Comparison of penaeid shrimp and insect parvoviruses suggests that viral transfers may occur between two distantly related arthropod groups

Bipartite genome and structural organization of the parvovirus Acheta domesticus segmented densovirus

Parvoviruses (family Parvoviridae) are currently defined by a linear monopartite ssDNA genome, T = 1 icosahedral capsids, and distinct structural (VP) and non-structural (NS) protein expression cassettes within their genome. We report the discovery of a parvovirus with a bipartite genome, Acheta domesticus segmented densovirus (AdSDV), isolated from house crickets (Acheta domesticus), in which it is pathogenic. We found that the AdSDV harbors its NS and VP cassettes on two separate genome segments. Its vp segment acquired a phospholipase A2-encoding gene, vpORF3, via inter-subfamily recombination, coding for a non-structural protein. We showed that the AdSDV evolved a highly complex transcription profile in response to its multipartite replication strategy compared to its monopartite ancestors. Our structural and molecular examinations revealed that the AdSDV packages one genome segment per particle. The cryo-EM structures of two empty- and one full-capsid population (3.3, 3.1 and 2.3 Å resolution) reveal a genome packaging mechanism, which involves an elongated C-terminal tail of the VP, "pinning" the ssDNA genome to the capsid interior at the twofold symmetry axis. This mechanism fundamentally differs from the capsid-DNA interactions previously seen in parvoviruses. This study provides new insights on the mechanism behind ssDNA genome segmentation and on the plasticity of parvovirus biology.

Viruses of insects reared for food and feed

The use of insects as food for humans or as feed for animals is an alternative for the increasing high demand for meat and has various environmental and social advantages over the traditional intensive production of livestock. Mass rearing of insects, under insect farming conditions or even in industrial settings, can be the key for a change in the way natural resources are utilized in order to produce meat, animal protein and a list of other valuable animal products. However, because insect mass rearing technology is relatively new, little is known about the different factors that determine the quality and yield of the production process. Obtaining such knowledge is crucial for the success of insect-based product development. One of the issues that is likely to compromise the success of insect rearing is the outbreak of insect diseases. In particular, viral diseases can be devastating for the productivity and the quality of mass rearing systems. Prevention and management of viral diseases imply the understanding of the different factors that interact in insect mass rearing. This publication provides an overview of the known viruses in insects most commonly reared for food and feed. Nowadays with large-scale sequencing techniques, new viruses are rapidly being discovered. We discuss factors affecting the emergence of viruses in mass rearing systems, along with virus transmission routes. Finally we provide an overview of the wide range of measures available to prevent and manage virus outbreaks in mass rearing systems, ranging from simple sanitation methods to highly sophisticated methods including RNAi and transgenics.

Biology, genome organization, and evolution of parvoviruses in marine shrimp

As shrimp aquaculture has evolved from a subsistent farming activity to an economically important global industry, viral diseases have also become a serious threat to the sustainable growth and productivity of this industry. Parvoviruses represent an economically important group of viruses that has greatly affected shrimp aquaculture. In the early 1980s, an outbreak of a shrimp parvovirus, infectious hypodermal and hematopoietic necrosis virus (IHHNV), led to the collapse of penaeid shrimp farming in the Americas. Since then, considerable progress has been made in characterizing the parvoviruses of shrimp and developing diagnostic methods aimed to preventing the spread of diseases caused by these viruses. To date, four parvoviruses are known that infect shrimp; these include IHHNV, hepatopancreatic parvovirus (HPV), spawner-isolated mortality virus (SMV), and lymphoid organ parvo-like virus. Due to the economic repercussions that IHHNV and HPV outbreaks have caused to shrimp farming over the years, studies have been focused mostly on these two pathogens, while information on SMV and LPV remains limited. IHHNV was the first shrimp virus to be sequenced and the first for which highly sensitive diagnostic methods were developed. IHHNV-resistant lines of shrimp were also developed to mitigate the losses caused by this virus. While the losses due to IHHNV have been largely contained in recent years, reports of HPV-induced mortalities in larval stages in hatchery and losses due to reduced growth have increased. This review presents a comprehensive account of the history and current knowledge on the biology, diagnostics methods, genomic features, mechanisms of evolution, and management strategies of shrimp parvoviruses. We also highlighted areas where research efforts should be focused in order to gain further insight on the mechanisms of parvoviral pathogenicity in shrimp that will help to prevent future losses caused by these viruses.

The perils of pathogen discovery: origin of a novel parvovirus-like hybrid genome traced to nucleic acid extraction spin columns

Next-generation sequencing was used for discovery and de novo assembly of a novel, highly divergent DNA virus at the interface between the Parvoviridae and Circoviridae. The virus, provisionally named parvovirus-like hybrid virus (PHV), is nearly identical by sequence to another DNA virus, NIH-CQV, previously detected in Chinese patients with seronegative (non-A-E) hepatitis. Although we initially detected PHV in a wide range of clinical samples, with all strains sharing ∼99% nucleotide and amino acid identity with each other and with NIH-CQV, the exact origin of the virus was eventually traced to contaminated silica-binding spin columns used for nucleic acid extraction. Definitive confirmation of the origin of PHV, and presumably NIH-CQV, was obtained by in-depth analyses of water eluted through contaminated spin columns. Analysis of environmental metagenome libraries detected PHV sequences in coastal marine waters of North America, suggesting that a potential association between PHV and diatoms (algae) that generate the silica matrix used in the spin columns may have resulted in inadvertent viral contamination during manufacture. The confirmation of PHV/NIH-CQV as laboratory reagent contaminants and not bona fide infectious agents of humans underscores the rigorous approach needed to establish the validity of new viral genomes discovered by next-generation sequencing.

Molecular Biology and Epidemiology of Hepatopancreatic parvovirus of Penaeid Shrimp

Hepatopancreatic parvovirus (HPV) is one of the major shrimp parvovirus which is known to cause slow growth in penaeid shrimps. HPV has been found in wild and cultured penaeid shrimps throughout the world and there is high genetic variation among the different geographic isolates/host species. Given its high prevalence, wide distribution and ability to cause considerable economic loss in shrimp aquaculture industry, HPV deserves more attention than it has received. Till date, a total of four complete genome sequences of HPV have been reported in addition to a large number of partial sequences. HPV infection is seldom observed alone in epizootics and has occurred in multiple infections with other more pathogenic viruses and in most cases, heavy infections result in no visible inflammatory response. A great deal of information has accumulated in recent years on the clinical signs, geographical distribution, transmission and genetic diversity of HPV infection in shrimp aquaculture. However, the mechanism by which HPV enters the shrimp tissues and pathogenesis of virus is still unknown. To date, no effective prophylactic measures are available to reduce the infection in shrimps. To control and prevent HPV infection, considerable research efforts are on. This review provides information on current knowledge on HPV infection in penaeid shrimp aquaculture.

Complete nucleotide sequence analysis of a Korean strain of hepatopancreatic parvovirus (HPV) from Fenneropenaeus chinensis

Hepatopancreatic parvovirus (HPV) of shrimp is distributed worldwide and the entire genome of Thailand and Indian strains (PmDNV) and one Australian strain (PmergDNV) have now been reported. The complete nucleotide sequence of a HPV strain isolated from the fleshy prawn Fenneropenaeus chinensis in Korea (FcDNV) was determined and compared to previously reported sequences. The entire genome of FcDNV contains 6,336 nucleotides, with 40% G+C content, which is the biggest of the known HPV strains. The HPV genome has three open reading frames (ORFs) with a slight overlap between the first and second ORFs. The three ORFs encode the NS2 and NS1 proteins and VP that consist of 425, 578, and 820 amino acids, respectively. Among the three proteins, the NS1 protein shows the highest sequence similarity to the NS1 protein of other known HPV strains, followed by the NS2 protein and the VP protein. Phylogenetic analyses showed that HPV can be grouped into three genotypes, as previously reported, and FcDNV can be grouped as genotype I, with HPV strains isolated in Madagascar and Tanzania. The nucleotide sequences of the noncoding regions at the 5'- and 3'-ends of the plus-strand genome showed a Y-shaped hairpin structure and simple hairpin structure, respectively.

Widespread endogenization of densoviruses and parvoviruses in animal and human genomes

Parvoviruses infect humans and a broad range of animals, from mammals to crustaceans, and generally are associated with a variety of acute and chronic diseases. However, many others cause persistent infections and are not known to be associated with any disease. Viral persistence is likely related to the ability to integrate into the chromosomal DNA and to establish a latent infection. However, there is little evidence for genome integration of parvoviral DNA except for Adeno-associated virus (AAV). Here we performed a systematic search for homologs of parvoviral proteins in publicly available eukaryotic genome databases followed by experimental verification and phylogenetic analysis. We conclude that parvoviruses have frequently invaded the germ lines of diverse animal species, including mammals, fishes, birds, tunicates, arthropods, and flatworms. The identification of orthologous endogenous parvovirus sequences in the genomes of humans and other mammals suggests that parvoviruses have coexisted with mammals for at least 98 million years. Furthermore, some of the endogenized parvoviral genes were expressed in eukaryotic organisms, suggesting that these viral genes are also functional in the host genomes. Our findings may provide novel insights into parvovirus biology, host interactions, and evolution.

Simple immunoblot and immunohistochemical detection of Penaeus stylirostris densovirus using monoclonal antibodies to viral capsid protein expressed heterologously

Penaeus stylirostris densovirus (PstDNV), called formerly infectious hypodermal and hematopoietic necrosis virus (IHHNV), is an important shrimp pathogen which can cause mortality in the blue shrimp Penaeus (Litopenaeus) stylirostris and stunting in the whiteleg shrimp Penaeus (Litopenaeus) vannamei. Five monoclonal antibodies (MAbs) were produced against the 37kDa capsid protein 3 (CP3) of PstDNV expressed heterologously in the form of a fusion protein with glutathione-S-transferase called GST-CP3. All MAbs belonged to the IgG2b subclass and could bind to GST-CP3 at 300 pg/spot in immunodot-blot tests. They could detect CP3 in naturally infected shrimp extracts by Western blotting and dot blotting and in shrimp tissues by immunohistochemistry without cross-reactivity to extracts from uninfected shrimps or shrimps infected with several other viruses. Although dot blot assay sensitivity was approximately 1000 times lower than that of one step PCR for PstDNV, it easily detected PstDNV infections in field samples of Penaeus monodon and Penaeus vannamei.

Viral disease emergence in shrimp aquaculture: origins, impact and the effectiveness of health management strategies

Shrimp aquaculture has grown rapidly over several decades to become a major global industry that serves the increasing consumer demand for seafood and has contributed significantly to socio-economic development in many poor coastal communities. However, the ecological disturbances and changes in patterns of trade associated with the development of shrimp farming have presented many of the pre-conditions for the emergence and spread of disease. Shrimp are displaced from their natural environments, provided artificial or alternative feeds, stocked in high density, exposed to stress through changes in water quality and are transported nationally and internationally, either live or as frozen product. These practices have provided opportunities for increased pathogenicity of existing infections, exposure to new pathogens, and the rapid transmission and transboundary spread of disease. Not surprisingly, a succession of new viral diseases has devastated the production and livelihoods of farmers and their sustaining communities. This review examines the major viral pathogens of farmed shrimp, the likely reasons for their emergence and spread, and the consequences for the structure and operation of the shrimp farming industry. In addition, this review discusses the health management strategies that have been introduced to combat the major pathogens and the reasons that disease continues to have an impact, particularly on poor, small-holder farmers in Asia.

Isolation and characterization of the full coding sequence of a novel densovirus from the mosquito Culex pipiens pallens

During an investigation of arboviruses in China, a novel densovirus (DNV) was isolated from the adult female Culex pipiens pallens. The virus, designated Culex pipiens pallens densovirus (CppDNV), caused cytopathic effect in C6/36 cells. The virus particles were icosahedral, non-enveloped and had a mean diameter of 24 nm. The complete coding region of CppDNV was found to be 3335 nt and it contained three open reading frames (ORFs). CppDNV shares 82-93 % identical nucleotides with isolates of the Aedes albopictus densovirus [isolates AalDNV-1, AalDNV-2 (C6/36 DNV) and AalDNV-3], Aedes aegypti densovirus (AaeDNV) and Haemagogus equines densovirus (HeDNV). The nucleotide sequence identity among CppDNV isolates exceeds 98 %. Phylogenetic trees based on non-structural (NS1 and NS2) and capsid (VP) genes show that CppDNV clustered with the species AaeDNV and represents a novel variant of this species within the genus Brevidensovirus.

Molecular characterisation of hepatopancreatic parvovirus (PmergDNV) from Australian Penaeus merguiensis

Hepatopancreatic parvovirus infection is associated with reduced growth rates of prawns during the juvenile stages and overt mortalities. Hepatopancreatic parvovirus was purified from Penaeus merguiensis from northern Queensland and a partial consensus sequence of 5.9 kb was obtained. Nucleotide comparisons revealed that the Australian isolate of HPV has a nucleotide similarity (87%) closer to HPVchin and the full sequence of HPV Penaeus monodon (PmDNV) (6321 bp) than to HPVsemi (83%). Three putative open reading frames were identified. The first open reading frame encoded a nonstructural protein (NS2) and shared an amino acid similarity of 86% with PmDNV. The second ORF overlapped the first open reading frame and shared 93% and 26% amino acid similarity with PmDNV and PstDNV, respectively, and encoded NS1. The third ORF encoded the viral structural protein and shared an amino acid similarity of 73% with the capsid protein of PmDNV and HPVchin. The phylogeny suggests that the Australian HPV isolate is closely related to the Korean HPVchin isolate than to the Indian HPVsemi and Thai PmDNV isolates. HPV strains may be following the phylogenetic relationship of penaeid prawn hosts rather than their geography.

Parvovirus variation for disease: a difference with RNA viruses?

The Parvoviridae, a family of viruses with single-stranded DNA genomes widely spread from invertebrates to mammal and human hosts, display a remarkable evolutionary capacity uncommon in DNA genomes. Parvovirus populations show high genetic heterogeneity and large population sizes resembling the quasispecies found in RNA viruses. These viruses multiply in proliferating cells, causing acute, persistent or latent infections relying in the immunocompetence and developmental stage of the hosts. Some parvovirus populations in natural settings, such as carnivore autonomous parvoviruses or primate adeno associated virus, show a high degree of genetic heterogeneity. However, other parvoviruses such as the pathogenic B19 human erythrovirus or the porcine parvovirus, show little genetic variation, indicating different virus-host relationships. The Parvoviridae evolutionary potential in mammal infections has been modeled in the experimental system formed by the immunodeficient scid mouse infected by the minute virus of mice (MVM) under distinct immune and adaptive pressures. The sequence of viral genomes (close to 10(5) nucleotides) in emerging MVM pathogenic populations present in the organs of 26 mice showed consensus sequences not representing the complex distribution of viral clones and a high genetic heterogeneity (average mutation frequency 8.3 x 10(-4) substitutions/nt accumulated over 2-3 months). Specific amino acid changes, selected at a rate up to 1% in the capsid and in the NS2 nonstructural protein, endowed these viruses with new tropism and increased fitness. Further molecular analysis supported the notion that, in addition to immune pressures, the affinity of molecular interactions with cellular targets, as the Crml nuclear export receptor or the primary capsid receptor, as well as the adaptation to tissues enriched in proliferating cells, are major selective factors in the rapid parvovirus evolutionary dynamics.