and DNA viruses.
  6. Without delving into the quagmire that is the question "do viruses count as a form of life"?


  7. 7.0 7.1
  8. Rybicki, EP. The classification of organisms at the edge of life, or problems with virus systematics. S Afr J Sci. 1990;86:182–186.
  10. Why Don’t Antibiotics Kill Viruses?
  14. 14.0 14.1
  16. 16.0 16.1
  18. 18.0 18.1 [1]
  21. These changes happen often enough that your immune system can’t recognize the flu virus from year to year.
  22. Roberts, M. (2015, August 24). Universal flu vaccine comes closer, scientists say. BBC News
  23. CDC: Most Children Dying From Flu Not Vaccinated - Web MD
  24. Anti-Vax Facebook Group Told CO Mom to Give Son Elderberries Instead of Tamiflu. Days Later He Died.
  27. Coronavirus disease (COVID-19), World Health Organization 9 August 2023
  28. Stern, A. and Andino, R., 2016. Viral Evolution. Viral Pathogenesis, pp.233-240.
  29. 29.0 29.1 Legendre M, Arslan D, Abergel C, Claverie JM. Genomics of Megavirus and the elusive fourth domain of Life. Commun Integr Biol. 2012 Jan 1;5(1):102-6. doi: 10.4161/cib.18624. PMID: 22482024; PMCID: PMC3291303.
  30. In Giant Virus Genes, Hints About Their Mysterious Origin[a w]NPR