Thomas Waltzek - Profile on Academia.edu (original) (raw)

Papers by Thomas Waltzek

Report of the Fifth International Symposium on Ranaviruses

Journal of herpetological medicine and surgery, Jan 25, 2021

1 Department of Natural Sciences, School of Nursing, Health, and Natural Sciences, Gordon State C... more 1 Department of Natural Sciences, School of Nursing, Health, and Natural Sciences, Gordon State College, 419 College Drive, Barnesville, GA 30204, USA 2 College of Public Health, Medical, and Veterinary Science, James Cook University, Townsville, Queensland, 4811, Australia 3 Department of Infectious Diseases and Immunology, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610, USA

Diverse eukaryotic dsDNA viruses, including adenoviruses, are thought to have evolved from bacter... more Diverse eukaryotic dsDNA viruses, including adenoviruses, are thought to have evolved from bacteriophages of the family Tectiviridae. The evolutionary relationship of the small circular dsDNA tumor viruses of the families Papillomaviridae and Polyomaviridae to other DNA virus families remains uncertain. Metagenomic surveys of fish reveal 5 previously unknown circular dsDNA viruses that could become founding members of a distinct viral family. These viruses encode predicted superfamily 3 helicases that are related to the replicative helicases of polyomaviruses and papillomaviruses. Additionally, the new viruses encode a gene cluster coding for homologs of adenovirus-like maturation proteases and putative homologs of adenovirus major and minor capsid proteins. We show that these predicted capsid protein are indeed incorporated into the adomavirus virions. Such combination of genes from unrelated virus families is unprecedented among known DNA viruses. We propose the name "Adomaviridae" for this emerging virus family.

Novel viral infections threatening Cyprinid fish

Bulletin of The European Association of Fish Pathologists, 2016

Diseases of Aquatic Organisms, Nov 22, 2016

Virus Research, Feb 1, 2020

Ecological Modelling, Oct 1, 2019

A consequence of genetic recombination can be the evolution of highly virulent pathogen strains. ... more A consequence of genetic recombination can be the evolution of highly virulent pathogen strains. Virulence can manifest through various mechanisms of host-pathogen interaction that facilitate transmission. We discovered a highly virulent chimeric ranavirus in Georgia, USA, estimated transmission parameters using controlled experiments, and developed compartmental disease models to examine potential consequences on tadpoles of a susceptible host species (Lithobates sylvaticus). Our models included three transmission pathways: direct transmission via host contact, environmental transmission via shed virions in water, and transmission via necrophagy of morbid individuals. Unlike previous models, we categorized individuals into multiple stages of infection (susceptible, latency, and infectious), where the probability of disease-induced mortality increased throughout the duration of infection following a gamma distribution with an integer shape parameter. Our simulations showed that accounting for pathogen incubation improved model predictions when compared to survival data from controlled experiments. We found that transmission due to direct contact of tadpoles was the dominant transmission pathway; however, environmental transmission played a larger role as tadpole density increased and the epidemic progressed. Estimated 0 (basic reproduction number) values > 570 for all transmission pathways indicate that targeting only one transmission pathway is unlikely to thwart invasion. Additionally, the high invasion potential and diseased-induced mortality associated with this chimeric ranavirus indicate that this pathogen is a substantial threat to amphibian biodiversity in the United States.

To investigate viral pathogens potentially involved in a mortality event of 21 Pacific harbor sea... more To investigate viral pathogens potentially involved in a mortality event of 21 Pacific harbor seals (Phoca vitulina richardsii) in California in 2000, viral metagenomics was performed directly on lung samples from five individuals. Metagenomics revealed a novel seal anellovirus (SealAV), which clusters phylogenetically with anelloviruses from California sea lions and domestic cats. Using specific PCR, SealAV was identified in lung tissue from two of five animals involved in the 2000 mortality event, as well as one of 20 harbor seal samples examined post-mortem in 2008. The identification of SealAV in multiple years demonstrates that this virus is persistent in the harbor seal population. SealAV is the second anellovirus reported in the lungs of pinnipeds, suggesting that anellovirus infections may be common amongst marine mammals and that more research is needed to understand the roles of these viruses in marine mammal health and disease.

Transboundary and Emerging Diseases

Infectious spleen and kidney necrosis virus (ISKNV) is a species within the genus Megalocytivirus... more Infectious spleen and kidney necrosis virus (ISKNV) is a species within the genus Megalocytivirus (family Iridoviridae), which causes high mortality disease in many freshwater and marine fish species. ISKNV was first reported in Asia and is an emerging threat to aquaculture with increasing global distribution, in part due to its presence in ornamental fish with clinical and subclinical infections. The species ISKNV includes three genotypes: red seabream iridovirus (RSIV), turbot reddish body iridovirus (TRBIV), and ISKNV. There is an increasing overlap in the recognized range of susceptible fish hosts and the geographic distribution of these distinct genotypes. To better understand the disease caused by ISKNV, a nucleic acid hybridization capture enrichment was used prior to sequencing to characterize whole genomes from archived clinical specimens of aquaculture and ornamental fish from Southeast Asia (n = 16). The method was suitable for tissue samples containing 2.50 × 104–4.58 × ...

PLOS ONE

Megalocytiviruses (MCVs) are double-stranded DNA viruses known to infect important freshwater and... more Megalocytiviruses (MCVs) are double-stranded DNA viruses known to infect important freshwater and marine fish species in the aquaculture, food, and ornamental fish industries worldwide. Infectious spleen and kidney necrosis virus (ISKNV) is the type species within the genus Megalocytivirus that causes red seabream iridoviral disease (RSIVD) which is a reportable disease to the World Animal Health Organization (WOAH). To better control the transboundary spread of this virus and support WOAH reporting requirements, we developed and partially validated a TaqMan real-time qPCR assay (ISKNV104R) to detect all three genotypes of ISKNV, including the two genotypes that cause RSIVD. Parameters averaged across 48 experiments used a 10-fold dilution series of linearized plasmid DNA (107–101 copies), carrying a fragment of the three-spot gourami iridovirus (TSGIV) hypothetical protein revealed that the assay was linear over 7 orders of magnitude (107–101), a mean efficiency of 99.97 ± 2.92%, a...

Diseases of Aquatic Organisms

Tilapia lake virus disease (TiLVD) is an emerging viral disease associated with high morbidity an... more Tilapia lake virus disease (TiLVD) is an emerging viral disease associated with high morbidity and mortality in cultured tilapia worldwide. In this study, we have developed and validated a TaqMan quantitative reverse transcription PCR (RT-qPCR) assay for TiLV, targeting a conserved region within segment 10 of the genome. The RT-qPCR assay was efficient (mean ± SD: 96.71 ± 3.20%), sensitive with a limit of detection of 10 RNA viral copies per reaction, and detected TiLV strains from different geographic regions including North America, South America, Africa, and Asia. The intra- and inter-assay variability ranged over 0.18-1.41% and 0.21-2.21%, respectively. The TaqMan RT-qPCR assay did not cross-react with other RNA viruses of fish, including an orthomyxovirus, a betanodavirus, a picornavirus, and a rhabdovirus. Analysis of 91 proven-positive and 185 proven-negative samples yielded a diagnostic sensitivity of 96.7% and a diagnostic specificity of 100%. The TaqMan RT-qPCR assay also ...

ARE PARTIAL MAJOR CAPSID PROTEIN AND eIF2-α SEQUENCES ENOUGH TO DETECT RECOMBINATION IN UK RANAVIRUS ISOLATES?

Georgia journal of science, 2018

Ranaviruses are emerging pathogens of ectothermic vertebrates around the globe. Recently, it has ... more Ranaviruses are emerging pathogens of ectothermic vertebrates around the globe. Recently, it has been discovered that recombination has played a role in the emergence of these pathogens in the Southeastern United States. Based on that, we hypothesized that the recombination was likely involved in the emergence of these pathogens in the United Kingdom. To test this hypothesis, we used partial sequences from BUK 2, BUK 3, and RUK 13, which were thought to be recombinant viruses based on previously published partial sequence analyses. However, when recombination analyses were performed using RDP4, no recombination was found in either the partial major capsid protein (MCP) gene or the putative eukaryotic initiation factor 2 - α (eIF2-α) homologue gene. This result was expected as the MCP of each of these isolates holds a 100% identity with the MCP of Frog virus 3 (Accession Number KJ175144.1), and the putative eIF2-α homologue holds 100% identity with the Chinese Giant Salamander Iridovirus (Accession Number KF512820.1), which was shown in previous studies. We believe that the short sequences used in this study (partial loci) are too short to show recombination and that full genome sequences are necessary to determine if recombination has occurred in the genomes of these virulent ranaviruses

Virology, Nov 10, 2017

Ranaviruses are emerging pathogens of fish, amphibians, and reptiles that threaten aquatic animal... more Ranaviruses are emerging pathogens of fish, amphibians, and reptiles that threaten aquatic animal industries and wildlife worldwide. Our objective was to genetically characterize ranaviruses isolated during separate bullfrog Lithobates catesbeianus die-offs that occurred eight years apart on the same North American farm. The earlier outbreak was due to a highly pathogenic strain of common midwife toad virus (CMTV) previously known only from Europe and China. The later outbreak was due to a chimeric ranavirus that displayed a novel genome arrangement and a DNA backbone typical for Frog virus 3 (FV3) strains except for interspersed fragments acquired through recombination with the CMTV isolated earlier. Both bullfrog ranaviruses are more pathogenic than wild-type FV3 suggesting recombination may have resulted in the increased pathogenicity observed in the ranavirus isolated in the later outbreak. Our study underscores the role international trade in farmed bullfrogs may have played in...

Diseases of Aquatic Organisms, 2016

Complete and transparent reporting of key elements of diagnostic accuracy studies for infectious ... more Complete and transparent reporting of key elements of diagnostic accuracy studies for infectious diseases in cultured and wild aquatic animals benefits end-users of these tests, enabling the rational design of surveillance programs, the assessment of test results from clinical cases and comparisons of diagnostic test performance. Based on deficiencies in the Standards for Reporting of Diagnostic Accuracy (STARD) guidelines identified in a prior finfish study , we adapted the Standards for Reporting of Animal Diagnostic Accuracy Studiesparatuberculosis (STRADAS-paraTB) checklist of 25 reporting items to increase their relevance to finfish, amphibians, molluscs, and crustaceans and provided examples and explanations for each item. The checklist, known as STRADAS-aquatic, was developed and refined by an expert group of 14 transdisciplinary scientists with experience in test evaluation studies using field and experimental samples, in operation of reference laboratories for aquatic animal pathogens, and in development of international aquatic animal health policy. The main changes to the STRADAS-paraTB checklist were to nomenclature related to the species, the addition of guidelines for experimental challenge studies, and the designation of some items as relevant only to experimental studies and ante-mortem tests. We believe that adoption of these guidelines will improve reporting of primary studies of test accuracy for aquatic animal diseases and facilitate assessment of their fitness-forpurpose. Given the importance of diagnostic tests to underpin the Sanitary and Phytosanitary agreement of the World Trade Organization, the principles outlined in this paper should be applied to other World Organisation for Animal Health (OIE)-relevant species.

PLoS ONE, 2014

Transmission is an essential process that contributes to the survival of pathogens. Ranaviruses a... more Transmission is an essential process that contributes to the survival of pathogens. Ranaviruses are known to infect different classes of lower vertebrates including amphibians, fishes and reptiles. Differences in the likelihood of infection among ectothermic vertebrate hosts could explain the successful yearlong persistence of ranaviruses in aquatic environments. The goal of this study was to determine if transmission of a Frog Virus 3 (FV3)-like ranavirus was possible among three species from different ectothermic vertebrate classes: Cope's gray treefrog (Hyla chrysoscelis) larvae, mosquito fish (Gambusia affinis), and red-eared slider (Trachemys scripta elegans). We housed individuals previously exposed to the FV3-like ranavirus with naı ¨ve (unexposed) individuals in containers divided by plastic mesh screen to permit water flow between subjects. Our results showed that infected gray treefrog larvae were capable of transmitting ranavirus to naı ¨ve larval conspecifics and turtles (60% and 30% infection, respectively), but not to fish. Also, infected turtles and fish transmitted ranavirus to 50% and 10% of the naı ¨ve gray treefrog larvae, respectively. Nearly all infected amphibians experienced mortality, whereas infected turtles and fish did not die. Our results demonstrate that ranavirus can be transmitted through water among ectothermic vertebrate classes, which has not been reported previously. Moreover, fish and reptiles might serve as reservoirs for ranavirus given their ability to live with subclinical infections. Subclinical infections of ranavirus in fish and aquatic turtles could contribute to the pathogen's persistence, especially when highly susceptible hosts like amphibians are absent as a result of seasonal fluctuations in relative abundance.

Antimicrobial Agents and Chemotherapy, 2003

Fluoroquinolone use in poultry production may select for resistant Escherichia coli that can be t... more Fluoroquinolone use in poultry production may select for resistant Escherichia coli that can be transmitted to humans. To define the prevalence and virulence potential of poultry-associated, quinolone-resistant E. coli in the United States, 169 retail chicken products from the Minneapolis-St. Paul area (1999 to 2000) were screened for nalidixic acid (Nal)-resistant E. coli . Sixty-two (37%) products yielded Nal-resistant E. coli . From 55 products that yielded both Nal-resistant and susceptible E. coli , two isolates (one resistant, one susceptible) per sample were further characterized. Twenty-three (21%) of the 110 E. coli isolates (13 resistant, 10 susceptible) satisfied criteria for extraintestinal pathogenic E. coli (ExPEC), i.e., exhibited ≥2 of pap (P fimbriae), sfa/foc (S/F1C fimbriae), afa/dra (Dr binding adhesins), iutA (aerobactin receptor), and kpsMT II (group 2 capsule synthesis). Compared with other isolates, ExPEC isolates more often derived from virulence-associated ...

Emerging Pathogens and a Current‐Use Pesticide: Potential Impacts on Eastern Hellbenders

Journal of Aquatic Animal Health

Populations of the eastern hellbender Cryptobranchus alleganiensis alleganiensis have been declin... more Populations of the eastern hellbender Cryptobranchus alleganiensis alleganiensis have been declining for decades, and emerging pathogens and pesticides are hypothesized to be contributing factors. However, few empirical studies have attempted to test the potential effects of these factors on hellbenders. We simultaneously exposed subadult hellbenders to environmentally relevant concentrations of either Batrachochytrium dendrobatidis (Bd) or a frog virus 3‐like ranavirus (RV), a combination of the pathogens, or each pathogen following exposure to a glyphosate herbicide (Roundup). Additionally, we measured the ability of the skin mucosome to inactivate Bd and RV in growth assays. We found that mucosome significantly inactivated RV by an average of 40% but had no negative effects on Bd growth. All treatments that included RV exposure experienced reduced survival compared to controls, and the combination of RV and herbicide resulted in 100% mortality. Histopathology verified RV as the c...

EDIS

Carp edema virus disease is killing wild and cultured varieties of carp and worrying koi enthusia... more Carp edema virus disease is killing wild and cultured varieties of carp and worrying koi enthusiasts and carp aquaculturists in the United States and around the world. The disease causes skin lesions and swelling and is sometimes called “koi sleepy disease” because infected fish become lethargic and unresponsive. This 6-page fact sheet describes symptoms, diagnosis, prevention, and what fish producers, wholesalers, or retailers can do if they suspect carp may have contracted the disease. Written by Shohreh Hesami, Pedro Viadanna, Natalie Steckler, Staci Spears, Patrick Thompson, Karen Kelley, Roy Yanong, Ruth Francis-Floyd, Johnny Shelley, Joseph Groff, Andy Goodwin, Olga Haenen, and Thomas Waltzek, and published by the School of Forest Resources and Conservation Program in Fisheries and Aquatic Sciences, October 2015. FA189/FA189: Carp Edema Virus Disease (CEVD) / Koi Sleepy Disease (KSD) (ufl.edu)

Journal of Molecular Evolution, 2007

Aromatase cytochrome P450 (P450arom), the enzyme that catalyzes estrogen synthesis, is required f... more Aromatase cytochrome P450 (P450arom), the enzyme that catalyzes estrogen synthesis, is required for successful reproduction and is encoded by a single copy gene (CYP19) in most mammals. However, pigs and their distant suiform relatives the peccaries experienced CYP19 duplication. Here, the evolutionary origin of CYP19 duplication, and the evolution of the gene paralogs, was explored further in collared peccaries (Pecari tayassu). Exons IV and V, and the intervening intron, representing duplicated CYP19 genes, were cloned and sequenced from collared peccary, pig, and hippopotamus. Sequence alignment and analysis identified a gene conversion in collared peccary with a breakpoint 102 base pairs (bp) upstream of exon V. Phylogenetic analyses of nucleotide and amino acid sequence upstream of the breakpoint supported a tree in which one peccary sequence was orthologous with the porcine gonadal gene. Cloning and sequencing of tissue transcripts, using reverse-transcriptase polymerase chain reaction techniques (RT-PCR), confirmed that the gonadal ortholog was expressed in collared peccary testis. Orthology of the other genomic sequence with the porcine placental gene was not resolved, but its placenta-specific expression in collared peccary was confirmed by similar transcript analysis. Immunoblot and enzyme activity in collared peccary testes demonstrated much lower levels of P450arom than in pig testis. Collared peccary placental P450arom expression also seemed much lower than pigs. Thus, suiform CYP19 genes arose from an ancestral duplication that has maintained gonad-and placenta-specific expression, but at lower levels in peccaries than pigs, perhaps facilitating the emergence of different reproductive strategies as Suiformes diverged and evolved.

The Journal of general virology, 2017

The Iridoviridae is a family of large, icosahedral viruses with double-stranded DNA genomes rangi... more The Iridoviridae is a family of large, icosahedral viruses with double-stranded DNA genomes ranging in size from 103 to 220 kbp. Members of the subfamily Alphairidovirinae infect ectothermic vertebrates (bony fish, amphibians and reptiles), whereas members of the subfamily Betairidovirinae mainly infect insects and crustaceans. Infections can be either covert or patent, and in vertebrates they can lead to high levels of mortality among commercially and ecologically important fish and amphibians. This is a summary of the current International Committee on Taxonomy of Viruses (ICTV) Report on the taxonomy of the Iridoviridae, which is available at www.ictv.global/report/iridoviridae.

Biology Letters, 2011

Emerging infectious diseases are a significant threat to global biodiversity. While historically ... more Emerging infectious diseases are a significant threat to global biodiversity. While historically overlooked, a group of iridoviruses in the genus Ranavirus has been responsible for die-offs in captive and wild amphibian, reptile and fish populations around the globe over the past two decades. In order to share contemporary information on ranaviruses and identify critical research directions, the First International Symposium on Ranaviruses was held in July 2011 in Minneapolis, MN, USA. Twenty-three scientists and veterinarians from nine countries examined the ecology and evolution of ranavirus–host interactions, potential reservoirs, transmission dynamics, as well as immunological and histopathological responses to infection. In addition, speakers discussed possible mechanisms for die-offs, and conservation strategies to control outbreaks.