Virus classification
Encyclopedia
Virus classification is the process of naming virus
es and placing them into a taxonomic
system. Similar to the classification systems used for cellular organisms
, virus classification is the subject of ongoing debate and proposals. This is mainly due to the pseudo-living nature of viruses, which are not yet definitively classified as living or non-living. As such, they do not fit neatly into the established biological classification
system in place for cellular organisms.
Viruses are mainly classified by phenotypic characteristics, such as morphology, nucleic acid
type, mode of replication, host organism
s, and the type of disease
they cause. Currently there are two main schemes used for the classification of viruses: the ICTV
system and Baltimore classification
system, which places viruses into one of seven groups. Accompanying this broad method of classification are specific naming conventions and further classification guidelines set out by the International Committee on Taxonomy of Viruses
.
began to devise and implement rules for the naming and classification of viruses early in the 1970s, an effort that continues to the present day. The ICTV is the only body charged by the International Union of Microbiological Societies
(IUMS) with the task of developing, refining, and maintaining a universal virus taxonomy. The system shares many features with the classification system of cellular organisms, such as taxon
structure. Viral classification starts at the level of order and follows as thus, with the taxon suffixes given in italics:
So far, six orders have been established by the ICTV: the Caudovirales, Herpesvirales, Mononegavirales, Nidovirales, Picornavirales, and Tymovirales. These orders span viruses with varying host ranges. Caudovirales
are tailed dsDNA (group I) bacteriophages, Herpesvirales contains large eukaryotic dsDNA viruses, Mononegavirales
includes non-segmented (-) strand ssRNA (Group V) plant and animal viruses, Nidovirales
is composed of (+) strand ssRNA (Group IV) viruses with vertebrate hosts, Picornavirales contains small (+) strand ssRNA viruses that infect a variety of plant, insect, and animal hosts, and Tymovirales contains monopartite ssRNA viruses that infect plants. Other variations occur between the orders, for example, Nidovirales are isolated for their differentiation in expressing structural and non-structural proteins separately. However, this system of nomenclature differs from other taxonomic codes on several points. A minor point is that names of orders and families are italicized, as in the ICBN. Most notably, species names generally take the form of [Disease] virus. The establishment of an order is based on the inference that the virus families contained within a single order have most likely evolved from a common ancestor. The majority of virus families remain unplaced. Currently (2009) 6 orders, 87 families, 19 subfamilies, 348 genera, and 2,288 species of virus have been defined.
Baltimore classification (first defined in 1971) is a classification system that places viruses into one of seven groups depending on a combination of their nucleic acid
(DNA
or RNA
), strandedness (single-stranded or double-stranded), Sense
, and method of replication
. Named after David Baltimore
, a Nobel Prize
-winning biologist, these groups are designated by Roman numerals
and discriminate viruses depending on their mode of replication, and genome type. Other classifications are determined by the disease caused by the virus or its morphology, neither of which are satisfactory due to different viruses either causing the same disease or looking very similar. In addition, viral structures are often difficult to determine under the microscope. Classifying viruses according to their genome
means that those in a given category will all behave in a similar fashion, offering some indication of how to proceed with further research. Viruses can be placed in one of the seven following groups:
's system of binomial nomenclature
to classify viruses into 3 groups under one order, Virales. They are placed as follows:
, number of capsomers. This classification was approved by the Provisional Committee on Nomenclature of Virus (PNVC) of the International Association of Microbiological Societies (1962). It is as follows:
for productive multiplication. Their nucleic acids have substantially distinct nucleotide sequences from either their helper virus or host. When a satellite subviral agent encodes the coat protein in which it is encapsulated, it is then called a satellite virus.
s, named for their description as "proteinaceous and infectious particles", lack any detectable (as of 2002) nucleic acids or virus-like particles. They resist inactivation procedures that normally affect nucleic acids.
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
es and placing them into a taxonomic
Alpha taxonomy
Alpha taxonomy is the discipline concerned with finding, describing and naming species of living or fossil organisms. This field is supported by institutions holding collections of these organisms, with relevant data, carefully curated: such institutes include natural history museums, herbaria and...
system. Similar to the classification systems used for cellular organisms
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
, virus classification is the subject of ongoing debate and proposals. This is mainly due to the pseudo-living nature of viruses, which are not yet definitively classified as living or non-living. As such, they do not fit neatly into the established biological classification
Biological classification
Biological classification, or scientific classification in biology, is a method to group and categorize organisms by biological type, such as genus or species. Biological classification is part of scientific taxonomy....
system in place for cellular organisms.
Viruses are mainly classified by phenotypic characteristics, such as morphology, nucleic acid
Nucleic acid
Nucleic acids are biological molecules essential for life, and include DNA and RNA . Together with proteins, nucleic acids make up the most important macromolecules; each is found in abundance in all living things, where they function in encoding, transmitting and expressing genetic information...
type, mode of replication, host organism
Host (biology)
In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...
s, and the type of disease
Disease
A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...
they cause. Currently there are two main schemes used for the classification of viruses: the ICTV
ICTV
ICTV can stand for*International Committee on Taxonomy of Viruses, a taxonomic organisation and the nomenclature code it produces*ICTV , a content distribution network for delivering the web-media experience through television...
system and Baltimore classification
Baltimore classification
The Baltimore classification, developed by David Baltimore, is a virus classification system that groups viruses into families, depending on their type of genome and their method of replication....
system, which places viruses into one of seven groups. Accompanying this broad method of classification are specific naming conventions and further classification guidelines set out by the International Committee on Taxonomy of Viruses
International Committee on Taxonomy of Viruses
The International Committee on Taxonomy of Viruses is a committee which authorizes and organizes the taxonomic classification of viruses. They have developed a universal taxonomic scheme for viruses and aim to describe all the viruses of living organisms. Members of the committee are considered to...
.
Virus species definition
Species form the basis for any biological classification system. The ICTV had adopted the principle that a virus species is a polythetic class of viruses that constitutes a replicating lineage and occupies a particular ecological niche.ICTV classification
The International Committee on Taxonomy of VirusesInternational Committee on Taxonomy of Viruses
The International Committee on Taxonomy of Viruses is a committee which authorizes and organizes the taxonomic classification of viruses. They have developed a universal taxonomic scheme for viruses and aim to describe all the viruses of living organisms. Members of the committee are considered to...
began to devise and implement rules for the naming and classification of viruses early in the 1970s, an effort that continues to the present day. The ICTV is the only body charged by the International Union of Microbiological Societies
International Union of Microbiological Societies
The Internation Union of Microbiological Societies or IUMS, founded in 1927 as the International Society of Microbiology, is now one of 27 Scientific Unions of the International Council of Science ....
(IUMS) with the task of developing, refining, and maintaining a universal virus taxonomy. The system shares many features with the classification system of cellular organisms, such as taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
structure. Viral classification starts at the level of order and follows as thus, with the taxon suffixes given in italics:
- OrderOrder (biology)In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
(-virales)- FamilyFamily (biology)In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
(-viridae)- Subfamily (-virinae)
- GenusGenusIn biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
(-virus)- SpeciesSpeciesIn biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
- Species
- Genus
- Subfamily (-virinae)
- Family
So far, six orders have been established by the ICTV: the Caudovirales, Herpesvirales, Mononegavirales, Nidovirales, Picornavirales, and Tymovirales. These orders span viruses with varying host ranges. Caudovirales
Caudovirales
The Caudovirales are an order of viruses also known as the tailed bacteriophages. Under the Baltimore classification scheme, the Caudovirales are group I viruses as they have double stranded DNA genomes, which can be anywhere from 18,000 base pairs to 500,000 base pairs in length...
are tailed dsDNA (group I) bacteriophages, Herpesvirales contains large eukaryotic dsDNA viruses, Mononegavirales
Mononegavirales
The order Mononegavirales is the taxonomic home of numerous related viruses. Members of the order that are commonly known are, for instance, Ebola virus, human respiratory syncytial virus, measles virus, mumps virus, Nipah virus, and rabies virus. All of these viruses cause significant disease in...
includes non-segmented (-) strand ssRNA (Group V) plant and animal viruses, Nidovirales
Nidovirales
The Nidovirales are an order of viruses with animal hosts. It includes the families Coronaviridae, Arterivirus and Roniviridae.-Virology:...
is composed of (+) strand ssRNA (Group IV) viruses with vertebrate hosts, Picornavirales contains small (+) strand ssRNA viruses that infect a variety of plant, insect, and animal hosts, and Tymovirales contains monopartite ssRNA viruses that infect plants. Other variations occur between the orders, for example, Nidovirales are isolated for their differentiation in expressing structural and non-structural proteins separately. However, this system of nomenclature differs from other taxonomic codes on several points. A minor point is that names of orders and families are italicized, as in the ICBN. Most notably, species names generally take the form of [Disease] virus. The establishment of an order is based on the inference that the virus families contained within a single order have most likely evolved from a common ancestor. The majority of virus families remain unplaced. Currently (2009) 6 orders, 87 families, 19 subfamilies, 348 genera, and 2,288 species of virus have been defined.
Baltimore classification
Nucleic acid
Nucleic acids are biological molecules essential for life, and include DNA and RNA . Together with proteins, nucleic acids make up the most important macromolecules; each is found in abundance in all living things, where they function in encoding, transmitting and expressing genetic information...
(DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
or RNA
RNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
), strandedness (single-stranded or double-stranded), Sense
Sense (molecular biology)
In molecular biology and genetics, sense is a concept used to compare the polarity of nucleic acid molecules, such as DNA or RNA, to other nucleic acid molecules...
, and method of replication
Viral replication
Viral replication is the term used by virologists to describe the formation of biological viruses during the infection process in the target host cells. Viruses must first get into the cell before viral replication can occur. From the perspective of the virus, the purpose of viral replication is...
. Named after David Baltimore
David Baltimore
David Baltimore is an American biologist, university administrator, and Nobel laureate in Physiology or Medicine. He served as president of the California Institute of Technology from 1997 to 2006, and is currently the Robert A. Millikan Professor of Biology at Caltech...
, a Nobel Prize
Nobel Prize
The Nobel Prizes are annual international awards bestowed by Scandinavian committees in recognition of cultural and scientific advances. The will of the Swedish chemist Alfred Nobel, the inventor of dynamite, established the prizes in 1895...
-winning biologist, these groups are designated by Roman numerals
Roman numerals
The numeral system of ancient Rome, or Roman numerals, uses combinations of letters from the Latin alphabet to signify values. The numbers 1 to 10 can be expressed in Roman numerals as:...
and discriminate viruses depending on their mode of replication, and genome type. Other classifications are determined by the disease caused by the virus or its morphology, neither of which are satisfactory due to different viruses either causing the same disease or looking very similar. In addition, viral structures are often difficult to determine under the microscope. Classifying viruses according to their genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
means that those in a given category will all behave in a similar fashion, offering some indication of how to proceed with further research. Viruses can be placed in one of the seven following groups:
DNA viruses
- Group I: viruses possess double-stranded DNA.
- Group II: viruses possess single-stranded DNA.
| Virus Family | Examples (common names) | Virion naked/enveloped |
Capsid Symmetry |
Nucleic acid type | Group |
|---|---|---|---|---|---|
| 1.Adenoviridae Adenoviridae Adenoviruses are medium-sized , nonenveloped icosahedral viruses composed of a nucleocapsid and a double-stranded linear DNA genome... |
Adenovirus, Infectious canine hepatitis virus | Naked | Icosahedral | ds | I |
| 2.Papillomaviridae Papillomaviridae Papillomaviridae is an ancient taxonomic family of non-enveloped DNA viruses, collectively known as papillomaviruses. Several hundred species of papillomaviruses, traditionally referred to as "types", have been identified infecting all carefully inspected birds and mammals, but also a small number... |
Papillomavirus | Naked | Icosahedral | ds circular | I |
| 3.Parvoviridae Parvoviridae The Parvoviridae family includes the smallest known viruses, and some of the most environmentally resistant. They were discovered during the 1960s and affect vertebrates and insects... |
Parvovirus B19, Canine parvovirus | Naked | Icosahedral | ss | II |
| 4.Herpesviridae Herpesviridae The Herpesviridae are a large family of DNA viruses that cause diseases in animals, including humans. The members of this family are also known as herpesviruses. The family name is derived from the Greek word herpein , referring to the latent, recurring infections typical of this group of viruses... |
Herpes simplex virus, varicella-zoster virus, cytomegalovirus, Epstein-Barr virus | Enveloped | Icosahedral | ds | I |
| 5.Poxviridae Poxviridae Poxviruses are viruses that can, as a family, infect both vertebrate and invertebrate animals.Four genera of poxviruses may infect humans: orthopox, parapox, yatapox, molluscipox.... |
Smallpox virus, cow pox virus, sheep pox virus, orf virus, monkey pox virus, vaccinia virus | Complex coats | Complex | ds | I |
| 6.Hepadnaviridae Hepadnaviridae Hepadnaviruses are a family of viruses which can cause liver infections in humans and animals. There are two recognized genera:*Genus Orthohepadnavirus; type species: Hepatitis B virus... |
Hepatitis B virus | Enveloped | Icosahedral | circular, partially ds | VII |
| 7.Polyomaviridae | Polyoma virus; JC virus (progressive multifocal leukoencephalopathy) | Naked | Icosahedral | ds circular | I |
| 8.Anelloviridae | Torque teno virus | Naked | Icosahedral | ss circular | II |
RNA viruses
- Group III: viruses possess double-stranded RNA genomes, e.g. rotavirusRotavirusRotavirus is the most common cause of severe diarrhoea among infants and young children, and is one of several viruses that cause infections often called stomach flu, despite having no relation to influenza. It is a genus of double-stranded RNA virus in the family Reoviridae. By the age of five,...
. These genomes are always segmented. - Group IV: viruses possess positive-sense single-stranded RNA genomes. Many well known viruses are found in this group, including the picornaviruses (which is a family of viruses that includes well-known viruses like Hepatitis A virus, enteroviruses, rhinoviruses, poliovirus, and foot-and-mouth virus), SARSSevere acute respiratory syndromeSevere Acute Respiratory Syndrome is a respiratory disease in humans which is caused by the SARS coronavirus . Between November 2002 and July 2003 an outbreak of SARS in Hong Kong nearly became a pandemic, with 8,422 cases and 916 deaths worldwide according to the WHO...
virus, hepatitis CHepatitis CHepatitis C is an infectious disease primarily affecting the liver, caused by the hepatitis C virus . The infection is often asymptomatic, but chronic infection can lead to scarring of the liver and ultimately to cirrhosis, which is generally apparent after many years...
virus, yellow feverYellow feverYellow fever is an acute viral hemorrhagic disease. The virus is a 40 to 50 nm enveloped RNA virus with positive sense of the Flaviviridae family....
virus, and rubellaRubellaRubella, commonly known as German measles, is a disease caused by the rubella virus. The name "rubella" is derived from the Latin, meaning little red. Rubella is also known as German measles because the disease was first described by German physicians in the mid-eighteenth century. This disease is...
virus. - Group V: viruses possess negative-sense single-stranded RNA genomes. The deadly EbolaEbolaEbola virus disease is the name for the human disease which may be caused by any of the four known ebolaviruses. These four viruses are: Bundibugyo virus , Ebola virus , Sudan virus , and Taï Forest virus...
and Marburg virusMarburg virusMarburg virus disease is the name for the human disease caused by any of the two marburgviruses Marburg virus and Ravn virus...
es are well known members of this group, along with influenza virus, measlesMeaslesMeasles, also known as rubeola or morbilli, is an infection of the respiratory system caused by a virus, specifically a paramyxovirus of the genus Morbillivirus. Morbilliviruses, like other paramyxoviruses, are enveloped, single-stranded, negative-sense RNA viruses...
, mumpsMumpsMumps is a viral disease of the human species, caused by the mumps virus. Before the development of vaccination and the introduction of a vaccine, it was a common childhood disease worldwide...
and rabiesRabiesRabies is a viral disease that causes acute encephalitis in warm-blooded animals. It is zoonotic , most commonly by a bite from an infected animal. For a human, rabies is almost invariably fatal if post-exposure prophylaxis is not administered prior to the onset of severe symptoms...
.
| Virus Family | Examples (common names) | Virion naked/enveloped |
Capsid Symmetry |
Nucleic acid type | Group |
|---|---|---|---|---|---|
| 1.Reoviridae Reoviridae Reoviridae is a family of viruses that can affect the gastrointestinal system and respiratory tract. Viruses in the family Reoviridae have genomes consisting of segmented, double-stranded RNA... |
Reovirus, Rotavirus Rotavirus Rotavirus is the most common cause of severe diarrhoea among infants and young children, and is one of several viruses that cause infections often called stomach flu, despite having no relation to influenza. It is a genus of double-stranded RNA virus in the family Reoviridae. By the age of five,... |
Naked | Icosahedral | ds | III |
| 2.Picornaviridae | Enterovirus Enterovirus Enteroviruses are a genus of ssRNA viruses associated with several human and mammalian diseases. Serologic studies have distinguished 66 human enterovirus serotypes on the basis of antibody neutralization tests. Additional antigenic variants have been defined within several of the serotypes on the... , Rhinovirus Rhinovirus Human rhinoviruses are the most common viral infective agents in humans and are the predominant cause of the common cold. Rhinovirus infection proliferates in temperatures between 33–35 °C , and this may be why it occurs primarily in the nose... , Hepatovirus Hepatovirus Hepatitis is a genus of viruses belonging to the family Picornaviridae. It encompasses the Hepatitis A with one unclassified virus.-External links:*... , Cardiovirus Cardiovirus Cardiovirus is a genus within the family Picornaviridae. The genus comprises two species: Encephalomyocarditis virus and Theilovirus... , Aphthovirus Aphthovirus Aphthovirus is a viral genus of the family Picornaviridae. Aphthoviruses infect vertebrates, and include the causative agent of foot-and-mouth disease. Foot-and-mouth disease virus is the prototypic member of the genus Aphthovirus... , Poliovirus Poliovirus Poliovirus, the causative agent of poliomyelitis, is a human enterovirus and member of the family of Picornaviridae.Poliovirus is composed of an RNA genome and a protein capsid. The genome is a single-stranded positive-sense RNA genome that is about 7500 nucleotides long. The viral particle is... , Parechovirus Parechovirus Parechovirus is a viral genus in the family Picornaviridae. The genus is composed of two species: Human parechovirus and Ljungan virus.-Taxonomy:... , Erbovirus Erbovirus Erbovirus is a viral genus of the Picornaviridae family. Viruses belonging to the Erbovirus genus have been isolated in horses with acute upper febrile respiratory disease... , Kobuvirus Kobuvirus Kobuvirus is a viral genus belonging to the family Picornaviridae. The genus is composed of three species, Aichi virus, Bovine kobuvirus and Porcine kobuvirus each possessing a single serotype... , Teschovirus Teschovirus The Teschovirus is a genus of the Picornaviridae family. This virus is responsible for the porcine enteroviral encephalomyelitis disease caused in pigs [1]. The Teschen disease which gave the name to the particular virus is a severe and fatal form of pig encephalomyelitis... , Coxsackie Coxsackie Coxsackie may refer to:* Coxsackie , New York* Coxsackie , New York* Coxsackievirus -- any of a group of 23 Coxsackie A viruses and 6 Coxsackie B viruses.... |
Naked | Icosahedral | ss | IV |
| 3.Caliciviridae Caliciviridae The Caliciviridae family are a family of viruses, members of Class IV of the Baltimore scheme. They are positive-sense, single stranded RNA which is non-segmented. The caliciviruses have been found in a number of organisms such as humans, cattle, pigs, cats, chickens, reptiles, dolphins and... |
Norwalk virus, Hepatitis E Hepatitis E Hepatitis E is a viral hepatitis caused by infection with a virus called hepatitis E virus . HEV is a positive-sense single-stranded RNA icosahedral virus with a 7.5 kilobase genome. HEV has a fecal-oral transmission route. It is one of five known hepatitis viruses: A, B, C, D, and E... virus |
Naked | Icosahedral | ss | IV |
| 4.Togaviridae Togaviridae The Togaviridae are a family of viruses, including the following genera:* Genus Alphavirus; type species: Sindbis virus, Eastern equine encephalitis virus, Western equine encephalitis virus, Venezuelan equine encephalitis virus, Ross River virus, O'nyong'nyong virus, Chikungunya* Genus Rubivirus;... |
Rubella virus Rubella virus Rubella virus is the pathogenic agent of the disease Rubella, and is the cause of congenital rubella syndrome when infection occurs during the first weeks of lunacy.Humans are the only known host of this virus.... |
Enveloped | Icosahedral | ss | IV |
| 5.Arenaviridae | Lymphocytic choriomeningitis virus | Enveloped | Complex | ss(-) | V |
| 6.Flaviviridae Flaviviridae The Flaviviridae are a family of viruses that are primarily spread through arthropod vectors . The family gets its name from Yellow Fever virus, a type virus of Flaviviridae; flavus means yellow in Latin... |
Dengue virus Dengue virus Dengue virus in one of four serotypes is the cause of dengue fever. It is a mosquito-borne single positive-stranded RNA virus of the family Flaviviridae; genus Flavivirus... , Hepatitis C Hepatitis C Hepatitis C is an infectious disease primarily affecting the liver, caused by the hepatitis C virus . The infection is often asymptomatic, but chronic infection can lead to scarring of the liver and ultimately to cirrhosis, which is generally apparent after many years... virus, Yellow fever virus |
Enveloped | Icosahedral | ss | IV |
| 7.Orthomyxoviridae Orthomyxoviridae The Orthomyxoviridae are a family of RNA viruses that includes five genera: Influenzavirus A, Influenzavirus B, Influenzavirus C, Isavirus and Thogotovirus. A sixth has recently been described... |
Influenzavirus A Influenzavirus A Influenza A virus causes influenza in birds and some mammals and is the only species of Influenzavirus A. Influenzavirus A is a genus of the Orthomyxoviridae family of viruses. Strains of all subtypes of influenza A virus have been isolated from wild birds, although disease is uncommon... , Influenzavirus B Influenzavirus B Influenzavirus B is a genus in the virus family Orthomyxoviridae. The only species in this genus is called "Influenza B virus".Influenza B viruses are only known to infect humans and seals, giving them influenza... , Influenzavirus C Influenzavirus C Influenzavirus C is a genus in the virus family Orthomyxoviridae, which includes those viruses which cause influenza. The only species in this genus is called "Influenza C virus".Influenza C viruses are known to infect humans and pigs, giving them influenza... , Isavirus, Thogotovirus Thogotovirus Thogotovirus is a genus in the virus family Orthomyxoviridae. It can replicate in both tick cells and vertebrate cells and is usually transmitted by ticks.... |
Enveloped | Helical | ss(-) | V |
| 8.Paramyxoviridae | Measles virus, Mumps virus Mumps virus Mumps virus is the causative agent of mumps, a well-known common childhood disease characterised by swelling of the parotid glands and other epithelial tissues, causing high morbidity and in some cases more serious complications such as deafness... , Respiratory syncytial virus, Rinderpest virus, Canine distemper virus |
Enveloped | Helical | ss(-) | V |
| 9.Bunyaviridae Bunyaviridae Bunyaviridae is a family of negative-stranded RNA viruses. Though generally found in arthropods or rodents, certain viruses in this family occasionally infect humans. Some of them also infect plants.... |
California encephalitis virus California encephalitis virus California encephalitis virus was discovered in Kern County, California and causes encephalitis in humans. Encephalitis is an acute inflammation of the brain that can cause minor symptoms, such as headaches, to more severe symptoms such as seizures... , Hantavirus Hantavirus Hantaviruses are negative sense RNA viruses in the Bunyaviridae family. Humans may be infected with hantaviruses through rodent bites, urine, saliva or contact with rodent waste products... |
Enveloped | Helical | ss(-) | V |
| 10.Rhabdoviridae Rhabdoviridae Rhabdoviruses are viruses belonging to the family Rhabdoviridae, which is in the order Mononegavirales. The name is derived from the Greek rhabdos meaning rod referring to the shape of the viral particles. Rhabdoviruses infect a broad range of hosts throughout the animal and plant kingdoms... |
Rabies virus Rabies virus The rabies virus is neurotropic virus that causes fatal disease in human and animals. Rabies transmission can occur through the saliva of animals.... |
Enveloped | Helical | ss(-) | V |
| 11.Filoviridae Filoviridae The family Filoviridae is the taxonomic home of several related viruses that form filamentous virions. Two members of the family that are commonly known are Ebola virus and Marburg virus. Both viruses, and some of their lesser known relatives, cause severe disease in humans and nonhuman primates in... |
Ebola virus Ebola virus Ebola virus causes severe disease in humans and in nonhuman primates in the form of viral hemorrhagic fever. EBOV is a Select Agent, World Health Organization Risk Group 4 Pathogen , National Institutes of Health/National Institute of Allergy and Infectious Diseases Category A Priority Pathogen,... , Marburg virus Marburg virus Marburg virus disease is the name for the human disease caused by any of the two marburgviruses Marburg virus and Ravn virus... |
Enveloped | Helical | ss(-) | V |
| 12.Coronaviridae Coronaviridae Coronaviruses are enveloped, single-stranded, positive-sense RNA viruses with club-shaped surface about 120-160 nm in diameter that resemble a “corona”.-Virology:... |
Corona virus | Enveloped | Helical | ss | IV |
| 13.Astroviridae | Astrovirus Astrovirus Astrovirus is a type of virus that was first discovered in 1975 using electron microscopes following an outbreak of diarrhoea in humans. In addition to humans, astroviruses have now been isolated from numerous mammalian animal species and from avian species such as ducks, chickens, and turkey... |
Naked | Icosahedral | ss | IV |
| 14.Bornaviridae | Borna disease virus | Enveloped | Helical | ss(-) | V |
| 15.Arteriviridae | Arterivirus Arterivirus Arterivirus is a genus of virus, with type species equine arteritis virus. In 1996, the family Arteriviridae was included within the order Nidovirales. Arteriviruses are small, enveloped, animal viruses with an icosahedral core containing a positive-sense RNA genome... , Equine Arteritis Virus |
Enveloped | Icosahedral | ss | IV |
Reverse transcribing viruses
- Group VI: viruses possess single-stranded RNA genomes and replicate using reverse transcriptaseReverse transcriptaseIn the fields of molecular biology and biochemistry, a reverse transcriptase, also known as RNA-dependent DNA polymerase, is a DNA polymerase enzyme that transcribes single-stranded RNA into single-stranded DNA. It also helps in the formation of a double helix DNA once the RNA has been reverse...
. The retrovirusRetrovirusA retrovirus is an RNA virus that is duplicated in a host cell using the reverse transcriptase enzyme to produce DNA from its RNA genome. The DNA is then incorporated into the host's genome by an integrase enzyme. The virus thereafter replicates as part of the host cell's DNA...
es are included in this group, of which HIVHIVHuman immunodeficiency virus is a lentivirus that causes acquired immunodeficiency syndrome , a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive...
is a member. - Group VII: viruses possess double-stranded DNA genomes and replicate using reverse transcriptaseReverse transcriptaseIn the fields of molecular biology and biochemistry, a reverse transcriptase, also known as RNA-dependent DNA polymerase, is a DNA polymerase enzyme that transcribes single-stranded RNA into single-stranded DNA. It also helps in the formation of a double helix DNA once the RNA has been reverse...
. The hepatitis B virus can be found in this group.
Holmes classification
Holmes (1948) used Carolus LinnaeusCarolus Linnaeus
Carl Linnaeus , also known after his ennoblement as , was a Swedish botanist, physician, and zoologist, who laid the foundations for the modern scheme of binomial nomenclature. He is known as the father of modern taxonomy, and is also considered one of the fathers of modern ecology...
's system of binomial nomenclature
Binomial nomenclature
Binomial nomenclature is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, although they can be based on words from other languages...
to classify viruses into 3 groups under one order, Virales. They are placed as follows:
- Group I: PhaginaeBacteriophageA bacteriophage is any one of a number of viruses that infect bacteria. They do this by injecting genetic material, which they carry enclosed in an outer protein capsid...
(attacks bacteria) - Group II: Phytophaginae (attacks plants)
- Group III: Zoophaginae (attacks animals)
LHT System of Virus Classification
The LHT System of Virus Classification is based on chemical and physical characters like nucleic acid (DNA or RNA), Symmetry (Helical or Icosahedral or Complex), presence of envelope, diameter of capsidCapsid
A capsid is the protein shell of a virus. It consists of several oligomeric structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or may not correspond to individual proteins, are called capsomeres. The capsid encloses the genetic...
, number of capsomers. This classification was approved by the Provisional Committee on Nomenclature of Virus (PNVC) of the International Association of Microbiological Societies (1962). It is as follows:
- Phylum Vira (divided into 2 subphyla)
- Subphylum Deoxyvira (DNA viruses)
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- Class Deoxybinala (dual symmetry)
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- Order Urovirales
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- Family Phagoviridae
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- Class Deoxyhelica (Helical symmetry)
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- Order Chitovirales
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- Family Poxviridae
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- Class Deoxycubica (cubical symmetry)
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- Order Peplovirales
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- Family Herpesviridae (162 capsomeres)
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- Order Haplovirales (no envelope)
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- Family Iridoviridae (812 capsomeres)
- Family Adenoviridae (252 capsomeres)
- Family Papiloviridae (72 capsomeres)
- Family Paroviridae (32 capsomeres)
- Family Microviridae (12 capsomeres)
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- Subphylum Ribovira (RNA viruses)
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- Class Ribocubica
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- Order Togovirales
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- Family Arboviridae
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- Order Lymovirales
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- Family Napoviridae
- Family Reoviridae
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- Class Ribohelica
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- Order Sagovirales
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- Family Stomataviridae
- Family Paramyxoviridae
- Family Myxoviridae
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- Order Rhabdovirales
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- Suborder Flexiviridales
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- Family Mesoviridae
- Family Peptoviridae
- Suborder Rigidovirales
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- Family Pachyviridae
- Family Protoviridae
- Family Polichoviridae
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Subviral agents
The following agents are smaller than viruses but have some of their properties.Viroids
- Family AvsunviroidaeAvsunviroidaeThe Avsunviroidae are a family of viroids. At present three members are known of. They consist of RNA genomes between 246-375 nucleotides in length. They are single stranded covalent circles and have intramolecular base pairing. All members lack a central conserved region.-Replication:Replication...
- Genus Avsunviroid; type species: Avocado sunblotch viroidAvocado sunblotch viroidAvocado sunblotch viroid is an important disease affecting avocado trees.Infections result in lower yields and poorer quality fruit. ASBV is the smallest known viroid that infects plants and is transmitted by pollen and infected seeds or budwood....
- Genus Pelamoviroid; type species: Peach latent mosaic viroidPeach latent mosaic viroidPeach latent mosaic viroid is a type species from the genus Pelamoviroid, which belongs to the family Avsunviroidae. This family is characterized as having chloroplastic viroids with hammerhead ribozymes. Peach latent mosaic viroid is a 336-351nt circular RNA which has a branched formation. This...
- Genus Elaviroid; type species: Eggplant latent viroid'
- Genus Avsunviroid; type species: Avocado sunblotch viroid
- Family PospiviroidaePospiviroidaeThe Pospiviroidae are a family of viroids, including the first viroid to be discovered, PSTVd. Their secondary structure is key to their biological activity. The classification of this family is based on differences in the conserved central region sequence...
- Genus PospiviroidPospiviroidPospiviroid is a genus of viroid which most commonly infects tubers. It belongs to the family pospiviroidae.The first viroid discovered was a pospiviroid, the PSTVd species ....
; type species: Potato spindle tuber viroidPotato spindle tuber viroidThe Potato spindle tuber viroid was the first viroid to be identified. PSTVd is a small, circular RNA molecule closely related to the Chrysanthemum stunt viroid. Present within the viroidal RNA is the Pospiviroid RY motif stem loop. The natural hosts are potatoes and tomatoes... - Genus HostuviroidHostuviroidHostuviroid is a genus of viroids that includes the hop stunt viroids, a group of viroids that infects many different types of plants, including the common hop plant.Some hostuviroids:Citrus gummy bark viroidGrapevine viroid...
; type species: Hop stunt viroidHop stunt viroidThe hop stunt viroid is a viroid species that infects the common hop plant, citrus plants and grapevines, among others. It is a member of the Pospiviroidae family and the Hostuviroid genus.... - Genus Cocadviroid; type species: Coconut cadang-cadang viroid
- Genus Apscaviroid; type species: Apple scar skin viroid
- Genus Coleviroid; type species: Coleus blumei viroid 1
- Genus Pospiviroid
Satellites
Satellites depend on co-infection of a host cell with a helper virusHelper virus
A helper virus is a virus used when producing copies of a helper dependent viral vector which does not have the ability to replicate on its own. The helper virus is used to coinfect cells alongside the viral vector and provides the necessary enzymes for replication of the genome of the viral vector....
for productive multiplication. Their nucleic acids have substantially distinct nucleotide sequences from either their helper virus or host. When a satellite subviral agent encodes the coat protein in which it is encapsulated, it is then called a satellite virus.
- Satellite viruses
- Single-stranded RNA satellite viruses
- Subgroup 1: Chronic bee-paralysis satellite virus
- Subgroup 2: Tobacco necrosis satellite virusTobacco necrosis virusTobacco necrosis virus is a plant virus of the family Tombusviridae.It is transmitted by the fungus Olpidium brassicae.-General Properties of TNV:TNV has wide host range . The virus can be isolated from roots of...
- Single-stranded RNA satellite viruses
- Satellite nucleic acids
- Single-stranded satellite DNAs
- Double-stranded satellite RNAs
- Single-stranded satellite RNAs
- Subgroup 1: Large satellite RNAs
- Subgroup 2: Small linear satellite RNAs
- Subgroup 3: Circular satellite RNAs (virusoidVirusoidVirusoids are circular single-stranded RNAs dependent on plant viruses for replication and encapsidation. The genome of virusoids consist of several hundred nucleotides and only encodes structural proteins....
s)
Prions
PrionPrion
A prion is an infectious agent composed of protein in a misfolded form. This is in contrast to all other known infectious agents which must contain nucleic acids . The word prion, coined in 1982 by Stanley B. Prusiner, is a portmanteau derived from the words protein and infection...
s, named for their description as "proteinaceous and infectious particles", lack any detectable (as of 2002) nucleic acids or virus-like particles. They resist inactivation procedures that normally affect nucleic acids.
- Mammalian prions:
- Agents of spongiform encephalopathiesTransmissible spongiform encephalopathyTransmissible spongiform encephalopathies , also known as prion diseases, are a group of progressive conditions that affect the brain and nervous system of many animals, including humans. According to the most widespread hypothesis they are transmitted by prions, though some other data suggest an...
- Agents of spongiform encephalopathies
- Fungal prionsFungal prionsFungal prions provide an excellent model for the understanding of disease-forming mammalian prions. Fungal prions are naturally occurring proteins that can undergo a structural conversion that becomes self-propagating and infectious. They represent an epigenetic phenomenon in which information is...
:- PSI+ prion of Saccharomyces cerevisiaeSaccharomyces cerevisiaeSaccharomyces cerevisiae is a species of yeast. It is perhaps the most useful yeast, having been instrumental to baking and brewing since ancient times. It is believed that it was originally isolated from the skin of grapes...
- URE3 prion of Saccharomyces cerevisiaeSaccharomyces cerevisiaeSaccharomyces cerevisiae is a species of yeast. It is perhaps the most useful yeast, having been instrumental to baking and brewing since ancient times. It is believed that it was originally isolated from the skin of grapes...
- RNQ/PIN+ prion of Saccharomyces cerevisiaeSaccharomyces cerevisiaeSaccharomyces cerevisiae is a species of yeast. It is perhaps the most useful yeast, having been instrumental to baking and brewing since ancient times. It is believed that it was originally isolated from the skin of grapes...
- Het-s prion of Podospora anserina
- PSI+ prion of Saccharomyces cerevisiae
See also
- Binomial nomenclatureBinomial nomenclatureBinomial nomenclature is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, although they can be based on words from other languages...
- International Committee on Taxonomy of VirusesInternational Committee on Taxonomy of VirusesThe International Committee on Taxonomy of Viruses is a committee which authorizes and organizes the taxonomic classification of viruses. They have developed a universal taxonomic scheme for viruses and aim to describe all the viruses of living organisms. Members of the committee are considered to...
- List of viruses
- Nomenclature CodesNomenclature CodesNomenclature codes or codes of nomenclature are the various rulebooks that govern biological taxonomic nomenclature, each in their own broad field of organisms...
- Biological classificationBiological classificationBiological classification, or scientific classification in biology, is a method to group and categorize organisms by biological type, such as genus or species. Biological classification is part of scientific taxonomy....
- TaxonomyTaxonomyTaxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
- Trinomial nomenclatureTrinomial nomenclatureIn biology, trinomial nomenclature refers to names for taxa below the rank of species. This is different for animals and plants:* for animals see trinomen. There is only one rank allowed below the rank of species: subspecies....
- VirologyVirologyVirology is the study of viruses and virus-like agents: their structure, classification and evolution, their ways to infect and exploit cells for virus reproduction, the diseases they cause, the techniques to isolate and culture them, and their use in research and therapy...
- List of genera of viruses