Isolation and characterization of an iridovirus from Hermann's tortoises (Testudo hermanni)

Emerging infectious diseases of chelonians

Various new diseases have emerged in captive and wild populations of turtles and tortoises. Several of these seem to be on the rise and have the potential to cause widespread disease. This article reviews the current literature and authors' experience with intranuclear coccidiosis, cryptosporidium, iridovirus, and adenovirus. The biology, epidemiology, clinical signs, diagnosis, treatment, and pathologic changes are described for each disease.

Tolerance of fungal infection in European water frogs exposed to Batrachochytrium dendrobatidis after experimental reduction of innate immune defenses

Background

While emerging diseases are affecting many populations of amphibians, some populations are resistant. Determining the relative contributions of factors influencing disease resistance is critical for effective conservation management. Innate immune defenses in amphibian skin are vital host factors against a number of emerging pathogens such as ranaviruses and the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd). Adult water frogs from Switzerland (Pelophylax esculentus and P. lessonae) collected in the field with their natural microbiota intact were exposed to Bd after experimental reduction of microbiota, skin peptides, both, or neither to determine the relative contributions of these defenses.

Results

Naturally-acquired Bd infections were detected in 10/51 P. lessonae and 4/19 P. esculentus, but no disease outbreaks or population declines have been detected at this site. Thus, this population was immunologically primed, and disease resistant. No mortality occurred during the 64 day experiment. Forty percent of initially uninfected frogs became sub-clinically infected upon experimental exposure to Bd. Reduction of both skin peptide and microbiota immune defenses caused frogs to gain less mass when exposed to Bd than frogs in other treatments. Microbiota-reduced frogs increased peptide production upon Bd infection. Ranavirus was undetectable in all but two frogs that appeared healthy in the field, but died within a week under laboratory conditions. Virus was detectable in both toe-clips and internal organs.

Conclusion

Intact skin microbiota reduced immune activation and can minimize subclinical costs of infection. Tolerance of Bd or ranavirus infection may differ with ecological conditions.

Environmental persistence of amphibian and reptilian ranaviruses

Ranaviruses infect fish, amphibians, and reptiles. The present study was conducted to compare the persistence of amphibian and reptilian ranaviruses in a pond habitat. The 4 viruses used in this study included 2 amphibian ranaviruses, Frog virus 3 (FV3, the type species of the genus Ranavirus) and an isolate from a frog, and 2 ranaviruses of reptilian origin (from a tortoise and from a gecko). A sandwich germ-carrier technique was used to study the persistence of these viruses in sterile and unsterile pond water (PW) and soil obtained from the bank of a pond. For each virus, virus-loaded carriers were placed in each of the 3 substrates, incubated at 4 and 20°C, and titrated at regular intervals. Serial data were analyzed using a linear regression model to calculate T-90 values (time required for 90% reduction in the virus titer). Resistance of the viruses to drying was also studied. All 4 viruses were resistant to drying. At 20°C, T-90 values of the viruses were 22 to 31 d in sterile PW and 22 to 34 d in unsterile PW. Inactivation of all 4 viruses in soil at this temperature appeared to be non-linear. T-90 values at 4°C were 102 to 182 d in sterile PW, 58 to 72 d in unsterile PW, and 30 to 48 d in soil. Viral persistence was highest in the sterile PW, followed by the unsterile PW, and was lowest in soil. There were no significant differences in the survival times between the amphibian and reptilian viruses. The results of the present study suggest that ranaviruses can survive for long periods of time in pond habitats at low temperatures.

Viruses infecting reptiles

A large number of viruses have been described in many different reptiles. These viruses include arboviruses that primarily infect mammals or birds as well as viruses that are specific for reptiles. Interest in arboviruses infecting reptiles has mainly focused on the role reptiles may play in the epidemiology of these viruses, especially over winter. Interest in reptile specific viruses has concentrated on both their importance for reptile medicine as well as virus taxonomy and evolution. The impact of many viral infections on reptile health is not known. Koch's postulates have only been fulfilled for a limited number of reptilian viruses. As diagnostic testing becomes more sensitive, multiple infections with various viruses and other infectious agents are also being detected. In most cases the interactions between these different agents are not known. This review provides an update on viruses described in reptiles, the animal species in which they have been detected, and what is known about their taxonomic positions.

Major capsid protein gene sequence analysis of the Santee-Cooper ranaviruses DFV, GV6, and LMBV

The Santee-Cooper ranaviruses doctor fish virus (DFV), guppy virus 6 (GV6), and largemouth bass virus (LMBV) are members of the genus Ranavirus within the family Iridoviridae. The major capsid protein (MCP) is a main structural protein of iridoviruses and supports the differentiation and classification of ranaviruses. Presently the complete sequence of the MCP gene is known for most ranaviruses with the exception of the Santee-Cooper ranaviruses. In the present study, the complete nucleotide sequence of the MCP gene of DFV, GV6, and LMBV was determined. DFV and GV6 are identical within the MCP gene sequence. The identity compared to the corresponding sequence in LMBV amounts to 99.21%. The MCP gene of DFV, GV6, and LMBV exhibits only approximately 78% identity compared to the respective gene of other ranaviruses. Based on the sequence data obtained in the present study, a Rana MCP polymerase chain reaction (PCR) and subsequent restriction fragment length polymorphism (RFLP) analysis were developed to identify and differentiate ranaviruses, including DFV, GV6, and LMBV.

Viruses in reptiles

The etiology of reptilian viral diseases can be attributed to a wide range of viruses occurring across different genera and families. Thirty to forty years ago, studies of viruses in reptiles focused mainly on the zoonotic potential of arboviruses in reptiles and much effort went into surveys and challenge trials of a range of reptiles with eastern and western equine encephalitis as well as Japanese encephalitis viruses. In the past decade, outbreaks of infection with West Nile virus in human populations and in farmed alligators in the USA has seen the research emphasis placed on the issue of reptiles, particularly crocodiles and alligators, being susceptible to, and reservoirs for, this serious zoonotic disease. Although there are many recognised reptilian viruses, the evidence for those being primary pathogens is relatively limited. Transmission studies establishing pathogenicity and cofactors are likewise scarce, possibly due to the relatively low commercial importance of reptiles, difficulties with the availability of animals and permits for statistically sound experiments, difficulties with housing of reptiles in an experimental setting or the inability to propagate some viruses in cell culture to sufficient titres for transmission studies. Viruses as causes of direct loss of threatened species, such as the chelonid fibropapilloma associated herpesvirus and ranaviruses in farmed and wild tortoises and turtles, have re-focused attention back to the characterisation of the viruses as well as diagnosis and pathogenesis in the host itself.

1. Introduction

2. Methods for working with reptilian viruses

3. Reptilian viruses described by virus families

3.1. Herpesviridae

3.2. Iridoviridae

3.2.1 Ranavirus

3.2.2 Erythrocytic virus

3.2.3 Iridovirus

3.3. Poxviridae

3.4. Adenoviridae

3.5. Papillomaviridae

3.6. Parvoviridae

3.7. Reoviridae

3.8. Retroviridae and inclusion body disease of Boid snakes

3.9. Arboviruses

3.9.1. Flaviviridae

3.9.2. Togaviridae

3.10. Caliciviridae

3.11. Picornaviridae

3.12. Paramyxoviridae

4. Summary

5. Acknowledgements

6. Competing interests

7. References

Host range, host specificity and hypothesized host shift events among viruses of lower vertebrates

The successful replication of a viral agent in a host is a complex process that often leads to a species specificity of the virus and can make interspecies transmission difficult. Despite this difficulty, natural host switch seems to have been frequent among viruses of lower vertebrates, especially fish viruses, since there are several viruses known to be able to infect a wide range of species. In the present review we will focus on well documented reports of broad host range, variations in host specificity, and host shift events hypothesized for viruses within the genera Ranavirus, Novirhabdovirus, Betanodavirus, Isavirus, and some herpesvirus.

The chelonian respiratory system

This article reviews anatomy, physiology, diagnostic techniques, and specific disease syndromes of the chelonian respiratory system. Respiratory disease is common in chelonians and is a cause of significant morbidity and mortality in these animals. Mycoplasma, herpesvirus, and iridovirus are reviewed in depth.

Innate immune evasion mediated by the Ambystoma tigrinum virus eukaryotic translation initiation factor 2alpha homologue

Ranaviruses (family Iridoviridae, genus Ranavirus) are large, double-stranded DNA (dsDNA) viruses whose replication is restricted to ectothermic vertebrates. Many highly pathogenic members of the genus Ranavirus encode a homologue of the eukaryotic translation initiation factor 2α (eIF2α). Data in a heterologous vaccinia virus system suggest that the Ambystoma tigrinum virus (ATV) eIF2α homologue (vIF2αH; open reading frame [ORF] 57R) is involved in evading the host innate immune response by degrading the interferon-inducible, dsRNA-activated protein kinase, PKR. To test this hypothesis directly, the ATV vIF2αH gene (ORF 57R) was deleted by homologous recombination, and a selectable marker was inserted in its place. The ATVΔ57R virus has a small plaque phenotype and is 8-fold more sensitive to interferon than wild-type ATV (wtATV). Infection of fish cells with the ATVΔ57R virus leads to eIF2α phosphorylation, in contrast to infection with wtATV, which actively inhibits eIF2α phosphorylation. The inability of ATVΔ57R to prevent phosphorylation of eIF2α correlates with degradation of fish PKZ, an interferon-inducible enzyme that is closely related to mammalian PKR. In addition, salamanders infected with ATVΔ57R displayed an increased time to death compared to that of wtATV-infected salamanders. Therefore, in a biologically relevant system, the ATV vIF2αH gene acts as an innate immune evasion factor, thereby enhancing virus pathogenesis.

Iridovirus infections in finfish - critical review with emphasis on ranaviruses

Viruses in three genera of the family Iridoviridae (iridoviruses) affect finfish. Ranaviruses and megalocytiviruses are recently emerged pathogens. Both cause severe systemic disease, occur globally and affect a diversity of hosts. In contrast, lymphocystiviruses cause superficial lesions and rarely cause economic loss. The ranavirus epizootic haematopoietic necrosis virus (EHNV) from Australia was the first iridovirus to cause epizootic mortality in finfish. Like other ranaviruses, it lacks host specificity. A distinct but closely related virus, European catfish virus, occurs in finfish in Europe, while very similar ranaviruses occur in amphibians in Europe, Asia, Australia, North America and South America. These viruses can be distinguished from one another by conserved differences in the sequence of the major capsid protein gene, which informs policies of the World Organisation for Animal Health to minimize transboundary spread of these agents. However, limited epidemiological information and variations in disease expression create difficulties for design of sampling strategies for surveillance. There is still uncertainty surrounding the taxonomy of some putative ranaviruses such as Singapore grouper iridovirus and Santee-Cooper ranavirus, both of which cause serious disease in fish, and confusion continues with diseases caused by megalocytiviruses. In this review, aspects of the agents and diseases caused by ranaviruses are contrasted with those due to megalocytiviruses to promote accurate diagnosis and characterization of the agents responsible. Ranavirus epizootics in amphibians are also discussed because of possible links with finfish and common anthropogenic mechanisms of spread. The source of the global epizootic of disease caused by systemic iridoviruses in finfish and amphibians is uncertain, but three possibilities are discussed: trade in food fish, trade in ornamental fish, reptiles and amphibians and emergence from unknown reservoir hosts associated with environmental change.

Evidence for multiple recent host species shifts among the Ranaviruses (family Iridoviridae)

Members of the genus Ranavirus (family Iridoviridae) have been recognized as major viral pathogens of cold-blooded vertebrates. Ranaviruses have been associated with amphibians, fish, and reptiles. At this time, the relationships between ranavirus species are still unclear. Previous studies suggested that ranaviruses from salamanders are more closely related to ranaviruses from fish than they are to ranaviruses from other amphibians, such as frogs. Therefore, to gain a better understanding of the relationships among ranavirus isolates, the genome of epizootic hematopoietic necrosis virus (EHNV), an Australian fish pathogen, was sequenced. Our findings suggest that the ancestral ranavirus was a fish virus and that several recent host shifts have taken place, with subsequent speciation of viruses in their new hosts. The data suggesting several recent host shifts among ranavirus species increase concern that these pathogens of cold-blooded vertebrates may have the capacity to cross numerous poikilothermic species barriers and the potential to cause devastating disease in their new hosts.

Development and use of an indirect enzyme-linked immunosorbent assay for detection of iridovirus exposure in gopher tortoises (Gopherus polyphemus) and eastern box turtles (Terrapene carolina carolina)

Iridoviruses, pathogens typically associated with fish and amphibians, have recently been shown to cause acute respiratory disease in chelonians including box turtles, red-eared sliders, gopher tortoises, and Burmese star tortoises. Case reports of natural infections in several chelonian species in the United States have been reported, however the prevalence remains unknown in susceptible populations of free-ranging chelonians. To determine the prevalence of iridovirus exposure in free-ranging gopher tortoises (Gopherus polyphemus) in the southeast United States, an indirect enzyme-linked immunosorbent assay (ELISA) was developed and used to evaluate plasma samples from wild gopher tortoises (G. polyphemus) from: Alabama (n=9); Florida (n=658); Georgia (n=225); Louisiana (n=12); Mississippi (n=28); and unknown locations (68) collected between 2001 and 2006. Eight (1.2%) seropositive tortoises were identified from Florida and seven (3.1%) from Georgia for an overall prevalence of 1.5%. Additionally, a population of eastern box turtles was sampled from a private nature sanctuary in Pennsylvania that experienced an outbreak of iridovirus the previous year, which killed 16 turtles. Only 1 turtle out of 55 survivors tested positive (1.8%). Results suggest a low exposure rate in chelonians to this pathogen; however, it is suspected that this is an underestimate of the true prevalence. Since experimental transmission studies and past outbreaks have shown a high rate of mortality in infected turtles, turtles may die before they develop an antibody response. Further, the duration of the antibody response is unknown and may also cause an underestimate of the true prevalence.

Complete sequence determination of a novel reptile iridovirus isolated from soft-shelled turtle and evolutionary analysis of Iridoviridae

Background

Soft-shelled turtle iridovirus (STIV) is the causative agent of severe systemic diseases in cultured soft-shelled turtles (Trionyx sinensis). To our knowledge, the only molecular information available on STIV mainly concerns the highly conserved STIV major capsid protein. The complete sequence of the STIV genome is not yet available. Therefore, determining the genome sequence of STIV and providing a detailed bioinformatic analysis of its genome content and evolution status will facilitate further understanding of the taxonomic elements of STIV and the molecular mechanisms of reptile iridovirus pathogenesis.

Results

We determined the complete nucleotide sequence of the STIV genome using 454 Life Science sequencing technology. The STIV genome is 105 890 bp in length with a base composition of 55.1% G+C. Computer assisted analysis revealed that the STIV genome contains 105 potential open reading frames (ORFs), which encode polypeptides ranging from 40 to 1,294 amino acids and 20 microRNA candidates. Among the putative proteins, 20 share homology with the ancestral proteins of the nuclear and cytoplasmic large DNA viruses (NCLDVs). Comparative genomic analysis showed that STIV has the highest degree of sequence conservation and a colinear arrangement of genes with frog virus 3 (FV3), followed by Tiger frog virus (TFV), Ambystoma tigrinum virus (ATV), Singapore grouper iridovirus (SGIV), Grouper iridovirus (GIV) and other iridovirus isolates. Phylogenetic analysis based on conserved core genes and complete genome sequence of STIV with other virus genomes was performed. Moreover, analysis of the gene gain-and-loss events in the family Iridoviridae suggested that the genes encoded by iridoviruses have evolved for favoring adaptation to different natural host species.

Conclusion

This study has provided the complete genome sequence of STIV. Phylogenetic analysis suggested that STIV and FV3 are strains of the same viral species belonging to the Ranavirus genus in the Iridoviridae family. Given virus-host co-evolution and the phylogenetic relationship among vertebrates from fish to reptiles, we propose that iridovirus might transmit between reptiles and amphibians and that STIV and FV3 are strains of the same viral species in the Ranavirus genus.

Characterization of a late gene encoding for MCP in soft-shelled turtle iridovirus (STIV)

Major caspid protein (MCP) is the major structural component of virus particles and revealed to be very responsible for classification of new tentative iridovirus isolates. In this paper, the complete sequences of MCP gene was firstly identified and characterized from soft-shelled turtle iridovirus (STIV). The MCP, classified as a late transcript by drug inhibition, encodes a protein of 463 aa with a predicted molecular weight of 50kDa. Indirect immunofluorescence (IIF) and virus neutralization assay were developed to determine the sensitivity and virus neutralizing activity of MCP-specific antiserum. Furthermore, the MCP temporal expression pattern during STIV infection in vitro was characterized by Western blot and RT-PCR assays. The results suggest that STIV could be classified as a member of genus Ranavirus in family Iridoviridae and has cell-type-specific programs of viral gene expression.

ISOLATION OF A RANAVIRUS FROM A GECKO (UROPLATUS FIMBRIATUS)

A virus was isolated from the liver and stomach of a leaf-tailed gecko (Uroplatus fimbriatus) with granulomatous lesions on the tongue and hepatitis. The virus was identified as an iridovirus on the basis of morphology by electron microscopy, restriction endonuclease assay, and sequencing of a large portion of the major capsid protein gene. Comparative analysis revealed that this isolate is related to frog virus 3, the type species of the genus Ranavirus.

Identification of a Bohle iridovirus thymidine kinase gene and demonstration of activity using vaccinia virus

In recent years interest in the family Iridoviridae has been renewed by the identification of a number of viruses, particularly from the genus Ranavirus, associated with disease in a range of poikilotherms. Ranaviruses have been isolated from amphibian, piscine and reptilian species. Here we describe an open reading frame (ORF) identified in the genome of Bohle iridovirus (BIV) which contains a nucleotide binding motif conserved within the thymidine kinase (TK) genes of iridoviruses from other genera (lymphocystis disease virus, LCDV, type species of the genus Lymphocystivirus; Chilo iridescent virus, CIV, type species of the genus Iridovirus). The ability of this putative gene to express a functional TK was confirmed by rescue of a TK negative mutant vaccinia virus in the presence of selective media, when expression was controlled by a vaccinia virus promoter. The sequence of the BIV TK was compared with the homologous sequences from epizootic haematopoietic necrosis virus (EHNV), a virus associated with disease in fish, from Wamena iridovirus (WIV) associated with systemic disease in green pythons, and from frog virus 3 (FV3) the ranavirus type species. Comparisons between these sequences and those available from other ranaviruses, other iridoviruses, other DNA viruses and cellular TKs are presented.

Reptile virology

Reptiles are hosts to diverse viral infections. This article reviews the viruses that are known to infect reptiles and discusses associated pathology, available diagnostic methods, and management techniques for the reptile clinician.

Varanid herpesvirus 1: a novel herpesvirus associated with proliferative stomatitis in green tree monitors (Varanus prasinus)

Stomatitis is a common problem in lizards, and the etiologies of stomatitis in lizards are not well understood. Four green tree monitor lizards (Varanus prasinus) from two different collections were evaluated because of proliferative stomatitis. Degenerate PCR primers targeting a conserved region of herpesvirus DNA-dependent DNA polymerase were used to amplify and sequence a product from gingival tissue of three of four lizards (cases 1, 3, and 4). DNA in situ hybridization of tissues from three lizards was positive for herpesvirus in the oral mucosa of all three lizards tested (cases 1-3) and the brain of two lizards (cases 1 and 3). Comparative sequence analysis suggests that this virus is a novel member of the subfamily alpha-herpesvirinae, and is here termed varanid herpesvirus 1.

Evidence for emergence of an amphibian iridoviral disease because of human-enhanced spread

Our understanding of origins and spread of emerging infectious diseases has increased dramatically because of recent applications of phylogenetic theory. Iridoviruses are emerging pathogens that cause global amphibian epizootics, including tiger salamander (Ambystoma tigrinum) die-offs throughout western North America. To explain phylogeographical relationships and potential causes for emergence of western North American salamander iridovirus strains, we sequenced major capsid protein and DNA methyltransferase genes, as well as two noncoding regions from 18 geographically widespread isolates. Phylogenetic analyses of sequence data from the capsid protein gene showed shallow genetic divergence (< 1%) among salamander iridovirus strains and monophyly relative to available fish, reptile, and other amphibian iridovirus strains from the genus Ranavirus, suggesting a single introduction and radiation. Analysis of capsid protein sequences also provided support for a closer relationship of tiger salamander virus strains to those isolated from sport fish (e.g. rainbow trout) than other amphibian isolates. Despite monophyly based on capsid protein sequences, there was low genetic divergence among all strains (< 1.1%) based on a supergene analysis of the capsid protein and the two noncoding regions. These analyses also showed polyphyly of strains from Arizona and Colorado, suggesting recent spread. Nested clade analyses indicated both range expansion and long-distance colonization in clades containing virus strains isolated from bait salamanders and the Indiana University axolotl (Ambystoma mexicanum) colony. Human enhancement of viral movement is a mechanism consistent with these results. These findings suggest North American salamander ranaviruses cause emerging disease, as evidenced by apparent recent spread over a broad geographical area.

RANAVIRUS-ASSOCIATED MORBIDITY AND MORTALITY IN A GROUP OF CAPTIVE EASTERN BOX TURTLES (TERRAPENE CAROLINA CAROLINA)

Seven captive eastern box turtles (Terrapene carolina carolina) from a large collection of North American chelonians in North Carolina became acutely ill in the fall of 2002. Five of the turtles died. Clinical signs included cutaneous abscessation, oral ulceration or abscessation (or both), respiratory distress, anorexia, and lethargy. The predominant postmortem lesion was fibrinoid vasculitis of various organs, including skin, mucous membranes, lungs, and liver. No inclusion bodies were detected by histopathology or electron microscopy of formalin-fixed tissue. An iridovirus was isolated from tissues obtained postmortem from two of the box turtles that died. The virus was characterized by electron microscopy, polymerase chain reaction, and sequence analysis of a portion of the major capsid protein as a member of the genus Ranavirus.

Comparative genomic analyses of frog virus 3, type species of the genus Ranavirus (family Iridoviridae)

Frog virus 3 (FV3) is the type species member of the genus Ranavirus (family Iridoviridae). To better understand the molecular mechanisms involved in the replication of FV3, including transcription of its highly methylated DNA genome, we have determined the complete nucleotide sequence of the FV3 genome. The FV3 genome is 105903 bp long excluding the terminal redundancy. The G + C content of FV3 genome is 55% and it encodes 98 nonoverlapping potential open reading frames (ORFs) containing 50-1293 amino acids. Eighty-four ORFs have significant homology to known proteins of other iridoviruses, whereas twelve of these unique FV3 proteins do not share homology to any known protein. A microsatellite containing a stretch of 34 tandemly repeated CA dinucleotide in a noncoding region was detected. To date, no such sequence has been reported in any animal virus.

Sequence analysis of the complete genome of an iridovirus isolated from the tiger frog

We have isolated a tiger frog virus (TFV) from diseased tiger frogs, Rana tigrina rugulosa. The genome was a linear double-stranded DNA of 105,057 basepairs in length with a base composition of 55.01% G+C. About 105 open reading frames were identified with coding capacities for polypeptides ranging from 40 to 1294 amino acids. Computer-assisted analyses of the deduced amino acid sequences revealed that 39 of 105 putative gene products showed significant homology to functionally characterized proteins of other species in the GenBank/EMBL/DDBJ databases. These proteins included enzymes and structural proteins involved in virus replication, transcription, modification, and virus--host interaction. The deduced amino acid sequences of TFV gene products showed more than 90% identity to FV3, but a low degree of similarity among TFV, ISKNV, and LCDV-1. The results from this study indicated that TFV may belong to the genus Ranavirus of the family Iridoviridae.

Occurrence of an invertebrate iridescent-like virus (Iridoviridae) in reptiles

Viral isolates were obtained in 1998, 1999 and 2000 from the lung, liver and intestine of two bearded dragons (Pogona vitticeps) and a chameleon (Chamaeleo quadricornis) and from the skin of a frill-necked lizard (Chamydosaurus kingii) by using viper heart cells (VH2) at 28 degrees C. Electron microscopic examination of infected VH2 cells revealed the assembly of icosahedral iridovirus-like particles measuring 139 nm (side to side) and 151 nm (apex to apex). Negatively stained virus particles had dimensions of 149 nm (side to side) and 170 nm (apex to apex). Polymerase chain reaction (PCR) amplification of purified viral DNA with primers corresponding to the partial gene encoding the major capsid protein (MCP) of Frog viris-3 (FV-3), the type species of the genus Ranavirus, was unsuccessful. In contrast, primers corresponding to the partial MCP gene of Chilo iridescent virus (CIV; genus Iridovirus) amplified 500-bp products with 97% identity to the nucleotide sequence of CIV and 100% identity to the nucleotide sequence of Gryllus bimaculatus iridescent virus (GbIV), an invertebrate iridescent virus. Virus protein profiles analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and restriction fragment length profiles of purified viral DNA treated with the endonucleases EcoRI, HindIII and HpaII were identical to those of GbIV.

Viruses of lower vertebrates

Viruses of lower vertebrates recently became a field of interest to the public due to increasing epizootics and economic losses of poikilothermic animals. These were reported worldwide from both wildlife and collections of aquatic poikilothermic animals. Several RNA and DNA viruses infecting fish, amphibians and reptiles have been studied intensively during the last 20 years. Many of these viruses induce diseases resulting in important economic losses of lower vertebrates, especially in fish aquaculture. In addition, some of the DNA viruses seem to be emerging pathogens involved in the worldwide decline in wildlife. Irido-, herpes- and polyomavirus infections may be involved in the reduction in the numbers of endangered amphibian and reptile species. In this context the knowledge of several important RNA viruses such as orthomyxo-, paramyxo-, rhabdo-, retro-, corona-, calici-, toga-, picorna-, noda-, reo- and birnaviruses, and DNA viruses such as parvo-, irido-, herpes-, adeno-, polyoma- and poxviruses, is described in this review.