A viral disease (or viral infection) occurs when an organism's body is invaded by pathogenic

virus A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsky's ...

es, and

infectious An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dis ...

virus particles (virions) attach to and enter susceptible cells.

Structural Characteristics

Basic structural characteristics, such as genome type, virion shape and replication site, generally share the same features among virus species within the same family. * Double-stranded DNA families: three are non-enveloped (''

Adenoviridae Adenoviruses (members of the family ''Adenoviridae'') are medium-sized (90–100 nm), nonenveloped (without an outer lipid bilayer) viruses with an icosahedral nucleocapsid containing a double-stranded DNA genome. Their name derives from ...

'', ''

Papillomaviridae ''Papillomaviridae'' is a family of non- enveloped DNA viruses whose members are known as papillomaviruses. Several hundred species of papillomaviruses, traditionally referred to as "types", have been identified infecting all carefully inspected ...

'' and '' Polyomaviridae'') and two are enveloped (''

Herpesviridae ''Herpesviridae'' is a large family of DNA viruses that cause infections and certain diseases in animals, including humans. The members of this family are also known as herpesviruses. The family name is derived from the Greek word ''ἕρπειν ...

'' and ''

Poxviridae ''Poxviridae'' is a family of double-stranded DNA viruses. Vertebrates and arthropods serve as natural hosts. There are currently 83 species in this family, divided among 22 genera, which are divided into two subfamilies. Diseases associated ...

''). All of the non-enveloped families have icosahedral

capsids A capsid is the protein shell of a virus, enclosing its genetic material. It consists of several oligomeric (repeating) structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or may ...

. * Partly

double-stranded DNA viruses A DNA virus is a virus that has a genome made of deoxyribonucleic acid (DNA) that is replicated by a DNA polymerase. They can be divided between those that have two strands of DNA in their genome, called double-stranded DNA (dsDNA) viruses, and ...

: ''

Hepadnaviridae ''Hepadnaviridae'' is a family of viruses. Humans, apes, and birds serve as natural hosts. There are currently 18 species in this family, divided among 5 genera. Its best-known member is hepatitis B virus. Diseases associated with this family i ...

''. These viruses are enveloped. * One family of

single-stranded DNA viruses A DNA virus is a virus that has a genome made of deoxyribonucleic acid (DNA) that is replicated by a DNA polymerase. They can be divided between those that have two strands of DNA in their genome, called double-stranded DNA (dsDNA) viruses, and ...

infects humans: ''

Parvoviridae Parvoviruses are a family of animal viruses that constitute the family ''Parvoviridae''. They have linear, single-stranded DNA (ssDNA) genomes that typically contain two genes encoding for a replication initiator protein, called NS1, and the p ...

''. These viruses are non-enveloped. * Positive single-stranded

RNA Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...

families: three non-enveloped (''

Astroviridae ''Astroviridae'' is a family of non-enveloped ssRNA viruses that cause infections in different animals. The family name is derived from the Greek word ''astron'' ("star") referring to the star-like appearance of spikes projecting from the surface ...

'', '' Caliciviridae'' and ''

Picornaviridae Picornaviruses are a group of related nonenveloped RNA viruses which infect vertebrates including fish, mammals, and birds. They are viruses that represent a large family of small, positive-sense, single-stranded RNA viruses with a 30 nm i ...

'') and four enveloped ('' Coronaviridae'', ''

Flaviviridae ''Flaviviridae'' is a family of enveloped positive-strand RNA viruses which mainly infect mammals and birds. They are primarily spread through arthropod vectors (mainly ticks and mosquitoes). The family gets its name from the yellow fever virus ...

'', ''

Retroviridae A retrovirus is a type of virus that inserts a DNA copy of its RNA genome into the DNA of a host cell that it invades, thus changing the genome of that cell. Once inside the host cell's cytoplasm, the virus uses its own reverse transcriptase ...

'' and ''

Togaviridae This category is for articles about virus families (or redirects to such articles). There should be no subcategories. families Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity ( ...

''). All the non-enveloped families have icosahedral nucleocapsids. * Negative single-stranded RNA families: '' Arenaviridae'', ''

Bunyaviridae ''Bunyavirales'' is an order of segmented negative-strand RNA viruses with mainly tripartite genomes. Member viruses infect arthropods, plants, protozoans, and vertebrates. It is the only order in the class ''Ellioviricetes''. The name ''Bunyavir ...

'', ''

Filoviridae ''Filoviridae'' () is a family of single-stranded negative-sense RNA viruses in the order ''Mononegavirales''. Two members of the family that are commonly known are Ebola virus and Marburg virus. Both viruses, and some of their lesser known re ...

'', ''

Orthomyxoviridae ''Orthomyxoviridae'' (from Greek ὀρθός, ''orthós'' 'straight' + μύξα, ''mýxa'' ' mucus') is a family of negative-sense RNA viruses. It includes seven genera: '' Alphainfluenzavirus'', '' Betainfluenzavirus'', '' Gammainfluenzavirus' ...

'',

Paramyxoviridae ''Paramyxoviridae'' (from Greek ''para-'' “by the side of” and ''myxa'' “ mucus”) is a family of negative-strand RNA viruses in the order ''Mononegavirales''. Vertebrates serve as natural hosts. Diseases associated with this family inclu ...

'' and ''

Rhabdoviridae ''Rhabdoviridae'' is a family of negative-strand RNA viruses in the order ''Mononegavirales''. Vertebrates (including mammals and humans), invertebrates, plants, fungi and protozoans serve as natural hosts. Diseases associated with member vir ...

''. All are enveloped with helical nucleocapsids. * Double-stranded RNA genome: ''

Reoviridae ''Reoviridae'' is a family of double-stranded RNA viruses. Member viruses have a wide host range, including vertebrates, invertebrates, plants, protists and fungi. They lack lipid envelopes and package their segmented genome within multi-layer ...

''. * The

Hepatitis D virus Hepatitis D is a type of viral hepatitis caused by the hepatitis delta virus (HDV). HDV is one of five known hepatitis viruses: A, B, C, D, and E. HDV is considered to be a satellite (a type of subviral agent) because it can propagate only in ...

has not yet been assigned to a family, but is clearly distinct from the other families infecting humans. * Viruses known to infect humans that have not been associated with disease: the family ''

Anelloviridae ''Anelloviridae'' is a family of viruses. They are classified as vertebrate viruses and have a non-enveloped capsid, which is round with isometric, icosahedral symmetry and has a triangulation number of 3. The name is derived from Italian ''anel ...

'' and the genus '' Dependovirus''. Both of these taxa are non-enveloped single-stranded DNA viruses.

Pragmatic Rules

Human-infecting virus families offer rules that may assist physicians and medical

microbiologists A microbiologist (from Greek ) is a scientist who studies microscopic life forms and processes. This includes study of the growth, interactions and characteristics of microscopic organisms such as bacteria, algae, fungi, and some types of par ...

/ virologists. As a general rule, DNA viruses replicate within the

cell nucleus The cell nucleus (pl. nuclei; from Latin or , meaning ''kernel'' or ''seed'') is a membrane-bound organelle found in eukaryotic cells. Eukaryotic cells usually have a single nucleus, but a few cell types, such as mammalian red blood cells, h ...

while RNA viruses replicate within the

cytoplasm In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. Th ...

. Exceptions are known to this rule: poxviruses replicate within the cytoplasm and orthomyxoviruses and hepatitis D virus (RNA viruses) replicate within the nucleus. * Segmented genomes: ''

'', ''

'', '' Arenaviridae'', and ''

'' (acronym BOAR). All are RNA viruses. * Viruses transmitted almost exclusively by

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chitin, o ...

s: ''Bunyavirus'', ''

Flavivirus ''Flavivirus'' is a genus of positive-strand RNA viruses in the family '' Flaviviridae''. The genus includes the West Nile virus, dengue virus, tick-borne encephalitis virus, yellow fever virus, Zika virus and several other viruses which may ca ...

'', and ''

Togavirus ''Alphavirus'' is a genus of RNA viruses, the sole genus in the '' Togaviridae'' family. Alphaviruses belong to group IV of the Baltimore classification of viruses, with a positive-sense, single-stranded RNA genome. There are 32 alphaviruses, ...

''. Some Reoviruses are transmitted from arthropod vectors. All are RNA viruses. * One family of enveloped viruses causes

gastroenteritis Gastroenteritis, also known as infectious diarrhea and gastro, is an inflammation of the gastrointestinal tract including the stomach and intestine. Symptoms may include diarrhea, vomiting, and abdominal pain. Fever, lack of energy, and dehydrat ...

(''Coronaviridae''). All other viruses associated with gastroenteritis are non-enveloped.

Baltimore Group

This group of analysts defined multiple categories of virus. Groups: * I - dsDNA * II - ssDNA * III -

dsRNA Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carb ...

* IV - positive-sense ssRNA * V - negative-sense ssRNA * VI - ssRNA-RT * VII - dsDNA-RT

Clinical characteristics

The clinical characteristics of viruses may differ substantially among species within the same family:

References

External links

{{DEFAULTSORT:Virus Disease Pathogenic microbes

Structural Characteristics

Pragmatic Rules

Baltimore Group

Clinical characteristics

See also

References

External links