Liao ning virus, a new Chinese seadornavirus that replicates in transformed and embryonic mammalian cells

Isolation and Genomic Characterization of Kadipiro Virus from Mosquitoes in Yunnan, China

Background: Kadipiro virus (KDV) is a species of the new 12 segmented RNA virus grouped under the genus Seadornavirus within the Reoviridae family. It has previously been isolated or detected from mosquito, Odonata, and bat feces in Indonesia, China, and Denmark, respectively. Here, we describe the isolation and characterization of a viral strain from mosquitoes in Yunnan Province, China. Methods: Mosquitoes were collected overnight using light traps in Shizong county, on July 17, 2023. Virus was isolated from the mosquito homogenate and grown using baby hamster kidney and Aedes albopictus (C6/36) cells. Preliminary identification of the virus was performed by agarose gel electrophoresis (AGE). The full-genome sequences of the strain were determined by full-length amplification of cDNAs and sequenced using next-generation sequencing. Results: We isolated a viral strain (SZ_M48) from mosquitoes (Culex tritaeniorhynchus Giles) that caused cytopathogenic effects in C6/36 cells. AGE analysis indicated a genome consisting of 12 segments of double-stranded RNA that demonstrated a "6-5-1" pattern, similar to the migrating bands of KDV. Phylogenetic analysis based on the full-genome sequence revealed that SZ_M48 is more clustered with KDV isolates from Hubei and Shangdong in China than with Indonesian and Danish strains. The identity between SZ_M48 and SDKL1625 (Shandong, China) is slightly lower than that of QTM27331 (Hubei, China), and the identity with JKT-7075 (Indonesia) and 21164-6/M.dau/DK (Denmark) is the lowest. Conclusion: The full-genome sequence of the new KDV strain described in this study may be useful for surveillance of the evolutionary characteristics of KDVs. Moreover, these findings extend the knowledge about the genomic diversity, potential vectors, and the distribution of KDVs in China.

The Viromes of Mosquitoes from the Natural Landscapes of Western Siberia

The metagenomic analysis of mosquitoes allows for the genetic characterization of mosquito-associated viruses in different regions of the world. This study applied a metagenomic approach to identify novel viral sequences in seven species of mosquitoes collected from the Novosibirsk region of western Siberia. Using NGS sequencing, we identified 15 coding-complete viral polyproteins (genomes) and 15 viral-like partial sequences in mosquitoes. The complete sequences for novel viruses or the partial sequences of capsid proteins, hypothetical viral proteins, and RdRps were used to identify their taxonomy. The novel viral sequences were classified within the orders Tymovirales and Picornavirales and the families Partitiviridae, Totiviridae, Tombusviridae, Iflaviridae, Nodaviridae, Permutotetraviridae, and Solemoviridae, with several attributed to four unclassified RNA viruses. Interestingly, the novel putative viruses and viral sequences were mainly associated with the mosquito Coquillettidia richardii. This study aimed to increase our understanding of the viral diversity in mosquitoes found in the natural habitats of Siberia, which is characterized by very long, snowy, and cold winters.

The identification and genetic characteristics of Quang Binh virus from field-captured Culex tritaeniorhynchus (Diptera: Culicidae) from Guizhou Province, China

BACKGROUND

Mosquitoes carry a variety of viruses that can cause disease in humans, animals and livestock. Surveys for viruses carried by wild mosquitoes can significantly contribute to surveillance efforts and early detection systems. In addition to mosquito-borne viruses, mosquitoes harbor many insect-specific viruses (ISVs). Quang Binh virus (QBV) is one such example, categorized as an ISV within the Flavivirus genus (family Flaviviridae). QBV has been specifically documented in Vietnam and China, with reports limited to several mosquito species.

METHODS

The homogenate obtained from female mosquitoes was cultured on C6/36 (Aedes albopictus) and BHK-21 (baby hamster kidney) cell lines. Positive cultures were identified by reverse transcription-polymerase chain reaction (RT‒PCR) with taxon- or species-specific primers. Next-generation sequencing was employed to sequence the complete genomes of the identified positive samples. Subsequently, phylogenetic, gene homology, molecular evolutionary and genetic variation analyses were conducted.

RESULT

In 2021, a total of 32,177 adult female mosquitoes were collected from 15 counties in Guizhou Province, China. The predominant mosquito species identified were Culex tritaeniorhynchus, Armigeres subalbatus and Anopheles sinensis. Among the collected mosquitoes, three positive cultures were obtained from Cx. tritaeniorhynchus pools, revealing the presence of Quang Binh virus (QBV) RNA sequences. Phylogenetic analysis indicated that the three Guizhou isolates, along with the prototype isolate from Vietnam, formed distinct branches. These branches were primarily closely related to other QBV isolates reported in China. Comparative analysis revealed a high degree of nucleotide and amino acid homology between the Guizhou isolates and both Vietnamese and other indigenous Chinese isolates. Additionally, nonsynonymous single-nucleotide variants (SNVs) were observed in these strains compared to the QBV prototype strain.

CONCLUSION

This study represents the first report of QBV presences in Cx. tritaeniorhynchus mosquitoes in Guizhou Province, China. Phylogenetic tree analysis showed that the three Guizhou isolates were most closely related to the QBV genes found in China. In addition, the study of the genetic characteristics and variation of this virus provided a deeper understanding of QBV and enriched the baseline data of these insect-specific flaviviruses (ISFVs).

Full Genome Sequencing of Three Sedoreoviridae Viruses Isolated from Culicoides spp. (Diptera, Ceratopogonidae) in China

Sedoreoviridae is a family of viruses belonging to the order Reovirales and comprises six genera, two of which, Orbivirus and Seadornavirus, contain arboviruses that cause disease in humans and livestock. Areas such as Yunnan Province in southwestern China, have high arboviral activity due in part to warm and wet summers, which support high populations of biting flies such as mosquitoes and Culicoides. Three viral isolates previously obtained from Culicoides collected at cattle farms in Shizong County of Yunnan Province, China, between 2019 and 2020 were completely sequenced and identified as Banna virus (BAV) genotype A of Seadornavirus and serotypes 1 and 7 of epizootic hemorrhagic disease virus (EHDV) of Orbivirus. These results suggest that Culicoidestainanus and C. orientalis are potential vectors of BAV and EHDV, respectively, and represent the first association of a BAV with C. tainanus and of an arbovirus with C. orientalis. Analysis using VP9 generally agreed with the current groupings within this genus based on VP12, although the classification for some strains should be corrected. Furthermore, the placement of Kadipiro virus (KDV) and Liao ning virus (LNV) in Seadornavirus may need confirmation as phylogenetic analysis placed these viruses as sister to other species in the genus.

How relevant are in vitro culture models for study of tick-pathogen interactions?

Although tick-borne infectious diseases threaten human and animal health worldwide, with constantly increasing incidence, little knowledge is available regarding vector-pathogen interactions and pathogen transmission. In vivo laboratory study of these subjects using live, intact ticks is expensive, labor-intensive, and challenging from the points of view of biosafety and ethics. Several in vitro models have been developed, including over 70 continuous cell lines derived from multiple tick species and a variety of tick organ culture systems, facilitating many research activities. However, some limitations have to be considered in the translation of the results from the in vitro environment to the in vivo situation of live, intact ticks, and vertebrate hosts. In this review, we describe the available in vitro models and selected results from their application to the study of tick-borne viruses, bacteria, and protozoa, where possible comparing these results to studies in live, intact ticks. Finally, we highlight the strengths and weaknesses of in vitro tick culture models and their essential role in tick-borne pathogen research.

Zoonotic and reverse zoonotic transmission of viruses between humans and pigs

Humans and pigs share a close contact relationship, similar biological traits, and one of the highest estimated number of viruses compared to other mammalian species. The contribution and directionality of viral exchange between humans and pigs remain unclear for some of these viruses, but their transmission routes are important to characterize in order to prevent outbreaks of disease in both host species. This review collects and assesses the evidence to determine the likely transmission route of 27 viruses between humans and pigs.

Full-Genome Sequences of Alphacoronaviruses and Astroviruses from Myotis and Pipistrelle Bats in Denmark

Bat species worldwide are receiving increased attention for the discovery of emerging viruses, cross-species transmission, and zoonoses, as well as for characterizing virus infections specific to bats. In a previous study, we investigated the presence of coronaviruses in faecal samples from bats at different locations in Denmark, and made phylogenies based on short, partial ORF1b sequences. In this study, selected samples containing bat coronaviruses from three different bat species were analysed, using a non-targeted approach of next-generation sequencing. From the resulting metagenomics data, we assembled full-genome sequences of seven distinct alphacoronaviruses, three astroviruses, and a polyomavirus, as well as partial genome sequences of rotavirus H and caliciviruses, from the different bat species. Comparisons to published sequences indicate that the bat alphacoronaviruses belong to three different subgenera-i.e., Pedacovirus, Nyctacovirus, and Myotacovirus-that the astroviruses may be new species in the genus Mamastrovirus, and that the polyomavirus could also be a new species, but unassigned to a genus. Furthermore, several viruses of invertebrates-including two Rhopalosiphum padi (aphid) viruses and a Kadipiro virus-present in the faecal material were assembled. Interestingly, this is the first detection in Europe of a Kadipiro virus.

Near-Complete Sequence of a Highly Divergent Reovirus Genome Recovered from Callinectes sapidus

This report describes the sequence of a reovirus genome, discovered in Callinectes sapidus in Brazil. The genome sequence of Callinectes sapidus reovirus 2 (CsRV2) consists of 12 segments that encode 13 putative proteins. The predicted RNA-dependent RNA polymerase is highly similar to that of Eriocheir sinensis reovirus 905, suggesting that CsRV2 also belongs to the genus Cardoreovirus.

Strategies for Assessing Arbovirus Genetic Variability in Vectors and/or Mammals

Animal arboviruses replicate in their invertebrate vectors and vertebrate hosts. They use several strategies to ensure replication/transmission. Their high mutation rates and propensity to generate recombinants and/or genome segment reassortments help them adapt to new hosts/emerge in new geographical areas. Studying arbovirus genetic variability has been used to identify indicators which predict their potential to adapt to new hosts and/or emergence and in particular quasi-species. Multiple studies conducted with insect-borne viruses laid the foundations for the "trade-off" hypothesis (alternation of host transmission cycle constrains arbovirus evolution). It was extrapolated to tick-borne viruses, where too few studies have been conducted, even though humans faced emergence of numerous tick-borne virus during the last decades. There is a paucity of information regarding genetic variability of these viruses. In addition, insects and ticks do not have similar lifecycles/lifestyles. Indeed, tick-borne viruses are longer associated with their vectors due to tick lifespan. The objectives of this review are: (i) to describe the state of the art for all strategies developed to study genetic variability of insect-borne viruses both in vitro and in vivo and potential applications to tick-borne viruses; and (ii) to highlight the specificities of arboviruses and vectors as a complex and diverse system.

Origin and evolution of emerging Liao ning Virus (genus Seadornavirus, family Reoviridae)

Background

Liao ning virus (LNV) is a member of the genus Seadornavirus, family Reoviridae and has been isolated from kinds of vectors in Asia and Australia. However, there are no systematic studies describe the molecular genetic evolution and migration of LNVs. With the development of bioinformatics, viral genetic data combining the information of virus isolation time and locations could be integrated to infer the virus evolution and spread in nature.

Methods

Here, a phylogenetic and phylogeographic analysis using Bayesian Markov chain Monte Carlo simulations was conducted on the LNVs isolated from a variety of vectors during 1990–2014 to identify the evolution and migration patterns of LNVs.

Results

The results demonstrated that the LNV could be divided into 3 genotypes, of which genotype 1 mainly composed of LNVs isolated from Australia during 1990 to 2014 and the original LNV strain (LNV-NE97–31) isolated from Liaoning province in northern China in 1997, genotype 2 comprised of the isolates all from Xinjiang province in western China and genotype 3 consisted the isolates from Qinghai and Shanxi province of central China. LNVs emerged about 272 years ago and gradually evolved into three lineages in the order genotype 1, genotype 2 and genotype 3. Following phylogeographic analysis, it shows genotype 1 LNVs transmitted from Australia (113°E-153°E,10°S-42°S) to Liaoning province (118°E-125°E,38°N-43°N) in Northeast Asian continent then further spread across the central part of China to western China (75°E-95°E,35°N-50°N).

Conclusion

LNVs were initially isolated from Liaoning province of China in the Northeast Asia, however, the present study revealed that LNVs were first appeared in Australia in the South Pacific region and transmitted to mainland China then rapidly spread across China and evolved three different genotypes. The above results suggested that LNV had the characteristics of long-distance transmission and there were great genetic diversity existed in the LNV population. Notably, current information of 80 strains of LNVs are limited. It is of great importance to strengthen the surveillance of LNVs to explore its real origin in nature and monitoring of the LNVs’ population variation and maintain vigilance to avoid LNV breaking through the species barrier and further clarify its relationship to human and animal infection.

A viral metagenomic analysis reveals rich viral abundance and diversity in mosquitoes from pig farms

Mosquitoes harbour a diversity of viruses and are responsible for several mosquito-borne viral diseases of humans and animals, thereby leading to major public health concerns, and significant economic losses across the globe. Viral metagenomics offers a great opportunity for bulk analysis of viral genomes retrieved directly from environmental samples. In this study, we performed a viral metagenomic analysis of five pools of mosquitoes belonging to Aedes, Anopheles and Culex species, collected from different pig farms in the vicinity of Shanghai, China, to explore the viral community carried by mosquitoes. The resulting metagenomic data revealed that viral community in the mosquitoes was highly diverse and varied in abundance among pig farms, which comprised of more than 48 viral taxonomic families, specific to vertebrates, invertebrates, plants, fungi, bacteria and protozoa. In addition, a considerable number of viral reads were related to viruses that are not classified by host. The read sequences related to animal viruses included parvoviruses, anelloviruses, circoviruses, flavivirus, rhabdovirus and seadornaviruses, which might be taken up by mosquitoes from viremic animal hosts during blood feeding. Notably, sample G1 contained the most abundant sequence related to Banna virus, which is of public health interest because it causes encephalitis in humans. Furthermore, non-classified viruses also shared considerable virus sequences in all the samples, presumably belonging to unexplored virus category. Overall, the present study provides a comprehensive knowledge of diverse viral populations carried by mosquitoes at pig farms, which is a potential source of diseases for mammals including humans and animals. These viral metagenomic data are valuable for assessment of emerging and re-emerging viral epidemics.

First Isolation and Characterization of a Group C Banna Virus (BAV) from Anopheles sinensis Mosquitoes in Hubei, China

Banna virus (BAV) is considered to be an emerging human pathogen that is transmitted by blood-sucking insects. BAV was isolated from various species of mosquitoes, midges, and livestock. It is widely distributed geographically, since it was identified in China, Vietnam, and Indonesia. Previously reported evolution studies of BAV indicated that BAV can be divided into two groups, including isolates from China and Vietnam clustered in group A, and Indonesian isolates in group B. In this study, we report the isolation of a new strain of BAV named HB14-71-01 from Anopheles sinensis mosquitoes from Hubei, China. An in vitro comparison study of the HB14-71-01 isolate and the group A BAV revealed differences based on observed cytopathic effect, plaque size, and viral growth rates. Additionally, the phylogenetic analysis indicated that the Hubei isolate belongs to a novel genotype of BAV and emerged nearly 105 years ago (95% highest posterior density (HPD): 35–434), unlike the two previously reported genotypes A and B. Our findings extend the knowledge about the genomic diversity and potential vectors/hosts of BAVs and will improve understanding of the relationships between genetic variation and pathogenicity.

Identification and genetic analysis of Kadipiro virus isolated in Shandong province, China

Background

Kadipiro virus (KDV) belongs to the Reoviridae family, which consists of segmented, non-enveloped, double-stranded RNA viruses. It has previously been isolated from Culex, Anopheles, Armigeres and Aedes mosquitoes in Indonesia and China. Here, we describe the isolation and characterization of SDKL1625 from Anopheles sinensis mosquitoes in Shandong province, China.

Methods

In this study, we isolated Kadipiro virus in Aedes albopictus C6/36 cell culture and the complete genome sequencing was made by next generation sequencing.

Results

We isolated and characterized a Kadipiro virus from Anopheles sinensis mosquitoes in 2016 in Shandong province, China. Nucleotide and amino acid homology analysis of SDKL1625 showed higher levels of sequence identity with QTM27331 (Odonata, China, 2016) than with JKT-7075 (Culex fuscocephalus, Indonesia, 1981). The SDKL1625 has 86–97% amino acid identity with the JKT-7075, 88–99% amino acid identity with the QTM27331. Among the 12 fragments, VP1, VP2, VP4, VP6, VP7, VP9 and VP12 showed high amino acid identity (> 90%) and VP5 showed the lowest identity (86% and 88%).

Conclusions

This is the first identification of KDV from mosquito in China. Virus morphology and genome organization were also determined, which will further enrich our understanding of the molecular biological characteristics of KDV and seadornaviruses.

New genotypes of Liao ning virus (LNV) in Australia exhibit an insect-specific phenotype

Liao ning virus (LNV) was first isolated in 1996 from mosquitoes in China, and has been shown to replicate in selected mammalian cell lines and to cause lethal haemorrhagic disease in experimentally infected mice. The first detection of LNV in Australia was by deep sequencing of mosquito homogenates. We subsequently isolated LNV from mosquitoes of four genera (Culex, Anopheles, Mansonia and Aedes) in New South Wales, Northern Territory, Queensland and Western Australia; the earliest of these Australian isolates were obtained from mosquitoes collected in 1988, predating the first Chinese isolates. Genetic analysis revealed that the Australian LNV isolates formed two new genotypes: one including isolates from eastern and northern Australia, and the second comprising isolates from the south-western corner of the continent. In contrast to findings reported for the Chinese LNV isolates, the Australian LNV isolates did not replicate in vertebrate cells in vitro or in vivo, or produce signs of disease in wild-type or immunodeficient mice. A panel of human and animal sera collected from regions where the virus was found in high prevalence also showed no evidence of LNV-specific antibodies. Furthermore, high rates of virus detection in progeny reared from infected adult female mosquitoes, coupled with visualization of the virus within the ovarian follicles by immunohistochemistry, suggest that LNV is transmitted transovarially. Thus, despite relatively minor genomic differences between Chinese and Australian LNV strains, the latter display a characteristic insect-specific phenotype.

Mosquito-Associated Viruses in China

Mosquitoes are classified into approximately 3500 species and further grouped into 41 genera. Epidemiologically, they are considered to be among the most important disease vectors in the world and they can harbor a wide variety of viruses. Several mosquito viruses are considered to be of significant medical importance and can cause serious public health issues throughout the world. Such viruses are Japanese encephalitis virus (JEV), dengue virus (DENV), chikungunya virus (CHIKV), and Zika virus (ZIKV). Others are the newly recognized mosquito viruses such as Banna virus (BAV) and Yunnan orbivirus (YNOV) with unclear medical significance. The remaining mosquito viruses are those that naturally infect mosquitoes but do not appear to infect humans or other vertebrates. With the continuous development and improvement of mosquito and mosquito-associated virus surveillance systems in China, many novel mosquito-associated viruses have been discovered in recent years. This review aims to systematically outline the history, characteristics, distribution, and/or current epidemic status of mosquito-associated viruses in China.

Metagenomic Virome Analysis of Culex Mosquitoes from Kenya and China

Many blood-feeding arthropods are known vectors of viruses that are a source of unprecedented global health concern. Mosquitoes are an integral part of these arthropod vectors. Advancements in next-generation sequencing and bioinformatics has expanded our knowledge on the richness of viruses harbored by arthropods. In the present study, we applied a metagenomic approach to determine the intercontinental virome diversity of Culex quinquefasciatus and Culex tritaeniorhynchus in Kwale, Kenya and provinces of Hubei and Yunnan in China. Our results showed that viromes from the three locations were strikingly diverse and comprised 30 virus families specific to vertebrates, invertebrates, plants, and protozoa as well as unclassified group of viruses. Though sampled at different times, both Kwale and Hubei mosquito viromes were dominated by vertebrate viruses, in contrast to the Yunnan mosquito virome, which was dominated by insect-specific viruses. However, each virome was unique in terms of virus proportions partly influenced by type of ingested meals (blood, nectar, plant sap, environment substrates). The dominant vertebrate virus family in the Kwale virome was Papillomaviridae (57%) while in Hubei it was Herpesviridae (30%) and the Yunnan virome was dominated by an unclassified viruses group (27%). Given that insect-specific viruses occur naturally in their hosts, they should be the basis for defining the viromes. Hence, the dominant insect-specific viruses in Kwale, Hubei, and Yunnan were Baculoviridae, Nimaviridae and Iflaviridae, respectively. Our study is preliminary but contributes to growing and much needed knowledge, as mosquito viromes could be manipulated to prevent and control pathogenic arboviruses.

Arboviruses and their related infections in China: A comprehensive field and laboratory investigation over the last 3 decades

Since the 1980s, a comprehensive field and laboratory investigation has been conducted throughout China, and a total of 29 virus species belonging to 7 families and 13 genera were identified through virological, morphological, and immunological methods, as well as whole-genome sequencing and molecular genetic analyses. Most of the virus isolates belong to 9 genera in the families Flaviviridae, Bunyaviridae, Togaviridae, and Reoviridae. Among them, 4 genera (Orthobunyavirus, Bunyavirus, Phlebovirus, and Nairovirus) belong to the family Bunyaviridae and 3 genera (Seadonavirus, Orbivirus, and Cypovirus) belong to the family Reoviridae. Analyses of the relationships between viruses and human/animal diseases indicated that Japanese encephalitis virus, dengue virus, severe fever with thrombocytopenia syndrome virus, tick-borne encephalitis virus, Crimean-Congo hemorrhagic fever virus, West Nile virus, and Tahyna virus can cause human and animal infections and disease epidemics in China. This review systematically introduces the current status of the diversity and geographical distribution of arboviruses and vectors in China. In addition, our results provide strong technical support for the prevention and control of arboviral diseases, the treatment of epidemics, and the early warning and prediction of diseases, and so they are significant for the control and prevention of arboviral diseases in Asia and around the world.

High-Resolution Metatranscriptomics Reveals the Ecological Dynamics of Mosquito-Associated RNA Viruses in Western Australia

Mosquitoes harbor a high diversity of RNA viruses, including many that impact human health. Despite a growing effort to describe the extent and nature of the mosquito virome, little is known about how these viruses persist, spread, and interact with both their hosts and other microbes. To address this issue we performed a metatranscriptomics analysis of 12 Western Australian mosquito populations structured by species and geographic location. Our results identified the complete genomes of 24 species of RNA viruses from a diverse range of viral families and orders, among which 19 are newly described. Comparisons of viromes revealed a striking difference between the two mosquito genera, with viromes of mosquitoes of the Aedes genus exhibiting substantially less diversity and lower abundances than those of mosquitoes of the Culex genus, within which the viral abundance reached 16.87% of the total non-rRNA. In addition, there was little overlap in viral diversity between the two genera, although the viromes were very similar among the three Culex species studied, suggesting that the host taxon plays a major role in structuring virus diversity. In contrast, we found no evidence that geographic location played a major role in shaping RNA virus diversity, and several viruses discovered here exhibited high similarity (95 to 98% nucleotide identity) to those from Indonesia and China. Finally, using abundance-level and phylogenetic relationships, we were able to distinguish potential mosquito viruses from those present in coinfecting bacteria, fungi, and protists. In sum, our metatranscriptomics approach provides important insights into the ecology of mosquito RNA viruses.IMPORTANCE Studies of virus ecology have generally focused on individual viral species. However, recent advances in bulk RNA sequencing make it possible to utilize metatranscriptomic approaches to reveal both complete virus diversity and the relative abundance of these viruses. We used such a metatranscriptomic approach to determine key aspects of the ecology of mosquito viruses in Western Australia. Our results show that RNA viruses are some of the most important components of the mosquito transcriptome, and we identified 19 new virus species from a diverse set of virus families. A key result was that host genetic background plays a more important role in shaping virus diversity than sampling location, with Culex species harboring more viruses at higher abundance than those from Aedes mosquitoes.

Comparative genomics shows that viral integrations are abundant and express piRNAs in the arboviral vectors Aedes aegypti and Aedes albopictus

Background

Arthropod-borne viruses (arboviruses) transmitted by mosquito vectors cause many important emerging or resurging infectious diseases in humans including dengue, chikungunya and Zika. Understanding the co-evolutionary processes among viruses and vectors is essential for the development of novel transmission-blocking strategies. Episomal viral DNA fragments are produced from arboviral RNA upon infection of mosquito cells and adults. Additionally, sequences from insect-specific viruses and arboviruses have been found integrated into mosquito genomes.

Results

We used a bioinformatic approach to analyse the presence, abundance, distribution, and transcriptional activity of integrations from 425 non-retroviral viruses, including 133 arboviruses, across the presently available 22 mosquito genome sequences. Large differences in abundance and types of viral integrations were observed in mosquito species from the same region. Viral integrations are unexpectedly abundant in the arboviral vector species Aedes aegypti and Ae. albopictus, in which they are approximately ~10-fold more abundant than in other mosquito species analysed. Additionally, viral integrations are enriched in piRNA clusters of both the Ae. aegypti and Ae. albopictus genomes and, accordingly, they express piRNAs, but not siRNAs.

Conclusions

Differences in the number of viral integrations in the genomes of mosquito species from the same geographic area support the conclusion that integrations of viral sequences is not dependent on viral exposure, but that lineage-specific interactions exist. Viral integrations are abundant in Ae. aegypti and Ae. albopictus, and represent a thus far underappreciated component of their genomes. Additionally, the genome locations of viral integrations and their production of piRNAs indicate a functional link between viral integrations and the piRNA pathway. These results greatly expand the breadth and complexity of small RNA-mediated regulation and suggest a role for viral integrations in antiviral defense in these two mosquito species.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3903-3) contains supplementary material, which is available to authorized users.

Viral component of the human genome

Relationships between viruses and their human host are traditionally described from the point of view taking into consideration hosts as victims of viral aggression, which results in infectious diseases. However, these relations are in fact two-sided and involve modifications of both the virus and host genomes. Mutations that accumulate in the populations of viruses and hosts may provide them advantages such as the ability to overcome defense barriers of host cells or to create more efficient barriers to deal with the attack of the viral agent. One of the most common ways of reinforcing anti-viral barriers is the horizontal transfer of viral genes into the host genome. Within the host genome, these genes may be modified and extensively expressed to compete with viral copies and inhibit the synthesis of their products or modulate their functions in other ways. This review summarizes the available data on the horizontal gene transfer between viral and human genomes and discusses related problems.

Commensal Viruses of Mosquitoes: Host Restriction, Transmission, and Interaction with Arboviral Pathogens

Recent advances in virus detection strategies and deep sequencing technologies have enabled the identification of a multitude of new viruses that persistently infect mosquitoes but do not infect vertebrates. These are usually referred to as insect-specific viruses (ISVs). These novel viruses have generated considerable interest in their modes of transmission, persistence in mosquito populations, the mechanisms that restrict their host range to mosquitoes, and their interactions with pathogens transmissible by the same mosquito. In this article, we discuss studies in our laboratory and others that demonstrate that many ISVs are efficiently transmitted directly from the female mosquito to their progeny via infected eggs, and, moreover, that persistent infection of mosquito cell cultures or whole mosquitoes with ISVs can restrict subsequent infection, replication, and transmission of some mosquito-borne viral pathogens. This suggests that some ISVs may act as natural regulators of arboviral transmission. We also discuss viral and host factors that may be responsible for their host restriction.

The plasma virome of febrile adult Kenyans shows frequent parvovirus B19 infections and a novel arbovirus (Kadipiro virus)

Viral nucleic acids present in the plasma of 498 Kenyan adults with unexplained fever were characterized by metagenomics analysis of 51 sample pools. The highest to lowest fraction of plasma pools was positive for parvovirus B19 (75 %), pegivirus C (GBV-C) (67 %), alpha anellovirus (59 %), gamma anellovirus (55 %), beta anellovirus (41 %), dengue virus genotype 2 (DENV-2) (16 %), human immunodeficiency virus type 1 (6 %), human herpesvirus 6 (6 %), HBV (4 %), rotavirus (4 %), hepatitis B virus (4 %), rhinovirus C (2 %), Merkel cell polyomavirus (MCPyV; 2 %) and Kadipiro virus (2 %). Ranking by overall percentage of viral reads yielded similar results. Characterization of viral nucleic acids in the plasma of a febrile East African population showed a high frequency of parvovirus B19 and DENV infections and detected a reovirus (Kadipiro virus) previously reported only in Asian Culex mosquitoes, providing a baseline to compare with future virome studies to detect emerging viruses in this region.

Isolation and Genetic Characterization of Mangshi Virus: A Newly Discovered Seadornavirus of the Reoviridae Family Found in Yunnan Province, China

BACKGROUND

Seadornavirus is a genus of viruses in the family Reoviridae, which consists of Banna virus, Kadipiro virus, and Liao ning virus. Banna virus is considered a potential pathogen for zoonotic diseases. Here, we describe a newly discovered Seadornavirus isolated from mosquitos (Culex tritaeniorhynchus) in Yunnan Province, China, which is related to Banna virus, and referred to as Mangshi virus.

METHODS AND RESULTS

The Mangshi virus was isolated by cell culture in Aedes albopictus C6/36 cells, in which it replicated and caused cytopathic effects, but not in mammalian BHK-21 or Vero cells. Polyacrylamide gel analysis revealed a genome consisting of 12 segments of double-stranded RNA, with a "6-4-2" pattern in which the migrating bands were different from those of the Banna virus. Complete genome sequencing was performed by full-length amplification of cDNAs. Sequence analysis showed that seven highly conserved nucleotides and three highly conserved nucleotides were present at the ends of the 5'- and 3'-UTRs in each of 12 genome segments. The amino acid identities of Mangshi virus shared with Balaton virus varied from 27.3% (VP11) to 72.3% (VP1) with Banna virus varying from 18.0% (VP11) to 63.9% (VP1). Phylogenetic analysis based on amino acid sequences demonstrated that Mangshi virus is a member of the genus Seadornavirus and is most closely related to, but distinct from, Balaton virus and Banna virus in the genus Seadornavirus of the family Reoviridae.

CONCLUSION

Mangshi virus isolated from mosquitoes (C. tritaeniorhynchus) was identified as a newly discovered virus in the genus Seadornavirus and is phylogenetically close to Banna virus, suggesting that there is genetic diversity of seadornaviruses in tropical and subtropical areas of Southeast Asia.

Isolation of Tibet orbivirus, TIBOV, from Culicoides Collected in Yunnan, China

We isolated a novel virus strain (YN12246) from Culicoides spp. specimens collected at the China-Laos-Myanmar border in southern Yunnan Province. This virus had a cytopathic effect (CPE) on both insect cells (C6/36) and mammalian cells (BHK-21). Electron microscopy revealed the structure of the virions to be spherical with a diameter of 75 nm. Polyacrylamide gel analysis demonstrated that the viral genome consisted of 10 segments of double-stranded RNA (dsRNA), with a distribution pattern of 3-3-3-1. The coding sequences of 9 genome segments of YN12246 (Seg1, Seg3-Seg10) were obtained by high-throughput sequencing and Sanger sequencing. Comparisons of conserved genome segments 1 and 3 (Seg1 and Seg3), encoding the polymerase-VP1 and sub-core T2 protein, respectively, showed that YN12246 groups with the Culicoides-borne orbiviruses. The highest levels of sequence identity were detected between YN12246 and Tibet orbivirus (TIBOV), indicating that they belong to the same virus species (with amino acid identity of 98.8% and 96.4% for the polymerase and T2 protein, respectively). The data presented here confirm that YN12246 is a member of the TIBOV species, which was first isolated from mosquitoes in 2009. This is the first report of the isolation of TIBOV from Culicoides.

Immunisation with bacterial expressed VP2 and VP5 of bluetongue virus (BTV) protect α/β interferon-receptor knock-out (IFNAR(-/-)) mice from homologous lethal challenge

BTV-4 structural proteins VP2 (as two domains: VP2D1 and VP2D2), VP5 (lacking the first 100 amino acids: VP5Δ1-100) and full-length VP7, expressed in bacteria as soluble glutathione S-transferase (GST) fusion-proteins, were used to immunise Balb/c and α/β interferon receptor knock-out (IFNAR(-/-)) mice. Neutralising antibody (NAbs) titres (expressed as log10 of the reciprocal of the last dilution of mouse serum which reduced plaque number by ≥50%) induced by the VP2 domains ranged from 1.806 to 2.408 in Balb/c and IFNAR(-/-) mice. The immunised IFNAR(-/-) mice challenged with a homologous live BTV-4 survived and failed to develop signs of infection (ocular discharge and apathy). Although subsequent attempts to isolate virus were unsuccessful (possibly reflecting presence of neutralising antibodies), a transient/low level viraemia was detected by real time RT-PCR. In contrast, mice immunised with the two VP2 domains with or without VP5Δ1-100 and VP7, then challenged with the heterologous serotype, BTV-8, all died by day 7 post-infection. We conclude that immunisation with bacterially-expressed VP2 domains can induce strong serotype-specific NAb responses. Bacterial expression could represent a cost effective and risk-free alternative to the use of live or inactivated vaccines, particularly if viruses prove to be difficult to propagate in cell culture (like BTV-25). A vaccine based on bacterially expressed VP2 and VP5 of BTV is also DIVA-compatible.

Enhanced arbovirus surveillance with deep sequencing: Identification of novel rhabdoviruses and bunyaviruses in Australian mosquitoes

Viral metagenomics characterizes known and identifies unknown viruses based on sequence similarities to any previously sequenced viral genomes. A metagenomics approach was used to identify virus sequences in Australian mosquitoes causing cytopathic effects in inoculated mammalian cell cultures. Sequence comparisons revealed strains of Liao Ning virus (Reovirus, Seadornavirus), previously detected only in China, livestock-infecting Stretch Lagoon virus (Reovirus, Orbivirus), two novel dimarhabdoviruses, named Beaumont and North Creek viruses, and two novel orthobunyaviruses, named Murrumbidgee and Salt Ash viruses. The novel virus proteomes diverged by ≥ 50% relative to their closest previously genetically characterized viral relatives. Deep sequencing also generated genomes of Warrego and Wallal viruses, orbiviruses linked to kangaroo blindness, whose genomes had not been fully characterized. This study highlights viral metagenomics in concert with traditional arbovirus surveillance to characterize known and new arboviruses in field-collected mosquitoes. Follow-up epidemiological studies are required to determine whether the novel viruses infect humans.

Endogenous tick viruses and modulation of tick-borne pathogen growth

Ticks transmit a wide range of viral, bacterial and protozoan pathogens, many of which can establish persistent infections of lifelong duration in the vector tick and in some cases are transmitted transovarially to the next generation. In addition many ixodid and argasid tick cell lines and, by inference the parent ticks from which they were derived, harbor endogenous viruses (ETV) of which almost nothing is known. In general, low level persistent infections with viral pathogens (arboviruses) are not known to have a deleterious effect on tick survival and fitness, suggesting that they can strike a balance with the tick innate immune response. This tolerance of arbovirus infection may be modulated by the permanent presence of ETV in the host cell. In mosquito cells, temporary or permanent silencing of the genes of an endogenous virus by RNA interference can result in changes in replication rate of a co-infecting arbovirus. We propose that tick cell lines offer a useful model system for in vitro investigation of the modulatory effect of ETV on superinfecting pathogen survival and replication in ticks, using the molecular manipulation techniques applied to insect cells.

Identification and genomic characterization of a novel fish reovirus, Hubei grass carp disease reovirus, isolated in 2009 in China

A novel fish reovirus, Hubei grass carp disease reovirus (HGDRV; formerly grass carp reovirus strain 104, GCRV104), was isolated from diseased grass carp in China in 2009 and the full genome sequence was determined. This reovirus was propagated in a grass carp kidney cell line with a typical cytopathic effect. The total size of the genome was 23 706 bp with a 51 mol% G+C content, and the 11 dsRNA segments encoded 12 proteins (two proteins encoded by segment 11). A nucleotide sequence similarity search using blastn found no significant matches except for segment 2, which partially matched that of the RNA-dependent RNA polymerase (RdRp) from several viruses in the genera Aquareovirus and Orthoreovirus of the family Reoviridae. At the amino acid level, seven segments (Seg-1 to Seg-6, and Seg-8) matched with species in the genera Aquareovirus (15-46 % identities) and Orthoreovirus (12-44 % identities), while for four segments (Seg-7, Seg-9, Seg-10 and Seg-11) no similarities in these genera were found. Conserved terminal sequences, 5'-GAAUU----UCAUC-3', were found in each HGDRV segment at the 5' and 3' ends, and the 5'-terminal nucleotides were different from any known species in the genus Aquareovirus. Phylogenetic analysis based on RdRp amino acid sequences from members of the family Reoviridae showed that HGDRV clustered with aquareoviruses prior to joining a branch common with orthoreoviruses. Based on these observations, we propose that HGDRV is a new species in the genus Aquareovirus that is distantly related to any known species within this genus.

Novel seadornavirus (family Reoviridae) related to Banna virus in Europe

Banna virus, whose genome is composed of 12 segments of double-stranded RNA, is a member of the genus Seadornavirus in the family Reoviridae and is thought to be an emerging mosquito-transmitted human pathogen in Southeast Asia. A novel phylogenetic relative of Banna virus (Balaton virus, BALV, JX947843-JX947850 and KC522611-KC522612) was identified using viral metagenomics in the intestinal contents of freshwater carp (Cyprinus carpio) in Hungary. The amino acid sequence identity of Balaton virus to homologous proteins of Banna viruses was 25-26 % for segment 12 (VP12) and 61-62 % for segment 1 (VP1), indicating that Balaton virus potentially represents a novel seadornavirus species. This study demonstrates that seadornaviruses are genetically diverse, not restricted geographically to Southeast Asia and present in an aquatic environment.

Isolates of Liao ning virus from wild-caught mosquitoes in the Xinjiang province of China in 2005

Liao ning virus (LNV) is related to Banna virus, a known human-pathogen present in south-east Asia. Both viruses belong to the genus Seadornavirus, family Reoviridae. LNV causes lethal haemorrhage in experimentally infected mice. Twenty seven isolates of LNV were made from mosquitoes collected in different locations within the Xinjiang province of north-western China during 2005. These mosquitoes were caught in the accommodation of human patients with febrile manifestations, or in animal barns where sheep represent the main livestock species. The regions where LNV was isolated are affected by seasonal encephalitis, but are free of Japanese encephalitis (JE). Genome segment 10 (Seg-10) (encoding cell-attachment and serotype-determining protein VP10) and Seg-12 (encoding non-structural protein VP12) were sequenced for multiple LNV isolates. Phylogenetic analyses showed a less homogenous Seg-10 gene pool, as compared to segment 12. However, all of these isolates appear to belong to LNV type-1. These data suggest a relatively recent introduction of LNV into Xinjiang province, with substitution rates for LNV Seg-10 and Seg-12, respectively, of 2.29×10⁻⁴ and 1.57×10⁻⁴ substitutions/nt/year. These substitution rates are similar to those estimated for other dsRNA viruses. Our data indicate that the history of LNV is characterized by a lack of demographic fluctuations. However, a decline in the LNV population in the late 1980s - early 1990s, was indicated by data for both Seg-10 and Seg-12. Data also suggest a beginning of an expansion in the late 1990s as inferred from Seg-12 skyline plot.

Evaluation of the human host range of bovine and porcine viruses that may contaminate bovine serum and porcine trypsin used in the manufacture of biological products

Current U.S. requirements for testing cell substrates used in production of human biological products for contamination with bovine and porcine viruses are U.S. Department of Agriculture (USDA) 9CFR tests for bovine serum or porcine trypsin. 9CFR requires testing of bovine serum for seven specific viruses in six families (immunofluorescence) and at least 2 additional families non-specifically (cytopathicity and hemadsorption). 9CFR testing of porcine trypsin is for porcine parvovirus. Recent contaminations suggest these tests may not be sufficient. Assay sensitivity was not the issue for these contaminations that were caused by viruses/virus families not represented in the 9CFR screen. A detailed literature search was undertaken to determine which viruses that infect cattle or swine or bovine or porcine cells in culture also have human host range [ability to infect humans or human cells in culture] and to predict their detection by the currently used 9CFR procedures. There are more viruses of potential risk to biological products manufactured using bovine or porcine raw materials than are likely to be detected by 9CFR testing procedures; even within families, not all members would necessarily be detected. Testing gaps and alternative methodologies should be evaluated to continue to ensure safe, high quality human biologicals.

Liao ning virus in China

BACKGROUND

Liao ning virus is in the genus Seadornavirus within the family Reoviridae and has a genome composed of 12 segments of double-stranded RNA (dsRNA). It is transmitted by mosquitoes and only isolated in China to date and it is the only species within the genus Seadornavirus which was reported to have been propagated in mammalian cell lines. In the study, we report 41 new isolates from northern and southern Xinjiang Uygur autonomous region in China and describe the phylogenetic relationships among all 46 Chinese LNV isolates.

FINDINGS

The phylogenetic analysis indicated that all the isolates evaluated in this study can be divided into 3 different groups that appear to be related to geographic origin based on partial nucleotide sequence of the 10th segment which is predicted to encode outer coat proteins of LNV. Bayesian coalescent analysis estimated the date of the most recent common ancestor for the current Chinese LNV isolates to be 318 (with a 95% confidence interval of 30-719) and the estimated evolutionary rates is 1.993 × 10-3 substitutions per site per year.

CONCLUSIONS

The results indicated that LNV may be an emerging virus at a stage that evaluated rapidly and has been widely distributed in the north part of China.

Nucleotide sequences of four RNA segments of a reovirus isolated from the mud crab Scylla serrata provide evidence that this virus belongs to a new genus in the family Reoviridae

This is the first sequence-based characterization of mud crab (Scylla serrata) reovirus (SsRV), which causes severe disease of cultured mud crabs in southern China. We sequenced and analyzed genome segments S1, S2, S3, and S7, which were 4,327, 2,721, 2,715, and 1,517 nucleotides long, respectively. Conserved motifs were found at the 5' (AUAAAU) and 3' (AACGAU) ends of each segment. RNA segments S1, S2, S3, and S7 each contained a single open reading frame (ORF) that encoded predicted proteins of 160, 100, 96, and 46 kDa, respectively. The ORFs of segments S1 and S2 showed distant homologies (< 25%) with cognate genes of other reoviruses, whereas the ORFs of segments S3 and S7 had no homologies with any other viral genes. Based on these observations, we propose that SsRV should be considered a member of a new genus in the family Reoviridae.

Endogenous viral elements in animal genomes

Integration into the nuclear genome of germ line cells can lead to vertical inheritance of retroviral genes as host alleles. For other viruses, germ line integration has only rarely been documented. Nonetheless, we identified endogenous viral elements (EVEs) derived from ten non-retroviral families by systematic in silico screening of animal genomes, including the first endogenous representatives of double-stranded RNA, reverse-transcribing DNA, and segmented RNA viruses, and the first endogenous DNA viruses in mammalian genomes. Phylogenetic and genomic analysis of EVEs across multiple host species revealed novel information about the origin and evolution of diverse virus groups. Furthermore, several of the elements identified here encode intact open reading frames or are expressed as mRNA. For one element in the primate lineage, we provide statistically robust evidence for exaptation. Our findings establish that genetic material derived from all known viral genome types and replication strategies can enter the animal germ line, greatly broadening the scope of paleovirological studies and indicating a more significant evolutionary role for gene flow from virus to animal genomes than has previously been recognized.

The presence of retrovirus sequences in animal genomes has been recognized since the 1970s, but is readily explained by the fact that these viruses integrate into chromosomal DNA as part of their normal replication cycle. Unexpectedly, however, we identified a large and diverse population of sequences in animal genomes that are derived from non-retroviral viruses. Analysis of these sequences—which represent all known virus genome types and replication strategies—reveals new information about the evolutionary history of viruses, in many cases providing the first and only direct evidence for their ancient origins. Additionally, we provide evidence that the functionality of one of these sequences has been maintained in the host genome over many millions of years, raising the possibility that captured viral sequences may have played a larger than expected role in host evolution.

Complete sequence of Great Island virus and comparison with the T2 and outer-capsid proteins of Kemerovo, Lipovnik and Tribec viruses (genus Orbivirus, family Reoviridae)

The complete nucleotide sequence of Great Island virus (GIV) genome was determined, along with genome segments (Seg) 1, 2 and 6 of Kemerovo (KEMV), Lipovnik (LIPV) and Tribec (TRBV) viruses. All four viruses, together with Broadhaven virus, are currently classified within the species Great Island virus and have been isolated from ticks, birds or humans. Sequence comparisons showed that Seg-4 of GIV encoded the outer-capsid protein responsible for cell attachment, although it was approximately half the length of its counterpart in the Culicoides or mosquito-transmitted orbiviruses. A second overlapping ORF (in the +2 reading frame) was identified in Seg-9 of GIV, encoding a putative dsRNA-binding protein. Phylogenetic analyses of the RNA-dependent RNA polymerase (Pol) and T2 protein amino acid sequences indicated that the tick-borne orbiviruses represent an ancestral group from which the mosquito-borne orbiviruses have evolved. This mirrors the evolutionary relationships between the arthropod vectors of these viruses, supporting a co-speciation hypothesis for these arboviruses and their arthropod-vectors. Phylogenetic analyses of the T2 proteins of KEMV, LIPV, TRBV and GIV (showing 82% amino acid identity) correlated with the early classification of Great Island viruses as two distinct serocomplexes (Great Island and Kemerovo serocomplexes). Amino acid identity levels in the VP1(Pol) and T2 proteins between the two serocomplexes were 73 and 82%, respectively, whilst those between previously characterized Orbivirus species are 53-73% and 26-83%, respectively. These data suggest that, despite limited genome segment reassortment between these two groups, their current classification within the same Orbivirus species could be re-evaluated.

Mosquitoes and mosquito-borne arboviruses in the Qinghai-Tibet Plateau--focused on the Qinghai area, China

An investigation was conducted to identify the distribution of mosquitoes and mosquito-borne arboviruses in the Qinghai-Tibet Plateau, China from July to August in 2007. A total of 8,147 mosquitoes representing six species from three genera (Aedes, Culex, and Anopheles) were collected in three locations (Geermu city, altitude of 2,780 m; Xining city, 2,200 m; Minhe county, 1,700 m). Six virus isolates were obtained including Tahyna virus (TAHV), Liaoning virus, and Culex pipiens pallens Densovirus. A serosurvey showed immunoglobulin G antibodies by immunofluorescence assay (IFA) against TAHV in residents of all three locations. The IFA-positive human samples were confirmed by 90% plaque-reduction neutralization tests (PRNT(90)) against TAHV with titers ranging from 1:20 to 1:10,240. In addition, TAHV seropositive cows, sheep, and swine were found in these locations. This investigation represents the first isolation of TAHV from Ae. (Och.) detritus and the first evidence of TAHV infection in residents and livestock in the Qinghai-Tibet Plateau.

Candidates in Astroviruses, Seadornaviruses, Cytorhabdoviruses and Coronaviruses for +1 frame overlapping genes accessed by leaky scanning

BACKGROUND

Overlapping genes are common in RNA viruses where they serve as a mechanism to optimize the coding potential of compact genomes. However, annotation of overlapping genes can be difficult using conventional gene-finding software. Recently we have been using a number of complementary approaches to systematically identify previously undetected overlapping genes in RNA virus genomes. In this article we gather together a number of promising candidate new overlapping genes that may be of interest to the community.

RESULTS

Overlapping gene predictions are presented for the astroviruses, seadornaviruses, cytorhabdoviruses and coronaviruses (families Astroviridae, Reoviridae, Rhabdoviridae and Coronaviridae, respectively).

Isolation and molecular characterization of Banna virus from mosquitoes, Vietnam

We isolated and characterized a Banna virus from mosquitoes in Vietnam; 5 strains were isolated from field-caught mosquitoes at various locations; Banna virus was previously isolated from encephalitis patients in Yunnan, China, in 1987. Together, these findings suggest widespread distribution of this virus throughout Southeast Asia.

Complete characterisation of the American grass carp reovirus genome (genus Aquareovirus: family Reoviridae) reveals an evolutionary link between aquareoviruses and coltiviruses

An aquareovirus was isolated from several fish species in the USA (including healthy golden shiners) that is not closely related to members of species Aquareovirus A, B and C. The virus, which is atypical (does not cause syncytia in cell cultures at neutral pH), was implicated in a winter die-off of grass carp fingerlings and has therefore been called 'American grass carp reovirus' (AGCRV). Complete nucleotide sequence analysis of the AGCRV genome and comparisons to the other aquareoviruses showed that it is closely related to golden ide reovirus (GIRV) (>92% amino acid [aa] identity in VP5(NTPase) and VP2(Pol)). However, comparisons with grass carp reovirus (Aquareovirus C) and chum salmon reovirus (Aquareovirus A) showed only 22% to 76% aa identity in different viral proteins. These findings have formed the basis for the recognition of AGCRV and GIRV as members of a new Aquareovirus species 'Aquareovirus G' by ICTV. Further sequence comparisons to other members of the family Reoviridae suggest that there has been an 'evolutionary jump,' involving a change in the number of genome segments, between the aquareoviruses (11 segments) and coltiviruses (12 segments). Segment 7 of AGRCV encodes two proteins, from two distinct ORFs, which are homologues of two Coltivirus proteins encoded by genome segments 9 and 12. A similar model has previously been reported for the rotaviruses and seadornaviruses.