Caister Academic Press

Insect Virology

"excellently written ... very high standard" (Microbiol. Today)
"a huge leap forward" (SIP)
Publisher: Caister Academic Press
Edited by: Sassan Asgari and Karyn N. Johnson
School of Biological Sciences, The University of Queensland, St Lucia QLD 4072, Australia
Pages: xii + 436
Publication date: September 2010
ISBN: 978-1-904455-71-4
Price: GB £219 or US $250Buy book
Publication date: September 2010
ISBN: 978-1-912530-70-0
Price: US $319Buy ebook

Viruses that are pathogenic to beneficial insects and other arthropods cause millions of dollars of damage to industries such as sericulture, apiculture and aquaculture every year (eg infecting honeybees and silk worms). On the other hand, viruses that are pathogenic to insect pests can be exploited as attractive biological control agents. Another fascinating feature of these viruses is that some, eg baculoviruses, have been commercially exploited for use as gene expression and delivery vectors in both insect and mammalian cells. All of these factors have led to an explosion in the amount of research into insect viruses in recent years generating impressive quantities of information on the molecular and cellular biology of these viruses. This timely book reviews the exciting new developments in the field of insect virology.

Written by internationally renowned insect virologists, chapters review the current molecular biology of all the major groups of insect pathogenic viruses and suggest future directions for research. The book is divided into three parts: 1) DNA viruses 2) RNA viruses and 3) current hot-topics in insect virology. Virus groups covered include: Ascoviruses, Baculoviruses, Densoviruses, Entomopoxviruses, Hytrosaviruses, Iridoviruses, Nudiviruses, Polydnaviruses, Dicistroviruses, Iflaviruses, Nodaviruses, Tetraviruses and Cypoviruses. The special topics chapters review exciting recent developments in insect virology including RNAi, insect antiviral responses, structural comparison of insect RNA viruses, and viral ecology. The book is essential reading for every insect virologist in both the academic and private sectors. It is also strongly recommended for other virologists, particularly those interested in virus evolution, virus structure, viral vectors, biological control of insects and insect immunity.


"excellently written chapters ... a publication of very high standard, useful to experts in the field, but easy enough to introduce the subject to other virologists and students with a basic understanding of virology" from Microbiology Today

"this volume benefits from a huge leap forward in our understanding of the role of RNA silencing in insect virology. In addition, it contains a plethora of sequence data (references) that suggest previously unknown phylogenetic relationships among insect viruses and their families. These two aspects make the volume especially worthwhile to me" from The Society for Invertebrate Pathology Newsletter (November 2011)

Table of contents
1. Ascoviruses
Dennis K. Bideshi, Yves Bigot, Brian A. Federici and Tatsinda Spears
The family Ascoviridae was erected almost a decade ago to accommodate a number of large double-stranded DNA viruses that are pathogenic to larvae and pupae of lepidopterous insects, primarily in the family Noctuidae. Ascoviruses are unique among members of known viral families with regard to their ultrastructure and pathobiology, and among entomoviruses, their mode of transmission is unusual, as they are vectored by parasitoid wasps. Ascovirus virions, for example, exhibit a reticulate pattern when negatively stained, and mature virions are produced by an elaborate process that combines virogenesis and the generation of virion-containing vesicles that accumulate in the blood (haemolymph) of the infected host. The virion vesicles are formed by a novel apoptotic process in which ascoviruses rescue and convert apoptotic bodies into infectious virion factories. These virion vesicles essentially serve as reservoirs for horizontal transmission of ascoviruses to susceptible hosts by female parasitoid wasps during oviposition. Though the study of ascovirus molecular biology is still in its early stages, recent advances in ascovirus molecular genetics and proteomics are beginning to reveal insights into biochemical processes related to their novel structure, pathobiology, and evolutionary origin. In this chapter, a brief historical perspective on the recognition of ascoviruses as a new family of viruses is presented, after which we discuss their evolutionary origin based on molecular profiling of genome sequences and proteomics, and possible mechanisms of virogenesis and the resulting pathology.
2. Baculoviruses: Biology, Replication and Exploitation
Robert D. Possee, Caroline M. Griffiths, Richard B. Hitchman, Adam Chambers, Fernanda Murguia-Meca, John Danquah, Ananya Jeshtadi and Linda A. King
This chapter reviews recent progress to improve our understanding of baculovirus biology and replication at the cellular and whole insect levels, as well as providing an update on the exploitation of these viruses as expression and gene delivery vectors in both insect and mammalian cells. It does not discuss the ecology of baculoviruses, which is reviewed in Chapter 18, nor the use of these viruses as biocontrol agents.
3. Densoviruses: A Highly Diverse Group of Arthropod Parvoviruses
Max Bergoin and Peter Tijssen
Densoviruses (DNVs) are defined as small (25 nm), nonenveloped viruses with an icosahedral symmetry containing an unsegmented single-stranded linear DNA genome, 4-6 kb in length, which terminates in short duplex hairpin telomeres involved in DNA replication. According to these properties, DNVs are bona fide members of the Family Parvoviridae, along with vertebrate parvoviruses. The genome of DNVs contains two sets of genes encoding nonstructural (NS) and capsid (VP) proteins. The manner their coding sequences are organized and transcribed as well as the structure of their noncoding 3' and 5' extremities appear very diversified. Some DNVs have a monosense organization i.e. their gene products are encoded in tandem from a single DNA strand. Others have an ambisense organization, i.e. their NS and VP coding sequences are located in the 5' half on both complementary strands. Most DNVs cause fatal diseases in their hosts. However, mortality is less common for shrimp DNVs. Owing to their specificity and high virulence, they have been considered for the biological control of some major insect pests. The ability of recombinant DNV genomes to integrate into host cell DNA has been exploited for stable transformation of insect cells allowing constitutive expression of foreign genes and somatic transformation of insects.
4. Entomopoxviruses
Srini Perera, Zhen Li, Lillian Pavlik and Basil Arif
Like other poxviruses, entomopoxviruses (EPVs) replicate in the cytoplasm of infected cells but form proteinic bodies (occlusion bodies) in which virions are occluded. Unlike baculoviruses, EPVs appear to utilize haemocytes to disseminate infection to permissive larval cells and tissues. Our observations showed that the tracheal system is not the conduit to spread virus infection in larval tissues. Poxviruses contain a large, linear double stranded DNA genome but in the case of EPVs, the genome is extremely AT-rich. To date, only two EPV genomes have been fully sequenced. Indeed, the very high AT content makes sequencing and assembly a bit of a problem. Comparative analyses of all sequenced poxviruses revealed 49 genes conserved among all poxviruses. The conserved genes are involved in basic functions such as transcription, DNA replication and virion assembly.
5. Hytrosaviruses: Structure and Genomic Properties
Adly M. M. Abd-Alla, Drion G. Boucias and Max Bergoin
Hytrosaviruses are the only insect virus group that elicit salivary gland hypertrophy symptoms in their respective host. Salivary gland hypertrophy viruses (SGHVs) have been identified from several dipteran species, including the tsetse fly Glossina pallidipes (GpSGHV), the house fly Musca domestica (MdSGHV), and the narcissus bulb fly Merodon equestris (MeSGHV). The main characteristics of the hytrosaviruses are: (i) they produce non-occluded, enveloped, rod-shaped virions that measure 550-1000 nm in length and 80-100 nm in diameter; (ii) they possess a large circular double-stranded DNA (dsDNA) genome ranging in size from 120-190 kbp and having G+C ratios ranging from 28-44%; (iii) they cause overt salivary gland hypertrophy symptoms, testicular degeneration and ovarian abnormalities in dipteran adults. Although sharing several important features with other large DNA viruses (baculoviruses, nudiviruses, ascoviruses, and nimaviruses), such as producing rod-shaped, enveloped virions replicating in the nucleus, and possessing a large, circular, double-stranded DNA genome, GpSGHV and MdSGHV (and MeSGHV) differ significantly in several respects from these already-classified viruses. In this chapter, the discovery of the hytrosaviruses and their pathological impact on their host will be discussed and their genomic organization and relation to the other large DNA viruses will be reviewed.
6. Iridoviruses
Trevor Williams and Vernon K. Ward
Invertebrate iridescent viruses (IIVs) of the family Iridoviridae are icosahedral dsDNA viruses with large circularly permuted and terminally redundant genomes that infect a number of agricultural pests, medically important insect vectors and terrestrial isopods that live in damp or aquatic habitats. IIVs currently figure among the most neglected groups of entomopathogenic viruses, although they present a number of unusual and intriguing aspects in their physical properties, replication strategies and host-virus interactions. We present an overview of this group of viruses with emphasis on recent advances and on-going lines of research focussing on the current classification and progress in understanding the structure of IIV virions. We then outline the genomic characteristics and replication process followed by a brief description of their pathology and the ecological factors that determine the distribution and abundance of these viruses. Finally, we summarize future lines for research and identify potential novel applications in biotechnology and materials science.
7. Nudiviruses: Their Biology and Genetics
Johannes A. Jehle
Nudiviruses are a diverse group of rod-shaped viruses with large circular closed dsDNA genomes, which have previously been considered as non-occluded baculoviruses, because of the lack of an occlusion body. In this chapter, the biology as well as recent advances in genome sequencing, analysis of gene function and phylogenetic analyses will be reviewed. These studies revealed that nudiviruses are indeed related to baculoviruses and share a set of 20 core genes involved in virus structural components, virus-host interaction, DNA replication, nucleotide metabolism and RNA replication. As shown in this chapter, the lack of an occlusion body is not a suitable demarcation between nudiviruses and baculoviruses, as some nudiviruses produce an occlusion body.
8. Polydnaviruses
Michael R. Strand
Viruses in the family Polydnaviridae are symbiotically associated with parasitoid wasps in the families Braconidae and Ichneumonidae. Polydnaviruses (PDVs) exist in two forms. In wasps, they persist and are transmitted to offspring as stably integrated proviruses. Replication is restricted to specialized cells in the ovaries of females. This results in production of the encapsidated form of the virus, which wasps inject into hosts when they oviposit. PDVs do not replicate in the wasp's host but they do infect different tissues and express gene products that facilitate successful development of the wasp's offspring. In this chapter, I first discuss the phylogenetic distribution of PDVs in wasps and key features that distinguish the encapsidated form of these viruses. I then review current understanding of how the proviral form of PDVs is organized in the genome of wasps, how PDVs replicate, and the origins of this virus family. I end the chapter with a discussion of the gene products PDVs produce and the role they play in parasitism.
9. Dicistroviruses
Bryony C. Bonning and Karyn N. Johnson
The Dicistroviridae family is comprised of viruses that infect arthropods including beneficial and pest species as well as the model insect Drosophila melanogaster. The 30 nm virions have pseudo T=3 icosahedral symmetry and are non-enveloped. The defining character of this group of viruses is that the two open reading frames encoded by the positive-sense RNA genome are both translated directly from the genomic RNA. This is achieved via two internal ribosome entry sites that independently guide the initiation of translation of the structural and non-structural viral polyproteins; one by elegant molecular mimicry of the initiator tRNA. This chapter describes our current understanding of the molecular biology of these viruses, their interactions with their hosts and potential future impacts of dicistrovirus research.
10. Genomics and Biology of Iflaviruses
Monique M. van Oers
Iflaviruses are insect viruses that form non-enveloped, icosahedral particles approximately 30 nm in diameter. The particles contain one copy of the single-stranded RNA genome, which has a positive polarity. The genome encodes one large polyprotein, which is post-translationally processed. The viral coat proteins are located in an N-terminal domain of the polyprotein, while the non-structural proteins, involved in replication and polyprotein processing, are present in the C-terminal region. The order of the individual proteins in the polyprotein is strictly conserved. Polyprotein translation may initiate at an internal ribosome entry site (IRES) in the 5' untranslated region (UTR) of the RNA. The 3' UTR is followed by a poly(A) tail. Based on genome organization, virion structure and phylogeny, iflaviruses form a distinct group in the order Picornavirales, justifying their classification in a virus family separate from for instance Dicistroviridae and Picornaviridae. The type species of the family Iflaviridae, genus Iflavirus, is infectious flacherie virus (IFV) of silkworms.
11. Insect Nodaviruses
P. Arno Venter, Juan Jovel and Anette Schneemann
Nodaviruses represent a family of small, RNA-containing viruses that naturally infect insects and fish. This review describes recent advances in our understanding of the biology of insect nodaviruses, all of which are currently classified in the genus Alphanodavirus. The small genome size of nodaviruses combined with their abundant proliferation in a wide variety of cells, has allowed their use as model systems for studies on a variety of topics relevant to RNA virology. Many of these studies have been performed with Flock House virus, the most thoroughly characterized insect nodavirus. Here we summarize how research on Flock House virus and other members of this family has shed light on entry, replication and assembly of alphanodaviruses, as well as on mechanisms employed by insect viruses to counter the anti-viral immune responses of their hosts. In addition, we review potential applications of nodaviruses in nanotechnology and nanomedicine.
12. Tetraviruses
Rosemary Ann Dorrington and James Roswell Short
The Tetraviridae are a relatively unknown family of small RNA viruses that exclusively infect the larvae of lepidopteron insect species, many of which are important agricultural pests. While the structure of tetraviral capsids has been well studied, little is known about their biology and the interactions between virus and host that determine their unusually narrow host range and tissue tropism. This is because of the problems associated with developing suitable experimental systems for studying their biology in vivo. This chapter will review recent advances in the understanding of the biology of tetraviruses, highlighting new information on the function and expression of viral translation products and the development of biological systems for elucidating the molecular mechanisms of infection and viral replication.
13. Cypoviruses
Hajime Mori and Peter Metcalf
Cypovirus are members of the Reoviridae family of segmented dsRNA genome viruses which are unique amongst Reoviridae because the infectious forms of the virus are polyhedra, crystalline occlusion bodies containing thousands of virus particles that form in the cytoplasm of infected cells. Polyhedra are micron-size infectious protein crystals which function to protect the virus particles within the crystals from hostile environmental conditions. Polyhedra are stable, only dissolving at pH > 10.5 in the larval midgut, allowing virus particles released from ingested polyhedra to infect the epithelia. Here we briefly review current knowledge of cypovirus and summarize structures of both the virus particle and of polyhedra. The two structures provide a framework for understanding both the formation and stability of polyhedra, and the molecular events that cause virus particles to be incorporated into polyhedra in the cytoplasm of infected cells. This information has been exploited to develop a general method to stabilize proteins by incorporating them into modified polyhedra. We describe these modified polyhedra or 'nano-containers', which have a variety of applications, including the development of stabilized growth factors for cell-culture. Finally we discuss evidence for the possible evolution of cypovirus from members of plant Reoviridae.
14. Structural Comparison of Insect RNA Viruses
Manidipa Banerjee, Jeffrey A Speir and John E Johnson
In recent years, small insect RNA viruses with non-enveloped capsids, such as members of the Nodaviridae, Tetraviridae, Dicistroviridae and Cypoviridae families, have been characterized using X-ray crystallography or cryoelectron microscopy. The capsids of these viruses are icosahedral, with diameters of 30 - 70 nm, and triangulation numbers ranging from 1 to 4 (T=1 to T=4). Viruses packaging single stranded RNA such as nodaviruses, tetraviruses and dicistroviruses contain capsid proteins with closely similar cores comprising an antiparallel β-barrel, jellyroll fold. These capsid proteins undergo analogous post-assembly autocatalytic maturation cleavage. Tetraviruses are unique among this group in containing an immunoglobulin-like domain inserted in their jellyroll capsid proteins, and in undergoing large conformational changes during maturation. Cypoviruses, which package double stranded RNA, have T=2 capsids with structural similarities to the inner shell of reovirus particles. Structural studies of insect RNA viruses have provided valuable information regarding the principles of icosahedral capsid formation, genomic RNA organization, RNA-protein interaction, the mechanism of maturation and associated conformational changes, and the positioning of virus-encoded membrane lytic peptides in capsids. This has resulted in compelling hypotheses regarding capsid disassembly and RNA translocation during infection, some of which have been validated using biochemical and biological studies.
15. Role of MicroRNAs as Regulators of Host-virus Interactions
Sassan Asgari and Christopher S. Sullivan
MicroRNAs (miRNAs) are small non-coding RNA molecules that play a central role in the regulation of gene expression impacting many biological processes. These include development, cancer, apoptosis, immunity, and longevity. In addition, accumulating evidence suggest that miRNAs are likely to be involved in host-virus interactions by modulating expression levels of either defence genes or virus genes. Several groups of animal viruses, as well as insect viruses, encode miRNAs that are instrumental in virus biology, including replication, pathogenesis and latency. In this chapter, we present an overview of the biogenesis of miRNAs, current approaches to the discovery of miRNAs, their mode of action and strategies for determining viral miRNA function.
16. The Antiviral Role of RNA Interference
Michelle L. Flenniken, Mark Kunitomi, Michel Tassetto and Raul Andino
Insects, like all living organisms, have developed defence mechanisms to resist infection. RNA interference (RNAi), a nucleic acid-based, post-transcriptional gene regulation process has recently emerged as a central pathway to anti-viral defence in insects. In this chapter, we outline the role of RNAi in insect immunity and highlight research that led to its discovery as well as research aimed at understanding the mechanistic details of anti-viral RNAi and the counter-measures viruses employ to modulate this immunological mechanism. As our knowledge of the pathways and mechanisms involved in insect immunity expands, so do the opportunities to employ insects as model systems to examine the general principles and co-evolution of hosts and their pathogens.
17. Anti-viral Responses in Insects: Apoptosis and Humoral Responses
Rollie J. Clem, Holly J.R. Popham and Kent S. Shelby
Insects are subject to infection by many different kinds of DNA and RNA viruses. These include viruses that are pathogenic to insects, as well as vertebrate pathogens that are vectored by insects. Although the study of anti-viral responses in insects has lagged behind studies of responses to other types of pathogens, progress in this area has begun to rapidly accelerate over the past several years. Within the field of insect pathology, anti-viral responses in insects have traditionally been categorized as falling into one of three types: physical barriers, cellular immunity, and humoral immunity. However, it has become clear in recent years that a fourth type of response exists, called intracellular immunity. Intracellular immunity is particularly relevant to virus infection because it operates within infected cells, and includes responses such as RNA interference and, as we propose here, apoptosis. In this chapter, we discuss the current understanding of anti-viral responses in insects, focusing mainly on two of the best understood types of responses, apoptosis and humoral immunity.
18. The Ecology of Baculoviruses
Jenny S. Cory
Ecological studies involving insect viruses have centred on baculoviruses, partly because they are associated with population declines of some insect species, and also because they are highly pathogenic to insects, making them ideal candidates for pest control. Recent research has focussed on four main areas; (i) the influence of host condition on resistance to viral infection, (ii) the role and maintenance of baculovirus diversity, (iii) the prevalence of covert infections, and (iv) the elucidation of patterns of host resistance in field populations. Tritrophic interactions, either via direct effects of plant secondary chemicals or through nutritionally mediated changes in host immunity, can have a significant impact on baculovirus efficacy. Variation within baculovirus populations appears to be ubiquitous, and mixed genotype infections apparently act to generate higher levels of pathogenicity. Covert infections are increasingly being shown to be common in field populations of Lepidoptera but their importance in generating overt baculovirus infections is still unclear. Field studies on forest insects indicate that host resistance varies with fluctuating host density and condition. Synthesis of the impacts of host condition on susceptibility, the role of genetic variability in infection, and of the relationship between overt and covert infection, will promote understanding of the ecological interactions between baculoviruses and natural host populations.

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(EAN: 9781904455714 9781912530700 Subjects: [virology] [microbiology] [medical microbiology] [molecular microbiology] [genomics] )