Cricket paralysis virus (CrPV) was initially discovered in Australian field crickets ('' Teleogryllus commodus'' and ''

Teleogryllus oceanicus ''Teleogryllus oceanicus'', commonly known as the Australian, Pacific or oceanic field cricket, is a cricket found across Oceania and in coastal Australia from Carnarvon in Western Australia and Rockhampton in north-east Queensland Otte, D. & Ale ...

'') by Carl Reinganum and his colleagues at the Victorian Plant Research Institute (

Burnley Burnley () is a town and the administrative centre of the wider Borough of Burnley in Lancashire, England, with a 2001 population of 73,021. It is north of Manchester and east of Preston, at the confluence of the River Calder and River Bru ...

Melbourne Melbourne ( ; Boonwurrung/Woiwurrung: ''Narrm'' or ''Naarm'') is the capital and most populous city of the Australian state of Victoria, and the second-most populous city in both Australia and Oceania. Its name generally refers to a met ...

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

). The paralytic disease spread rapidly through a breeding colony as well as through a laboratory population causing about 95% mortality. This was the first recorded isolate of the virus and is generally referred to as CrPVvic to distinguish it from subsequent isolates.

Description

The spheroidal, non-enveloped virus particles of CrPV are about 27 nm diameter in negatively-stained electron micrographs and contain a single piece of positive-sense ssRNA. The virion is composed of four

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

with molecular masses generally reported to be 33, 31 and 30 kilodaltons with a minor VP4 protein of about 8 kDa. The particles resemble those of the mammalian

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

but CrPV virions sediment at a faster rate (167 S) than

poliovirus A poliovirus, the causative agent of polio (also known as poliomyelitis), is a serotype of the species ''Enterovirus C'', in the family of ''Picornaviridae''. There are three poliovirus serotypes: types 1, 2, and 3. Poliovirus is composed of an ...

particles (158 S) in sucrose rate-zonal gradients and, in

isopycnic An isopycnic surface is a surface of constant density inside a fluid. Isopycnic surfaces contrast with isobaric or isothermal surfaces, which describe surfaces of constant pressure and constant temperature respectively. Isopycnic surfaces are s ...

neutral cesium chloride gradients, CrPV particles are denser than those of poliovirus (1.368 g/cm³ vs 1.340 g/cm³ respectively).Christian, P.D. and Scotti, P.D. (2008) "Dicistroviridae". ''Encyclopedia of Virology'' 3rd Edition, Elsevier, London.Scotti, P.D., Longworth, J.F., Plus, N., Croizier, G., and Reinganum, C. (1981). "The biology and ecology of strains of an insect small RNA virus complex". ''Advances in Virus Research'' 26: 117–141.

Range

CrPV has been detected in a number of insect species from at least five different orders of the class Insecta, in both natural and laboratory populations, and is usually identified by standard

serological Serology is the scientific study of serum and other body fluids. In practice, the term usually refers to the diagnostic identification of antibodies in the serum. Such antibodies are typically formed in response to an infection (against a given mi ...

methods. The infections include not only the Australian cricket species but the New Zealand cricket, '' Pteronemobius nigrovus'', as well as the European house cricket, ''

Acheta domesticus ''Acheta domesticus'', commonly called the house cricket, is a cricket most likely native to Southwestern Asia, but between 1950 and 2000 it became the standard feeder insect for the pet and research industries and spread worldwide. They can be ...

''. CrPV does not appear to infect locusts. It is a commonly detected virus in honeybees as an inapparent infection. The strain CrPVbrk was isolated from the cricket ''A. domesticus'' c.1980 following a major population collapse at a cricket rearing farm in Georgia in the US. A related virus from Arkansas, US, initially called '' Pseudoplusia includens'' virus and redesignated CrPVark, was recorded in the mid-1980s. The brk and ark strains are closely related serologically but appear to be very distantly related to the other CrPV isolates so, despite their physical and chemical similarities, it remains speculative that these two American isolates are actually strains of CrPV. Reported detections and/or isolations of CrPV have been made in Australia, New Zealand, the United States, the United Kingdom and Indonesia. CrPV has one of the widest host-ranges of any virus, insect or not. The potential for the use of CrPV as a biological control agent for insects has been suggested. In laboratory experiments CrPVbrk proved to be extremely infectious and pathogenic for adult ''

Ceratitis capitata ''Ceratitis capitata'', commonly known as the Mediterranean fruit fly or medfly, is a yellow-and-brown fly native to sub-Saharan Africa. It has no near relatives in the Western Hemisphere and is considered to be one of the most destructive frui ...

'' (

Mediterranean fruit fly ''Ceratitis capitata'', commonly known as the Mediterranean fruit fly or medfly, is a yellow-and-brown fly native to sub-Saharan Africa. It has no near relatives in the Western Hemisphere and is considered to be one of the most destructive fr ...

). Detailed studies have also been made on the use of a CrPV strain to control the European olive fruit fly (''Dacus oleae'')

American outbreaks

More recently a "cricket paralysis virus" was reported to be involved in other catastrophic collapses in American cricket rearing facilities. A similar report from the UK and European cricket breeders, however, refers to a "cricket paralysis virus" but has identified the causative agent as a small DNA-containing virus, ''Acheta domesticus'' densovirus. Thus these North American outbreaks are probably not due to the small RNA virus taxonomically referred to as CrPV. Over 60 million crickets died as a result of this. Whatever the causative virus, switching to a different species for American breeders is more difficult than it is in Europe, as ''Acheta domesticus'' is currently the only cricket approved for commercial distribution, and any new proposals are scrutinized through a permitting process.

Studies

CrPV has been shown to replicate in continuously cultured cell lines derived from the fruit fly ''

Drosophila melanogaster ''Drosophila melanogaster'' is a species of fly (the taxonomic order Diptera) in the family Drosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the "vinegar fly" or "pomace fly". Starting with Ch ...

'' and other insect cell lines. This ability enabled detailed studies on the replication strategy of the virus. The fact that a demonstrable

cytopathic effect Cytopathic effect or cytopathogenic effect (abbreviated CPE) refers to structural changes in host cells that are caused by viral invasion. The infecting virus causes lysis of the host cell or when the cell dies without lysis due to an inability to ...

was also produced in these cultured cell infections led to the development of sensitive titration assay methods similar to those employed in studies of mammalian picornaviruses. In the 1990s large-scale production of the virus in cell suspension cultures of ''Drosophila'' or ''

Trichoplusia ni The cabbage looper (''Trichoplusia ni'') is a medium-sized moth in the family Noctuidae, a family commonly referred to as owlet moths. Its common name comes from its preferred host plants and distinctive crawling behavior. Cruciferous vegetab ...

'' cells made x-ray

crystallographic Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids. Crystallography is a fundamental subject in the fields of materials science and solid-state physics ( condensed matter physics). The w ...

studies feasible. CrPV was the first insect virus to have its crystal structure determined.Tate, J. Liljas, L., Scotti, P., Christian, P., Lin, T. and Johnson, J.E. (1999). "The crystal structure of cricket paralysis virus: the first view of a new virus family". ''Nature Structural Biology'', 6, 765–774. Early studies conducted in the 1970s and 1980s showed the occurrence of post-translational processing of a large

polyprotein Proteolysis is the breakdown of proteins into smaller polypeptides or amino acids. Uncatalysed, the hydrolysis of peptide bonds is extremely slow, taking hundreds of years. Proteolysis is typically catalysed by cellular enzymes called protease ...

produced during the course of infection of ''Drosophila'' cells with CrPV. This was reminiscent of the post-translational cleavages occurring when mammalian cells are infected with vertebrate picornaviruses such as poliovirus. However, the relative amounts of the resultant proteins resulting from the cleavages were puzzlingly unequal with CrPV in contrast to the equimolar levels produced by picornaviruses. Thus, despite some of the physical and genomic translation similarities that CrPV shared with mammalian picornaviruses, classifying CrPV as an insect "picornavirus" was justifiably contentious. In the later 1990s the elucidation of the crystal structure of CrPV showed that while the conformation of its capsid proteins closely resembled those of picornaviruses, detailed analysis of the complete CrPV genome exposed critical differences. Picornavirus genomes contain only a single

open reading frame In molecular biology, open reading frames (ORFs) are defined as spans of DNA sequence between the start and stop codons. Usually, this is considered within a studied region of a prokaryotic DNA sequence, where only one of the six possible readin ...

(ORF) which is translated into a single polyprotein, but CrPV, as well as several other related insect viruses, is translated from two ORFs each driven by a respective

internal ribosome entry site An internal ribosome entry site, abbreviated IRES, is an RNA element that allows for translation initiation in a cap-independent manner, as part of the greater process of protein synthesis. In eukaryotic translation, initiation typically occurs at t ...

(IRES). Also the capsid proteins are encoded at the 3' end of the CrPV genome, the opposite of that for picornaviruses as well being differently ordered within the genome. These crucial characteristics led to the formation of the family ''

Dicistroviridae ''Dicistroviridae'' is a family of viruses in the order ''Picornavirales''. Invertebrates, including aphids, leafhoppers, flies, bees, ants, and silkworms, serve as natural hosts. There are 15 species in this family, assigned to three genera. Di ...

'' by the

International Committee on Taxonomy of Viruses The International Committee on Taxonomy of Viruses (ICTV) authorizes and organizes the taxonomic classification of and the nomenclatures for viruses. The ICTV has developed a universal taxonomic scheme for viruses, and thus has the means to app ...

(ICTV). CrPV is in the genus ''

Cripavirus ''Cripavirus'' is a genus of viruses in the order ''Picornavirales'', in the family ''Dicistroviridae''. Invertebrates serve as natural hosts. There are four species in this genus. Diseases associated with this genus include: DCV: increased repr ...

'' within this family.Jan, E. "Divergent IRES elements in invertebrates" (2006) ''Virus Research'' 119:16–28

References

External links