Giant viruses

The history of the study of giant viruses began in 1992 in England . Studying the causes of pneumonia outbreak, scientists investigated water samples taken from the air-cooling system. Samples were incubated for some time with Acanthamoeba polyphaga amoebas culture to reveal pathogens similar to Legionella spp . That live inside amoebas. Indeed, the researchers were able to detect an unknown pathogen, which was visible in a light microscope and was Gram positively , and therefore was attributed to bacteria. However, the newly discovered bacterium could never be grown in a pure culture without amoebas. For more than ten years, attempts to classify a new bacterium have failed. The standard method for the determination of new types of bacteria and archaea is based on the reproduction using the polymerase chain reaction (PCR) of a section of the genome encoding 16S rRNA and its subsequent sequencing . However, it was not possible to obtain this part of the genome of an unknown bacterium, despite the use of various PCR protocols. In 2003, an unknown microorganism was studied using electron microscopy by a French research group, Didier Raoul . It turned out that this is not a bacterium, but a very large virus with an icosahedral capsid. Due to its similarity with microorganisms, the new virus is called "mimirus" (from the English. Mimicking microbes - "similar to microorganisms"). From the very discovery of viruses at the end of the 19th century, it was considered that viruses could not be viewed with a light microscope, therefore the discovery of mimivirus contradicted the established dogmas of virology . The mimivirus did not have the 16S rRNA genes simply because viruses do not have ribosomes ^[3] .

After the discovery of mimivirus, many research groups began to incubate amoeba cultures with various environmental samples, and after some time, in many cases, very large viruses were detected in the culture. Many improvements have been made to the original protocol, making it more and more efficient. Subsequently, scientists began to grow viruses not only in cultures of amoebas, but also in cultures of other protists . Some types of mimiviruses are currently known for about a hundred. Giant viruses have been detected even in a sample of the Siberian permafrost . In recent years, several giant viruses have been detected using metagenomics . In 2008, the first virofag ( Sputnik ) was discovered - a virus that can multiply in cells only in the presence of a host virus (usually a giant virus) and interferes with its successful reproduction. Currently, more than ten types of virofag are known ^[3] .

Under giant viruses are usually understood viruses with a genome longer than 200 thousand base pairs (p. O. ) and virions more than 0.2 μm in diameter . In addition, giant viruses have a number of common genetic and structural features. First, their genomes are always represented by double-stranded DNA and contain a significant proportion - from 31% in Cedratvirus to 84% in . Orphan genes are called genes that are no longer found in any living organisms (in English sources, they are called ORFans because of a pun: ORF (open reading frame) is an open reading frame , and ORFan sounds like orphan - orphan) . Secondly, their genomes contain introns and (portions of protein molecules that can cut themselves and splice the ends of the gap), as well as mobile genetic elements ( in mimiviruses and MITEs in Pandoravirus salinus ) ^[4] .

The main difference between giant viruses and other viruses is that their genomes encode molecules that are involved in translation : aminoacyl-tRNA synthetase , translation factors and tRNA . Only Pithovirus sibericum has such genes. Representatives of the genera Marseillevirus , Pithovirus , Faustovirus , Kauamoebovirus and Cedratvirus do not have genes encoding tRNA. Giant viruses bring together some features of the structure. For example, the mimivirus and Marseillevirus virions are equipped with special fibrils. For the release of genetic material into the cytoplasm of amoeba, giant viruses have pores located in the tops of the capsids or teguments. Those giant viruses whose virions are covered with a real capsid have a special motif in their major protein, known as a double . It is present only in the capsid proteins of viruses with a double-stranded genome and nowhere else in the living world. Such proteins form tile-like oligomers , ultimately gathering into a closed protein shell ^[5] . In Faustovirus with a double-layer capsid, the jelly-roll motif is found only in the upper layer proteins ^[4] .

The taxonomic position of giant viruses has not yet been fully defined, and many recently described species, genera, and even families of giant viruses have not yet received official recognition by the International Committee on Virus Taxonomy ( Eng. International Committee on virus taxonomy , ICTV). So far ICTV has recognized two families of giant viruses: and . In 2012, it was proposed to merge giant viruses and NCLDV into a new order - Megavirales . Megavirales want to include Mimiviridae , Marseilleviridae , , , , and poxviruses ^{[4] in the} .

Mimiviridae

The mimivirus virion, the first open member of the Mimiviridae family, consists of an icosahedral capsid of 500 nm in size and 75 nm long fibrils covering it. These fibrils have a unique structure for viruses and allow the virion to attach to the cells of bacteria , arthropods and fungi . A year after the mimivirus was described, its genome was sequenced . It turned out that the mimivirus genome is represented by a circular double-stranded DNA of 1.2 million bp in length, which presumably contains 979 genes. Some of them, such as the genes of translation proteins (aminoacyl-tRNA synthetases and translation factors), have never been found in viral genomes before. In general, the mimivirus genes can be divided into four groups:

• king genes;
• genes acquired by horizontal transfer ;
• duplicated genes ( paralogs );
• orphan genes ^{[3] [4]} .

The genes that are also present in the so-called nuclear-cytoplasmic large DNA-containing viruses (NCLDCV), viruses that were considered the largest before the opening of the mimivirus, are referred to as core genes. Sequences borrowed from bacteria, eukaryotes , archaea and other viruses are found in the mimevirus genome. However, the vast majority of mimivirus genes are orphans, for which there are no homologs in all databases . In the virion mimivirus, in addition to genomic DNA, contains some amount of mRNA ^{[3] [4]} .

Now, mimirus and viruses close to it are divided into the Mimiviridae family, divided into three lines: A, B, and C. may serve as megavirus chiliensis . Some representatives of Mimiviridae could not be attributed to any of the listed lines, such as, for example, (CroV), which affects the protist ^[3] .

Marseilleviridae

Six years after the discovery of the mimivirus, another giant virus that attacks amoebas was described. Like mimivirus, it was found in water from an air-cooling structure, but this time in Paris . A new virus called Marseillevirus . His virion is smaller than the mimivirus virion and has an icosahedral capsid of 250 nm . The genome of Marseillevirus is represented by circular double-stranded DNA, in which there are 457 genes that are significantly different from the mimivirus genes. Among them are two genes encoding histone-like proteins. However, among the genes of Marseillevirus, it is possible to distinguish all the same four main groups - core genes, paralogs genes, horizontally acquired genes, and orphan genes. Like the mimivirus, the genome of Marseillevirus contains genes derived from eukaryotes (including the host amoeba), bacteria, archaea, and viruses, including the giant ones. It is assumed that such a high degree of mosaicism of the genome is due to the intense exchange of genes with other organisms living in the cytoplasm of the amoeba host ^[4] .

In 2011–2014, four viruses related to Marseillevirus were found in water samples from different parts of the world. In addition, a related virus was found in Tunis in an insect , and another relative of Marseillevirus was found in the feces of a healthy person in Senegal , which was the first precedent to detect giant viruses in specimens of human origin. Marseillevirus and related viruses are isolated in the Marseilleviridae family ^[4] .

Pandoravirus

In 2013, two new giant viruses were described, named Pandoravirus salinus and . In fact, these organisms were known for a long time, but, as in the case of mimivirus, their viral nature was not established immediately. In error, as in the case of mimivirus, he introduced an unusual size: their virions reach about 1 micron in length and 0.5 micron in diameter. The size of their genome is 1.9 and 2.5 million bp. accordingly, which is currently an absolute record among viruses. The overwhelming majority of the Pandoravirus genes (84% for P. salinus ) are orphan genes. Pandoravirus has its own unique transposons , known as (from the English. Miniature inverted repeat transposable elements - “miniature mobile elements with inverted repeats”) ^[4] .

Until 2017, it was believed that viruses of the genus Pandoravirus are characterized by the complete absence of genes in their genome that are homologous to any of the genes encoding capsid proteins. For this reason, they do not have a capsid and any structure, even if remotely similar to it. Their virions are surrounded by a special cover (tegument) about 70 nm thick , and at its top there is a pore through which the contents of the virion enter the cytoplasm of the amoeba. In 2017, a gene was identified in Pandoravirus that can encode a capsid protein. In addition, other viral traits are fully inherent in Pandoravirus : like all viruses, they multiply in cells and leave them as virions, and their genomes lack genes that encode components of ribosomes and proteins associated with cell division ^[4] .

In 2015, described the third species of the genus Pandoravirus - Pandoravirus inopinatum . Its genome contains 2.24 million bp. and by 85 and 89% coincide with the genomes of P. salinus and P. dulcis, respectively. In 2018, the discovery of three more species of the genus was reported - Pandoravirus quercus , Pandoravirus neocaledonia , Pandoravirus macleodensis . It was also proposed to isolate the genus Pandoravirus into its own family Pandoraviridae ^[6] .

Pithovirus

In 2013, the virus was discovered, which to this day is considered the largest virus, Pithovirus sibericum . It was isolated from a sample of the Siberian permafrost aged over 30 thousand years by cultivating Acanthamoeba castellanii in amoeba cells. Externally, his virions are similar to Pandoravirus virions, but much larger - their length can reach 1.5 microns , which is currently an absolute record in the viral world. Like Pandoravirus , Pithovirus virions are surrounded by a 60 nm tegument withapical sometimes in the form of a regular hexagon . Pithovirus doesn’t have a typical capsid either, however, in the genome of this virus, there was a gene remotely similar to the gene encoding the capsid protein in members of the Iridoviridae family. In terms of gene composition, Pithovirus is closest to Marseilleviridae and Iridoviridae . More than one fifth of the Pithovirus genome is represented by regularly located copies of the same non-coding repeat ^[4] .

Since the first Pithovirus was isolated from a very ancient specimen, it was suggested that the Pithovirus were extinct long ago. However, in 2016, another Pithovirus was found - Pithovirus massiliensis - in a wastewater sample from the south of France . Surprisingly, despite the enormous size of the Pithovirus virions, their genomes are not so large: the size of the P. sibericum genome is about half of the mimivirus genome ^[4] .

Mollivirus

In 2014, another giant virus, Mollivirus sibericum , was identified from the same permafrost pattern as Pithovirus . Like Pithovirus , it breeds in amoebas Acanthamoeba castellanii . The spherical mollivirus virion reaches 500–600 nm in diameter and contains a 625 kb long genome. In addition to the viral genome, many amoeba proteins, including proteins, are packaged into virions. Genetically mollivirus, although very remotely, is closest to Pandoravirus ^[4] .

Faustovirus

In addition to amoebas of the genus , the amoeba Vermamoeba vermiformis is used as a cell to isolate giant viruses, the most typical of human feces and hospital water samples. With the help of this amoeba in 2015 another gigantic virus was isolated from wastewater - Faustovirus . Its capsid has the form of an icosahedron and consists of two protein layers, and not one, like most viruses. Subsequently, viruses of the genus Faustovirus were found in different parts of the world, but in all cases they were detected only in wastewater, so that they can serve as an indicator of water contamination by faeces. Among giant viruses and NCLDVs, the close relatives of Faustovirus are Asfarviridae , porcine pathogens , but the Faustovirus genome is three times larger than the Asfarviridae genomes. Faustovirus genomes reach 456-491 thousand n. and contain 457-519 genes. It is curious that the genes encoding the capsid proteins are scattered over a length of 17 thousand bp, so these genes can be subjected to intense splicing . Prior to this, in the viral world, splicing has been described only in adenoviruses and in the mimivirus capsid protein gene ^[4] .

Kaumoebavirus

Using V. vermiformis for cultivation, along with various samples from the outside world, allowed us to describe another group of giant viruses, known as Kaumoebavirus . Like Faustovirus , they are isolated from wastewater samples and have no close relatives among the known viruses. The most similar to Kaumoebavirus are the viruses of the genus Faustovirus and the family Asfaviridae . Capsid has an icosahedral form. The capsid protein genes are scattered over a section of 5 thousand bp in length. Kaumoebavirus genome size is closest to Marseillevirus ^[4] .

Cedratvirus

In 2016, in a sample of water from Algeria, with the help of amoeba A. castellanii , a new giant virus, Cedratvirus, was discovered . Of the currently known viruses, the Pithovirus is closest to it, although only one fifth of the Cedratvirus genes resemble the Pithovirus genes. Cedratvirus differs from other giant viruses by the presence of double-layer integument. In the early stages of infection, virions are covered with a 40 nm tegument, and in mature virions, its thickness is 55 nm . The contents of the virion enter the cytoplasm through the apical pore. The size of the Cedratvirus genome is close to that of the Pithovirus . Another member of the genus Cedratvirus is described in 2017. In the genomes of both, there are no non-coding repeats that are so abundantly represented in the Pithovirus genome ^[4] .

Pacmanvirus

Pacmanvirus was described in 2017 using the amoeba A. castellanii . These viruses got their name from the capsid shape, which is observed with a negative staining in an electron microscope : it is similar to the protagonist of the video game Pac-Man of the same name. Pacmanvirus multiplies very quickly, and already 8 hours after infection, lysis of amoebic cells occurs. Pacmanvirus is similar in size to Kaumoebavirus and Faustovirus in terms of virions and genomes, and the closest relatives of Pacmanvirus are Faustovirus , Asfaviridae and Kaumoebavirus ^[4] .

Tupanvirus

In February 2018, they announced the discovery of two closely related giant viruses, called Tupanvirus Soda Lake and Tupanvirus Deep Ocean, according to the origin of the water samples from which they were extracted. They can infect amoebas A. castellanii and V. vermiformis . Tupanvirus capsids correspond approximately in size to mimi -virus (about 450 nm ), but they also have a long cylindrical tail about 550 nm long attached to the base of the capsid. None of the currently known viruses have such large appendages of the capsid ^[7] .

The Tupanvirus genome is represented by a linear double-stranded DNA with a length of about 1.5 million bp. The genome contains 1200-1400 open reading frames, of which about 380 are orphan genes. Species of the genus Tupanvirus are absolute champions among viruses in terms of the number of broadcast components encoded. In fact, for a complete set they lack only the ribosomes. They have genes of about 20 aminoacyl-tRNA synthetases, 70 tRNA , and Tupanvirus Deep Ocean even has tRNA for the rare amino acid pyrrolysine , eight translation initiation factors , one factor elongation and single factor termination , as well as a number of auxiliary proteins involved in translation. The closest relatives of Tupanvirus are mimiviruses, and so close that the genus Tupanvirus is supposed to be included in the Mimiviridae family ^[7] .

Medusavirus

In 2019, it was announced the discovery of a new giant virus that infects amoeba A. castellanii from a hot spring in Japan . A new virus called Medusavirus . It has an icosahedral capsid with a diameter of 260 nm , carrying unusual appendages with spherical tips. The genome is represented by a double-stranded DNA molecule with a length of 381 kb, it encodes 461 putative proteins. Numerous acts of horizontal gene transfer in both directions took place between Medusavirus and the amoeba host. Thanks to them, genes encoding all five histones and eukaryotic DNA polymerase have appeared in the Medusavirus genome, and genes encoding capsid proteins are found in the genome of A. castellanii . Morphologically and phylogenetically, the Medusavirus is very far from the other giant viruses, so the discoverers proposed to isolate it into their own family of Medusaviridae ^[8] .

Most currently known giant viruses infect amoebas of the genus Acanthamoeba . However, it is unknown whether they have other owners. These amoebas feed on a wide variety of microorganisms : bacteria, yeast, and other fungi, viruses, and algae ; therefore, there is a lot of foreign DNA in their cytoplasm. Probably, the mosaicism of the genomes of giant viruses is due to intensive horizontal gene transfer from “cell neighbors”. Some giant viruses are described in another type of amoebas, V. vermiformis . A number of distant relatives of mimiviruses infect marine flagellates and unicellular algae. Attempts to use cells other than amoebas for cultivating giant viruses have not yet succeeded ^[4] .

However, there is some evidence that giant viruses can live not only in amoebas. For example, experiments have shown that mimiviruses can invade phagocytic cells ( monocytes and macrophages ) in humans and mice , and in mice even described mimirus infection affecting macrophages. It is also shown that mimic virus can multiply in human mononuclear peripheral blood cells , stimulating the release of and inhibiting the expression of genes stimulated by interferon in these cells. In addition, viruses of the genus Marseillevirus can penetrate immortalized human T-lymphocytes , and they were even able to be found in macrophages from lymph nodes ^[4] .

The life cycle of giant viruses lasts from 6 to 24 hours. As a rule, viruses in the cell through phagocytosis , however, viruses of the genus Marseillevirus can enter the cytoplasm by endocytosis . This giant viruses are significantly different from other viruses that penetrate into the cell after interacting with receptors on its surface. After the virion enters the cytoplasm, its inner membrane , which lies beneath the capsid, merges with the vesicle membrane, and the contents of the virion are poured into the cytoplasm. After this, the formation of viral factories begins - special zones of the cytoplasm, where viral DNA replicates and viral particles are assembled. Often, when infected with giant viruses, the morphology of the nucleus also changes. In the cells infected with Pandoravirus or Mollivirus , there is an invagination of the nuclear envelope , and in the case of Mollivirus, virus factories even enter the nucleus. In fact, the viral factory becomes the functional nucleus of a cell infected with a virus (virocell) ^[4] .

The assembly of virions in giant viruses occurs in different ways. In the case of mimiviruses, the formation of the inner membrane, capsid assembly, DNA packaging and fibril assembly occur sequentially and are accompanied by the movement of virions from the center of the viral factory to its edges. In Pandoravirus and Mollivirus, the build of the shell and the internal contents of the virion occur simultaneously. The release of giant virus virions is accompanied by lysis of the amoeba cell, and only Mollivirus virions leave the cell through exocytosis ^[4] .

Judging by the presence in the genomes of giant viruses of genes encoding transcription and translation proteins, in terms of replication, they are more or less independent of the host cell. However, Pandoravirus , Mollivirus, and one of the Marseilleviridae are devoid of proteins associated with transcription, so replication still requires the core of the amoeba. In the case of one representative of Marseilleviridae, transcription begins in a viral factory, but, apparently, by attracting the transcriptional apparatus of the host cell ^[4] .

Together with the discovery of a new member of the family of mimiviruses, Mamavirus , the first virusphage was discovered - a virus whose reproduction depends on the host virus. In the viral factories of the Mamvirus, small icosahedral virions were found that did not resemble the Mamavirus virions. The new virus has been called the "virophage Sputnik" ^[4] .

The genomes of the virophages are represented by circular DNA from 17 to 29 thousand bp in length. and contain 16-34 genes, some of which are homologous to the genes of giant viruses. After Sputnik, several more virofagi were described, multiplying with the participation of mimiviruses of all three lines (A, B and C). Virofag was described, which could parasitize only on mimic viruses of lines B and C; line A mimiviruses were resistant to it. This virus was called Zamilon . At the same time, sequences belonging to Zamilon were found in the line A mimivirus genome. The cluster formed by them was named MIMIVIRE (from the English mimivirus virophage resistant element ), and at first it was thought that its principle of operation was similar to the work of the bacterial systems CRISPR / Cas, which provided protection against bacteriophages . Nevertheless, recent studies suggest that MIMIVIRE has nothing to do with CRISPR / Cas. It is curious that copies of the genomes of the virofag are found in the genome of the marine alga ^[4] .

Giant viruses suffer not only from virofagov. In 2012, in the genome of one of the mimiviruses, mobile genetic elements were found, called transovirones. Transpovirons consist of seven thousand bp. and contain 6-8 protein-coding genes, and at their ends are long . All transovirones encode proteins containing a helicase domain of type I and a domain with zinc fingers of the type Cys2His2 (C2H2). Apparently, for reproduction, transovirones use both their own proteins and those of the host virus. Transpovirons are detected even in the genomes of the virophages inserted into the B. natans alga genome ^[9] . As already mentioned, mobile genetic elements (known as MITEs) are found in the genome of Pandoravirus salinus . Like transovirones, they have terminal inverted repeats, but do not encode any proteins ^[10] .

One of the most unusual features separating giant viruses from other viruses is the presence of genes, the products of which are involved in translation. Tupanvirus even has a complete set of proteins and RNA required for translation, except for the components of ribosomes. French microbiologist Didier Raoul (who first studied mimirus) suggested that giant viruses arose as a result of the evolutionary reduction of an ancient cell and represent the fourth domain of life, along with archaea, bacteria and eukaryotes. It is possible that at the time of the emergence of giant viruses on Earth, there were several independently arisen lines of cellular organisms, of which one survived to this day, and the giant viruses may be descendants of one of the extinct lines ^[11] .

However, in the strict sense of the word, giant viruses cannot be a domain, since the separation of cellular organisms into three domains was carried out by comparing rRNA genes that giant viruses do not have. Therefore, in 2013, Didier Raoul proposed to abandon the system of three domains and go to the system of four TRUC - an abbreviation of Things Resisting Uncompleted Classification (from English - “entities that are not amenable to incomplete classification”). Thus, the whole earthly life can be divided into four TRUC - eukaryotes, bacteria, archaea and giant viruses. At the same time, the remaining viruses remain outside the system of the living world. The isolation of giant viruses into a separate branch of life was skeptically met by an American biologist, Evgeny Kunin , who believes that the isolation of giant viruses is associated with phylogeny reconstruction errors, and a large number of genes common with cellular organisms are the result of horizontal transfer ^[11] .

It is worth emphasizing that giant viruses can be safely called microorganisms , since microorganisms, by definition, are organisms that can be distinguished in a light microscope, which fully applies to giant viruses ^[3] .

The fact that the viral factory of giant viruses, in fact, is the nucleus of an infected cell (virocell), suggests that the evolution of giant viruses and the evolution of eukaryotes may be closely related. In fact, the similarity between the viral factory and the cell nucleus is not superficial: both structures lie in the cytoplasm, and often viral factories surround themselves with the membranes of the endoplasmic reticulum , which serve as a source of membranes for virions. Many NCLDVs have viral factories near the center of microtubule organization , which is involved in nuclear fission. Using atomic force microscopy , it was shown that viral factories are also formed by the fusion of vesicles resulting from the invagination of the nuclear envelope. Finally, Mollivirus and partly Pandoravirus use the nucleus itself as a viral factory, and nuclear membranes as a source for internal virion membranes ^[12] .

It can be assumed that the cell nucleus originated from a viral factory of the ancient NCLDV, which multiplied in a proto-eukaryotic cell. After that, the viral genome merged with the genome of the proto-eukaryotic cell and lost its ability to form virions, forever becoming part of the eukaryotic genome ^[12] .

They also suggested another scenario, according to which giant viruses, on the contrary, evolved from the nucleus of an ancient eukaryotic cell. At first glance, it is difficult to imagine how the cell nucleus can become a virion. However, it can be assumed that the cell nucleus became a viral factory after the genes necessary for the formation of virions appeared in it. However, it is unclear how a whole chromosome could be packaged into a virion ^[12] .

According to the third hypothesis, the cell nucleus emerged as a protective structure as a result of the interaction of the proto-eukaryotic cell with the virus. The nucleus made it possible to secure the replication and transcription of the genome of the cell from the action of the virus, but during evolution, most viruses learned to overcome this barrier ^[12] .

Apparently, giant viruses are widespread in nature: they were found in samples of sea and fresh water, as well as in soil samples collected around the world. Their host amoebas are also very widespread and often live alongside humans. Some giant viruses, namely mimiviruses, have been isolated from various animals - oysters , leeches , monkeys and cows . Marseillevirus was isolated from dipterous insects, and a faustovirus was once found in the body of the bumfret ^[13] .

Giant viruses have been repeatedly found in biological materials taken from humans. They were detected in the feces and blood of healthy people, scrapings of the upper respiratory tract of patients with pneumonia and even in fluid for contact lenses used by patients with keratitis . In 2013, Marseillevirus discovered an eleven- old child suffering from in the blood and lymph nodes. Giant viruses are often identified in human-related metagenomic data. Thus, sequences probably belonging to mimi viruses are found in human feces and coprolites , saliva , and vaginal mucosa . Sequences related to the virophages are found in the gastrointestinal tract . Pandoravirus , Pithovirus and Faustovirus were detected in the blood plasma of patients suffering from various liver pathologies ^[13] .

As noted earlier, mimiviruses can invade human and mouse phagocytes. It was shown that within 30 hours after mimivirus hit the mouse macrophage, the amount of viral DNA in the cell increased significantly, and the extract from infected macrophages led to lysis of amoebas. They also found that mimirus can multiply in mononuclear cells of human peripheral blood and suppress the expression of interferon-stimulated genes in these cells. 21 days after infection with Marseillevirus, immortalized human T lymphocytes, they were able to identify not only viral DNA, but also whole virions. Thus, giant viruses can successfully multiply outside amoebas ^[13] .

As you know, mimivirus was discovered by chance while investigating the causes of pneumonia outbreak. Indeed, mimiviruses are found in the blood plasma of patients with pneumonia in significantly larger numbers than in healthy people. In patients infected with pneumonia already in the hospital, numerous antibodies against mimivirus were detected in the blood. At the same time, independent studies have shown that mimiviruses are present in hospitals in much larger quantities than in ordinary rooms. One case of a laboratory assistant who got pneumonia and who worked a lot with mimivirus with his bare hands was described. Antibodies to 23 proteins of mimivirus were found in his blood, of which 4 were unique to mimivirus. A similar case occurred in 1968 with a laboratory technician who did not comply with safety regulations when working with the Epstein-Barr virus , which eventually became ill with infectious mononucleosis . As it became known later, infectious mononucleosis is caused by the Epstein-Barr virus. In two patients who returned to France from a trip to Laos and suffered from asthenia , fever , myalgia and nausea , antibodies to the virophage Sputnik, which is known to parasitize mimic viruses, were detected in the blood ^[13] .

Thus, at the moment it is still early to unambiguously record giant viruses in the list of human pathogens, but it can definitely be said that they are involved in the pathogenesis of many human diseases ^[13] .

Comments

Sources

• Elizaveta Minina. Giants of the viral world. Article on Biomolecula.ru (Neopr.) (August 31, 2018). The appeal date is January 22, 2019.