A 'virus' (from the
Latin noun ''virus'', meaning
toxin or
poison) is a sub-
microscopic particle (ranging in size from 20–300
nm) that can
infect the
cells of a
biological organism. Viruses can replicate themselves only by infecting a host cell. They therefore cannot reproduce on their own. At the most basic level, viruses consist of
genetic material contained within a protective
protein coat called a
capsid. They infect a wide variety of organisms: both
eukaryotes (animals, plants,
protists, and
fungi) and
prokaryotes (
bacteria and
archaea). A virus that infects bacteria is known as a ''
bacteriophage'', often shortened to ''phage''. The study of viruses is known as
virology and people who study viruses are known as virologists. Viruses cause several serious human diseases, such as
AIDS,
influenza and
rabies. Therapy is difficult for viral diseases as
antibiotics have no effect on viruses and few
antiviral drugs are known. The best way to prevent viral diseases is with a
vaccine, which produces
immunity.
It has been argued extensively whether viruses are living organisms. Most virologists consider them non-living,
[1][2][3] as they do not meet all the criteria of the generally accepted definition of
life. For example, unlike living organisms as defined, viruses do not respond to changes in the environment.
Discovery
Computer-generated image of virions
Viral diseases such as
rabies,
yellow fever and
smallpox have affected humans for many centuries. There is hieroglyphical evidence of
polio in the ancient Egyptian empire,
[ Polio Eradication Goal Extended, Lewis R, , , The Scientist, 2000 ] however, the cause of these diseases was unknown at the time. In 1717,
Mary Montagu, the wife of an English ambassador to the
Ottoman Empire, observed local women
inoculating their children against
smallpox.
[ The smallpox story: life and death of an old disease, Behbehani AM, , , Microbiol Rev, 1983 ] In the late 18th century,
Edward Jenner observed and studied Miss Sarah Nelmes, a milkmaid who had previously caught
cowpox and was subsequently found to be immune to
smallpox, a similar, but devastating virus. Jenner developed the first
vaccine based on these findings; after lengthy (but successful)
vaccination campaigns the
World Health Organization (WHO) certified the eradication of
smallpox in 1979.
[ Smallpox eradication: destruction of variola virus stocks ]
In the late 19th century
Charles Chamberland developed a porcelain filter with pores small enough to filter bacteria, yet retain all viable viruses.
[ The birth of virology, Horzinek MC, , , Antonie van Leeuwenhoek, 1997 ] Dimitri Ivanovski used this filter to study
tobacco mosaic virus. He published experiments showing that crushed leaf extracts of infected tobacco plants were still infectious after filtering through such filters. At about the same time, several others documented filterable disease-causing agents, with several independent experiments showing that viruses were different from bacteria, yet they could also cause disease in living organisms. These experiments showed that viruses are orders of magnitudes smaller than bacteria. The term ''virus'' was coined by the Dutch microbiologist
Martinus Beijerinck.
In the early 20th century,
Frederick Twort discovered that bacteria could be attacked by viruses.
Felix d'Herelle, working independently, showed that a preparation of viruses caused areas of cellular death on thin
cell cultures spread on
agar. Counting the dead areas allowed him to estimate the original number of viruses in the suspension. The invention of
Electron microscopy provided the first look at viruses. In 1935
Wendell Stanley crystallised the tobacco mosaic virus and found it to be mostly
protein. A short time later the virus was separated into protein and
nucleic acid parts. In 1939,
Max Delbrück and
E.L. Ellis demonstrated that, in contrast to cellular organisms, bacteriophage reproduce in "one step", rather than exponentially.
A major problem for early virologists was the inability to propagate viruses on sterile culture media, as is done with cellular microorganisms. This limitation required medical virologists to infect living animals with infectious material, which is dangerous. The first breakthrough came in 1931, when
Ernest William Goodpasture demonstrated the growth of
influenza and several other viruses in fertile chicken eggs. However, many viruses would not grow in chicken eggs, and a more flexible technique was needed for propagation of viruses. The solution came in 1949 when
John Franklin Enders,
Thomas H. Weller and
Frederick Chapman Robbins together developed a technique to grow
polio virus in cultures of living animal cells. Their methods have since been extended and applied to the growth of many viruses and other infectious agents that do not grow on sterile culture media.
Origins
The origins of modern viruses are not entirely clear. It may be that no single mechanism can account for all viruses. They do not
fossilize well, so
molecular techniques have been the most useful means of hypothesising how they arose. Research in
microfossil identification and molecular biology may yet discern fossil evidence dating to the
Archean or
Proterozoic eons. Two main hypotheses currently exist.
[4]
Small viruses with only a few genes may be runaway stretches of nucleic acid originating from the genome of a living organism. Their genetic material could have been derived from transferable genetic elements such as
plasmids or
transposons, which are prone to moving within, leaving, and entering genomes.
Viruses with larger genomes, such as
poxviruses, may have once been small cells which parasitised larger host cells. Over time, genes not required by their parasitic lifestyle would have been lost in a streamlining process known as ''retrograde-evolution'' or ''reverse-evolution''. The bacteria
Rickettsia and
Chlamydia are living cells that, like viruses, can only reproduce inside host cells. They lend credence to the streamlining hypothesis, as their parasitic lifestyle is likely to have caused the loss of genes that enabled them to survive outside a host cell.
It is hypothetically possible that viruses represent a primitive form of self replicating DNA and are a precursor to life as it is presently defined.
Other infectious particles which are even simpler in structure than viruses include
viroids,
satellites, and
prions.
Classification
In
taxonomy, the classification of viruses is rather difficult due to the lack of a fossil record and the dispute over whether they are living or non-living. They do not fit easily into any of the
domains of
biological classification and therefore classification begins at the
family rank. However, the domain name of
Acytota (without cells) has been suggested. This would place viruses on a par with the other domains of
Eubacteria,
Archaea, and
Eukarya. Not all families are currently classified into orders, nor all genera classified into families.
As an example of viral classification, the
chicken pox virus belongs to family ''
Herpesviridae'', subfamily ''
Alphaherpesvirinae'' and genus ''
Varicellovirus''. It remains unranked in terms of order. The general structure is as follows.
:
Order (''-virales'')
::
Family (''-viridae'')
:::
Subfamily (''-virinae'')
::::
Genus (''-virus'')
:::::
Species (''-virus'')
The
International Committee on Taxonomy of Viruses (ICTV) developed the current classification system and put in place guidelines that put a greater weighting on certain virus properties in order to maintain family uniformity. In determining order, taxonomists should consider the type of nucleic acid present, whether the nucleic acid is single- or double-stranded, and the presence or absence of an
envelope. After these three main properties, other characteristics can be considered: the type of host, the capsid shape, immunological properties and the type of disease it causes.
In addition to this classification system, the
Nobel Prize-winning biologist
David Baltimore devised the
Baltimore classification system. This places a virus into one of seven ''Groups'', which distinguish viruses based on their mode of replication and genome type. The ICTV classification system is used in conjunction with the Baltimore classification system in modern virus classification.
Structure
A complete virus particle, known as a 'virion', is little more than a
gene transporter, consisting in its simplest form of
nucleic acid surrounded by a protective coat of
protein called a
capsid. A capsid is composed of proteins encoded by the viral
genome and its shape serves as the basis for
morphological distinction. Virally coded protein subunits - sometimes called 'protomers' - will self-assemble to form the capsid, generally requiring the presence of the virus genome - however, many complex viruses code for proteins which assist in the construction of their capsid.
[ ] Proteins associated with nucleic acid are known as
nucleoproteins, and the association of viral capsid proteins with viral nucleic acid is called a 'nucleocapsid'.
In general, there are four main morphological virus types:
The range of sizes shown by viruses, relative to those of other organisms and
biomolecules
Size
To put viral size into perspective, a medium sized virion next to a flea is roughly equivalent to a human next to a mountain twice the size of
Mount Everest. Some
filoviruses have a total length of up to 1400 nm, however their capsid diameters are only about 80 nm. The majority of viruses which have been studied have a
capsid diameter between 10 and 300
nanometres. While most viruses are unable to be seen with a
light microscope, some are as large or larger than the smallest bacteria and can be seen under high optical magnification. More commonly, both scanning and transmission
electron microscopes are used to visualise virus particles.
A notable exception to the normal viral size range is the recently discovered
mimivirus, with a diameter of 750 nm which is larger than a ''
Mycoplasma'' bacterium.
[ Mycoplasma hominis: growth, reproduction, and isolation of small viable cells, Robertson J, Gomersall M, Gill P, , , J Bacteriol., 1975 ][ Mimivirus and the emerging concept of "giant" virus, Claverie J, Ogata H, Audic S, Abergel C, Suhre K, Fournier P, , , Virus Res, 2006 ] They also hold the record for the largest viral genome size, possessing about 1000 genes (some bacteria only possess 400) on a genome approximately 1.2
megabases in length.
[ The 1.2-megabase genome sequence of Mimivirus, Raoult D, Audic S, Robert C, ''et al'', , , Science, 2004 ] Their large genome also contains many genes which are
conserved in both prokaryotic and eukaryotic genes.
[6] The discovery of the virus has led many scientists to reconsider the controversial boundary between living organisms and viruses, which are currently considered as mere mobile genetic elements.
Genome
An enormous variety of genomic structures can be seen among viral species; as a group they contain more structural genomic diversity than the entire kingdoms of either plants, animals, or bacteria
[7].
Nucleic acid
A virus may employ either
DNA or
RNA as the nucleic acid. Rarely do they contain both, however
cytomegalovirus is an exception to this, possessing a DNA core with several
mRNA segments.
[ ] Plant viruses tend to have single-stranded RNA and bacteriophages tend to have double-stranded DNA.
[8] Some virus species possess abnormal
nucleotides, such as ''hydroxymethylcytosine'' instead of
cytosine, as a normal part of their genome.
[8]
Shape
Viral genomes may be circular, such as
polyomaviruses, or linear, such as
adenoviruses. The type of nucleic acid is irrelevant to the shape of the genome. Among
RNA viruses, the genome may be divided up into separate parts within the virion, or ''segmented''. All double-stranded RNA genomes, and some single-stranded RNA genomes, are segmented.
[ ] Each segment may code for one protein, and they are usually found together in one capsid. Not all segments are required to be in the same virion for the overall virus to be infectious, as demonstrated by the
brome mosaic virus.
[8]
Strandedness
A viral genome, irrespective of nucleic acid type, may be either single-stranded or double-stranded. Single-stranded genomes consist of an unpaired nucleic acid, analogous to one-half of a ladder split down the middle. Double-stranded genomes consist of 2 complimentary paired nucleic acids, analogous to a ladder. Some viruses, such as those belonging to the ''
Hepadnaviridae'', contain a genome which is partially double-stranded and partially single-stranded.
[11]
Sense
For viruses with RNA as their nucleic acid, the strands are said to be either
positive-sense (also called plus-strand) or
negative-sense (also called minus-strand) depending on whether it is complementary to viral mRNA. Positive-sense viral RNA is identical to viral mRNA and thus can be immediately
translated by the host cell. Negative-sense viral RNA is complementary to mRNA and thus must be converted to positive-sense RNA by an
RNA polymerase before translation. DNA nomenclature is similar to RNA nomenclature, in that the ''coding strand'' for the viral mRNA is complementary to it (-), and the ''non-coding strand'' is a copy of it (+).
Genome size
Genome size in terms of the weight of
nucleotides varies between species. The smallest genomes code for only four proteins and weigh about 10
6 daltons, while the largest weigh about 10
8 daltons and code for over one hundred proteins.
[ ] RNA viruses generally have smaller genome sizes than
DNA viruses due to a higher error-rate when replicating, resulting in a maximum upper size limit. Beyond this limit, too many errors in the genome when replicating render the virus useless or uncompetitive. In contrast, DNA viruses generally have larger genomes due to the high fidelity of their replication enzymes.
[11]
Replication
Viral populations do not grow through
cell division, because they are acellular; instead, they use the machinery and metabolism of a host cell to produce multiple copies of themselves. A virus can still cause degenerative effects within a cell without causing its death; collectively these are termed 'cytopathic effects'. Released virions can be passed between hosts through either direct contact, often via
body fluids, or through a
vector. In aqueous environments, viruses float free in the water.
Lytic or lysogenic
Viruses may have a
lytic or a
lysogenic cycle, with some viruses capable of carrying out both.
[ ]
Lytic cycle
In the lytic cycle, characteristic of virulent phages such as the
T4 phage, host cells will be induced by the virus to begin manufacturing the proteins necessary for virus reproduction. As well as proteins, the virus must also direct the replication of new genomes, the technique used for this varies greatly between virus species but depends heavily on the genome type. The final viral product is assembled spontaneously, though it may be aided by
molecular chaperones. After the genome has been replicated and the new capsid assembled, the virus causes the cell to be broken open (lysed) to release the virus particles. Some viruses do not lyse the cell but instead exit the cell via the
cell membrane in a process known as
exocytosis, taking a small portion of the membrane with them as a viral envelope. As soon as the cell is destroyed the viruses have to find a new host.
Lysogenic cycle
In contrast, the lysogenic cycle does not result in immediate lysing of the host cell, instead the viral genome integrates into the host DNA and replicates along with it. The virus remains dormant but after the host cell has replicated several times, or if environmental conditions permit it, the virus will become active and enter the lytic phase. The lysogenic cycle allows the host cell to continue to survive and reproduce, and the virus is passed on to all of the cell’s offspring.
A falsely coloured electron micrograph of multiple
bacteriophages
Bacteriophages
'
Bacteriophages' infect specific bacteria by binding to
surface receptor molecules and then enter the cell. Within a short amount of time, sometimes just minutes, bacterial
polymerase starts translating viral mRNA into protein. These proteins go on to become either new virions within the cell, helper proteins which help assembly of new virions, or proteins involved in cell
lysis. Viral enzymes aid in the breakdown of the cell membrane, and in the case of the
T4 phage, in just over twenty minutes after injection over three hundred phages will be released.
DNA viruses
Animal '
DNA viruses', such as
herpesviruses, enter the host via
endocytosis, the process by which cells take in material from the external environment. Frequently after a chance collision with an appropriate surface receptor on a cell, the virus penetrates the cell, the viral genome is released from the capsid and host polymerases begin transcribing viral mRNA. New virions are assembled and released either by cell lysis or by budding off the cell membrane.
RNA viruses
Animal '
RNA viruses' can be placed into about four different groups depending on their mode of replication. The
polarity of the RNA largely determines the replicative mechanism, as well as whether the genetic material is single-stranded or double-stranded. Some
RNA viruses are actually DNA based but use an RNA-intermediate to replicate. RNA viruses are heavily dependent upon virally encoded
RNA replicase to create copies of their genomes.
Reverse transcribing viruses
'
Reverse transcribing viruses' are viruses that replicate using reverse transcription, which is the formation of DNA from an RNA template. Those viruses containing RNA genomes use a DNA intermediate to replicate, whereas those containing DNA genomes use an RNA intermediate during genome replication. Both types of reverse transcribing viruses use the
reverse transcriptase enzyme to carry out the nucleic acid conversion.
Lifeform debate
Argument continues over whether viruses are truly alive. According to the
United States Code, they are considered
microorganisms in the sense of biological weaponry and malicious use. Scientists, however, are divided. Things become complicated as they look at simple viruses,
viroids and
prions. Viruses resemble other organisms in that they possess nucleic acid, and can respond - in infected cells - to their environment in a limited fashion. They can also reproduce by creating multiple copies of themselves through simple self-assembly.
Viruses do not have a
cell structure, regarded as the basic unit of life. Additionally, although they reproduce, they do not metabolise on their own and therefore require a host cell to replicate and synthesise new products. Bacterial species such as
Rickettsia and
Chlamydia, while living organisms, are even unable to reproduce outside of a host cell.
An argument can be made that all accepted forms of life use
cell division to reproduce, whereas all viruses spontaneously assemble within cells. The comparison is drawn between viral self-assembly and the autonomous growth of non-living
crystals. Virus self-assembly within host cells also has implications for the study of the
origin of life, as it lends credence to the hypothesis that life could have started as self-assembling organic molecules.
If viruses are considered alive, then the criteria specifying life will have been permanently changed, leading scientists to question what the basic prerequisite of life is. The standards required to call something artificially alive would be reduced and the prospect of creating
artificial life would be enhanced. If viruses were said to be alive, the question could follow of whether even smaller infectious particles, such as
viroids and
prions, are alive.
Viruses and disease
:''For more examples of diseases caused by viruses see
List of infectious diseases
Examples of common human diseases caused by viruses include the
common cold,
the flu,
chickenpox and
cold sores. Many serious diseases such as
Ebola,
AIDS,
avian flu and
SARS are also caused by viruses. The relative ability of viruses to cause disease is described in terms of
virulence. Other diseases are under investigation as to whether they too have a virus as the causative agent, such as the possible connection between
Human Herpesvirus Six (HHV6) and neurological diseases such as
multiple sclerosis and
chronic fatigue syndrome. Recently it was also shown that cervical cancer is partially caused by
papillomavirus, representing evidence in humans of a link existing between cancer and an infective agent.
[ Human Papilloma Virus ] There is current controversy over whether the
borna virus, previously thought of as causing
neurological disease in horses, could be responsible for
psychiatric illness in humans.
[ High seroprevalence of Borna virus infection in schizophrenic patients, family members and mental health workers in Taiwan, Chen C, Chiu Y, Wei F, Koong F, Liu H, Shaw C, Hwu H, Hsiao K, , , Mol Psychiatry, 1999 ]
Viruses have many different mechanisms by which they produce disease in an organism, which largely depends on the species. Mechanisms at the cellular level primarily include cell
lysis, the breaking open and subsequent death of the cell. In
multicellular organisms, if enough cells die the whole organism will start to suffer the effects. Although many viruses result in the disruption of healthy
homeostasis, resulting in disease, they may also exist relatively harmlessly within an organism. An example would include the ability of the
herpes simplex virus, which cause
coldsores, to remain in a dormant state within the human body.
Epidemics
A number of highly lethal viral pathogens are members of the
Filoviridae. Filoviruses are filament-like viruses that cause
viral hemorrhagic fever, and include the
Ebola and
Marburg viruses. The Marburg virus attracted widespread press attention in April 2005 for an outbreak in
Angola. Beginning in October 2004 and continuing into 2005, the outbreak was the world's worst epidemic of any kind of viral hemorrhagic fever.
[13]
Native American populations were devastated by contagious diseases, particularly
smallpox, brought to the Americas by European colonists. It is unclear how many Native Americans were killed by foreign diseases after the arrival of Columbus in the Americas, but the numbers have been estimated to be close to 70% of the indigenous population.
[14] The damage done by this disease may have significantly aided European attempts to displace or conquer the native population.
Detection, purification and diagnosis
In the laboratory, several techniques for growing and detecting viruses exist. Purification of viral particles can be achieved using
differential centrifugation,
isopycnic centrifugation, precipitation with
ammonium sulfate or
ethylene glycol, and removal of cell components from a homogenised cell mixture using
organic solvents or
enzymes to leave the virus particles in solution.
Assays to detect and quantify viruses include:
★
Hemagglutination assays, which quantitatively measure how many virus particles are in a solution of
red blood cells by the amount of
agglutination the viruses cause between them. This occurs as many viruses are able to bind to the surface of one or more red blood cells.
★ Direct counts using an
electron microscope. A dilute mixture of virus particles and beads of known size are sprayed onto a special sheet and examined under high magnification. The virions are counted and the number extrapolated to estimate the number of virions in the undiluted mixture.
★
Plaque assays involve growing a thin layer of host cells onto a culture dish and adding a dilute mixture of virions onto it. The virions will infect and kill the cells they land on, producing holes in the cell layer known as plaques. The number of plaques can be counted and the number of virions estimated from it.
Detection and subsequent isolation of new viruses from patients is a specialised laboratory subject. Normally it requires the use of large facilities, expensive equipment, and trained specialists such as technicians,
molecular biologists, and
virologists. Often, this effort is undertaken by state and national governments and shared internationally through organizations like the
World Health Organization.
Prevention and treatment
Because viruses use the machinery of a host cell to reproduce and also reside within them, they are difficult to eliminate without killing the host cell. The most effective
medical approaches to viral diseases so far are
vaccinations to provide resistance to infection, and drugs which treat the symptoms of viral infections. Patients often ask for, and
physicians often prescribe,
antibiotics. These are useless against viruses, and their misuse against viral infections is one of the causes of
antibiotic resistance in
bacteria. However, in life-threatening situations the prudent course of action is to begin a course of antibiotic treatment while waiting for test results to determine whether the patient's symptoms are caused by a virus or a bacterial infection.
Potential uses in therapy
Virotherapy uses viruses as vectors to treat various diseases, as they can specifically target cells and DNA. It shows promise in the treatment of cancer and as a method for gene therapy. Eastern European doctors have used
phage therapy as an alternative to antibiotics for some time and interest in this approach is increasing, due to the high level of
antibiotic resistance now found in some pathogenic bacteria.
[15]
Applications
Life sciences
Viruses are important to the study of
molecular and
cellular biology as they provide simple systems that can be used to manipulate and investigate the functions of cells. The study and use of viruses have provided valuable information about many aspects of cell biology. For example, viruses have simplified the study of
genetics and helped human understanding of the basic mechanisms of
molecular genetics, such as
DNA replication,
transcription,
RNA processing,
translation,
protein transport, and
immunology.
Geneticists regularly use viruses as
vectors to introduce genes into cells that they are studying. This is useful for making the cell produce a foreign substance, or to study the effect of introducing a new gene into the genome. In similar fashion,
virotherapy uses viruses as vectors to treat various diseases, as they can specifically target cells and DNA. It shows promising use in the treatment of cancer and in
gene therapy.
Materials science and nanotechnology
Current trends in nanotechnology promise to make much more versatile use of viruses. From the viewpoint of a materials scientist, viruses can be regarded as organic nanoparticles. Their surface carries specific tools designed to cross the barriers of their host cells. The size and shape of viruses, and the number and nature of the functional groups on their surface, is precisely defined. As such, viruses are commonly used in materials science as scaffolds for covalently linked surface modifications. A particular quality of viruses is that they can be tailored by directed evolution. The powerful techniques developed by life sciences are becoming the basis of engineering approaches towards nanomaterials, opening a wide range of applications far beyond biology and medicine.
[ Viruses as Building Blocks for Materials and Devices, Fischlechner M, Donath E, , , Angewandte Chemie International Edition, 2007 ]
In April 2006 scientists at the
Massachusetts Institute of Technology (MIT) created
nanoscale metallic wires using a
genetically-modified virus.
[16] The MIT team was able to use the virus to create a working
battery with an
energy density up to three times more than current materials. The potential exists for this technology to be used in
liquid crystals,
solar cells,
fuel cells, and other electronics in the future.
Weapons
The ability of viruses to cause devastating
epidemics in human societies has led to the concern that viruses could be weaponized for
biological warfare. Further concern was raised by the successful recreation of the infamous 1918 influenza virus in a laboratory.
[17] The
smallpox virus devastated numerous societies throughout history before its eradication. It currently exists in several secure laboratories in the world, and fears that it may be used as a weapon are not totally unfounded. The modern global human population has almost no established resistance to smallpox; if it were to be released, a massive loss of life could be sustained before the virus is brought under control.
Etymology
The word is from the
Latin ''virus'' referring to
poison and other noxious substances, first used in English in 1392.
[ virus ] ''Virulent'', from Latin ''virulentus'' "poisonous" dates to 1400.
[ virulent, a. ] A meaning of "agent that causes infectious disease" is first recorded in 1728,
before the discovery of viruses by the
Russian-
Ukrainian biologist Dmitry Ivanovsky in 1892. The adjective ''viral'' dates to 1948.
[ viral, a. ] Today, ''virus'' is used to describe the biological viruses discussed above and also as a
metaphor for other parasitically-reproducing things, such as
memes or
computer viruses (since 1972).
The
neologism 'virion' or viron is used to refer to a single infective viral particle.
The Latin word is from a
Proto-Indo-European root
★ "to melt away, to flow," used of foul or malodorous fluids. It is a cognate of
Sanskrit '' "poison",
Avestan ''viš-'' "poison", Greek ''ios'' "poison",
Old Church Slavonic ''višnja'' "cherry",
Old Irish ''fi'' "poison",
Welsh ''gwy'' "fluid"; Latin ''viscum'' (see
viscous) "sticky substance" is also from the same root.
The English plural form of ''virus'' is ''viruses''. No reputable dictionary gives any other form, including such "reconstructed" Latin plural forms as ''viri'' (which actually means ''men''), and no plural form appears in the Latin corpus (See
plural of virus). ''Virus'' does not have a traditional Latin plural because its original sense, ''poison'' is a
mass noun like the English word ''furniture'', and, as pointed out above, English use of ''virus'' to denote the agent of a disease predates the discovery that these agents are microscopic parasites and thus in principle countable.
Philosophy
Viruses have attracted attention of philosophers and critics because of their position at the margins of life and their unique method of propagation.
Susan Sontag argues that viruses have been used detrimentally as metaphors for social phenomena.
[18] Gilles Deleuze and
Félix Guattari use the virus as an example of
rhizomatic being because of its nomadic movement through host organisms. They note that viruses can be responsible for
"aparallel evolution", which they see as disruptive to arborescent phylogentic trees.
[19]
See also
★
List of viruses
★
Nanobes
★
Nanobacteria
★
Provirus
★
Transduction
★
Bioaerosol
★
Oncolytic virus
Footnotes
1. http://school.discovery.com/lessonplans/programs/understandingviruses/
2. http://www.tulane.edu/~dmsander/garryfavwebfaq.html
3. http://library.thinkquest.org/CR0212089/virus.htm
4. Microbiology, , L, Prescott, Wm. C. Brown Publishers, , 0-697-01372-3
5.
6.
7. Principles of Virology, , , Flinth, ASM Press, New York, , 1-55581-259-7
8.
9.
10.
11.
12.
13. Marburg outbreak worst recorded
14. Smallpox epidemic ravages Native Americans on the northwest coast of North America in the 1770s
15. Bacteriophage therapy: a revitalized therapy against bacterial infectious diseases, Matsuzaki S, Rashel M, Uchiyama J, ''et al'', , , J. Infect. Chemother., 2005
16.
17.
18. Sontag, Susan (1978). Illness as Metaphor. Farrar Straus & Giroux.
19. Deleuze, Gilles and Félix Guattari (1987) [1980]. ''A Thousand Plateaus''. University of Minnesota Press.
References
★
Icosahedral virus structure
★ Villarreal, Luis P. (2005). "Viruses and the Evolution of Life." Washington, ASM Press.
★
All the Virology on the WWW
★
University of Leicester online notes - Virus Structure
★
Chronic Active Human Herpesvirus-6 (HHV-6) Infection: A New Disease Paradigm
★ Gelderblom, Hans R. (1996).
41. Structure and Classification of Viruses in ''
Medical Microbiology 4th ed.'' Samuel Baron ed. The University of Texas Medical Branch at Galveston. ISBN 0-9631172-1-1
★ Radetsky, Peter (1994). ''The Invisible Invaders: Viruses and the Scientists Who Pursue Them.'' Backbay Books, ISBNs 0316732168 (hc), 0316732176 (pb).
★ Theiler, Max and Downs, W. G. (1973). ''The Arthropod-Borne Viruses of Vertebrates: An Account of the Rockefeller Foundation Virus Program 1951-1970''. Yale University Press.
★
External links
★
HIV - HIV/AIDS Research
★
Vaccine Research Center (VRC) - Information concerning vaccine research studies
★
Chart of viral pathogens which contribute to indoor air pollution
★
Viruses: The new cancer hunters - An IsraCast article on virotherapy
★
The Big Picture Book of Viruses - Pictures and general information on many viruses
★
Scientific American Magazine (October 2003 Issue) Tumor-Busting Viruses
★
Detailed genomic and bioinformatic information about Category A, B, and C priority pathogens at NIH-funded database.
★
Assorted information about Viruses
★
"A few good viruses", a feature story on how viruses are being 'hijacked' for the benfit of humanity.
''Cosmos Magazine'', by Hamish Clarke, 7 February 2007
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