Discovery history and taxonomy
The first member of the family was discovered in 1997 by a group of researchers led by Nishizawa. The virus was isolated from the blood serum of a patient with the initials T.T. The clinical context of the discovery was quite alarming: the patient had post-transfusion hepatitis of unknown etiology, which initially led scientists to suspect a new infectious agent as the cause of the disease.
According to modern classification, the family Anelloviridae includes 9 genera. The name of the taxon comes from the Latin word anellus, which translates to "ring" and directly points to the specific structure of the viral genome.
The type species of the family is TTV (Torque Teno virus, which translates to "thin necklace virus"), which belongs to the genus Alphatorquevirus. In addition to classical TTV, other variants differing in their characteristics are distinguished within the family, such as mini-TTV (Torque Teno mini virus) and midi-TTV (Torque Teno midi virus).
Virion morphology and genome structure
Anelloviruses are classified as simple viruses—they are non-enveloped, meaning they lack an additional lipid supercapsid. Virion sizes are extremely small, with a diameter of only 30–32 nm.
Main structural characteristics:
- Capsid: has an icosahedral type of symmetry and consists of a structural protein designated as VP1.
- Genome: represented by circular single-stranded negative-sense DNA.
- Genetic diversity: the family is characterized by high variability—today, researchers distinguish more than 20 different genotypes of anelloviruses.
Reproduction features
The life cycle of anelloviruses is closely linked to host cells, but many details of their reproduction are still under study.
- Localization: it is hypothesized that viral DNA replication occurs in the nuclei of hematopoietic (blood-forming) cells.
- Virion assembly: the final formation process of new viral particles takes place in the cytoplasm of the infected cell.
- Cell exit: assembled virions leave the host cell by lysis (destruction).
- Reservoir: the main reservoir for maintaining the virus in the human body is presumably hepatocytes (liver cells).
Epidemiology and distribution
Despite the history of its discovery associated with hepatitis, the epidemiological profile of anelloviruses today looks completely different. They are found in 90% of the healthy population of the planet. In modern microbiology, anelloviruses are viewed not as classical pathogens, but as normal members of human microflora—the so-called healthy virome.
Infection occurs via several routes:
- Blood-borne route — transmission of the pathogen through infected blood and its components.
- Sexual route — transmission through unprotected sexual contact.
It is worth noting that the circulation of anelloviruses is not limited to the human population: viruses with similar characteristics circulate widely in nature among monkeys as well.
Briefly: answers to topical questions
Which genera of viruses belong to the family Anelloviridae?
The family Anelloviridae includes 9 genera, but only one is detailed by name.
- TTV virus (Alphatorquevirus) is the type species of the family, also known as the "thin necklace" virus (Torque Teno virus).
Other genera are not mentioned in the provided materials, but additional variants of the virus are distinguished, such as mini-TTV (Torque Teno mini virus) and midi-TTV (Torque Teno midi virus).
What genotypes of the TTV virus exist?
Specific names of TTV genotypes are not provided, but its high variability and tendency to frequent DNA mutations are noted. Data on the number of existing genotypes vary depending on the source:
- The general description of the family indicates that there are more than 20 genotypes.
- In the context of "non-A, non-G" hepatitis, 16 genotypes and a number of subtypes have been identified.
- When describing poorly studied hepatotropic viruses, it is mentioned that 3 genotypes and 9 subtypes have been identified.
To remember the essence of the family, connect the Latin "anellus" (ring), the shape of the genome (circular DNA), and the translation of the name of the type virus TTV ("thin necklace"). A necklace is also a ring.
Class and exam questions
What does the abbreviation TTV stand for?
TTV stands for Torque Teno virus ("thin necklace virus"). This is the type species of the family, belonging to the genus Alphatorquevirus.
Are anelloviruses the causative agents of hepatitis?
Although TTV was first isolated from a patient with post-transfusion hepatitis, anelloviruses are currently found in 90% of healthy people and are considered part of the normal human virome, rather than obligate pathogens.
What are the structural features of the anellovirus genome?
The anellovirus genome is represented by circular single-stranded negative-sense DNA. The family is characterized by high diversity—more than 20 genetic variants are distinguished.
What else to study on this topic
- Capsid organization and VP1 protein structure
- Replication mechanisms of single-stranded circular negative-sense DNA
- Interaction of anelloviruses with hematopoietic cells and hepatocytes
- The role of anelloviruses in the formation and functioning of the normal human virome
- Genetic diversity: features of genotypes and mini-TTV and midi-TTV variants
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