Sequence comparison of the non-structural genes of four different types of Aleutian mink disease parvovirus indicates an unusual degree of variability

Prevalence of Aleutian Mink Disease Virus (AMDV) in Free-Ranging American Mink from Biebrza and Narew National Parks (Poland)-An Epidemiological Concern

Aleutian Mink Disease Virus (AMDV) is the causative agent of Aleutian disease (AD). This progressive and chronic disorder significantly impacts the mink breeding industry, affecting farmed and free-ranging American and European mink. This study investigated AMDV variants isolated from free-ranging American mink in northeastern Poland. Between 2018 and 2019, 26 spleen samples were collected from mink in Narew National Park (NNP) and Biebrza National Park (BNP). DNA was extracted and subjected to PCR to amplify the NS1 gene, followed by sequencing and phylogenetic analysis. The NS1 gene was detected in 50% of samples from NNP minks and in 30% of samples from BNP minks, with an overall prevalence of 42.31%; these findings align with global data and indicate serious ecological and health concerns. Ten closely related AMDV variants and one distinct variant were identified. The grouped variants exhibited high genetic homogeneity, closely related to strains found in mink from the USA, Germany, Greece, Latvia, and Poland; meanwhile, the distinct variant showed similarities to strains found in mink from Finland, Denmark, China, Poland, and Latvia, suggesting multiple infection sources. These findings, consistent with data from Polish mink farms, indicate significant genetic similarity between farmed and wild mink strains, suggesting potential bidirectional transmission. This underscores the importance of a One Health approach, emphasizing the interconnectedness of human, animal, and environmental health. Continuous surveillance and genetic studies are crucial for understanding AMDV dynamics and mitigating their impacts. Measures to reduce transmission between farmed and wild mink populations are vital for maintaining mink health and ecosystem stability.

Epidemiology, pathogenesis, and diagnosis of Aleutian disease caused by Aleutian mink disease virus: A literature review with a perspective of genomic breeding for disease control in American mink (Neogale vison)

Aleutian disease (AD) is a multi-systemic infectious disease in American mink (Neogale vison) caused by the Aleutian mink disease virus (AMDV). Commonly referred to as mink plasmacytosis, AD is an economically significant disease in mink-breeding countries. Aleutian disease mainly induces weight loss, lower fertility, and dropped pelt quality in adults and can result in acute interstitial pneumonia with high mortality rates in kits. In this review, we employed the scientific literature on AD over the last 70 years to discuss the historical and contemporary status of AD outbreaks and seroprevalence in mink farming countries. We also explained different forms of AD and the differences between the pathogenicity of the virus in kits and adults. The application of the available AD serological tests in AD control strategies was argued. We explained how selection programs could help AD control and proposed different approaches to selecting animals for building AD-tolerant herds. The advantages of genomic selection for AD tolerance over traditional breeding strategies were discussed in detail. We also explained how genomic selection could help AD control by selecting tolerant animals for the next generation based on genome-wide single nucleotide polymorphisms (SNP) data and the challenges of implementing genomic selection for AD tolerance in the mink industry. This review collected the information required for designing successful breeding programs for AD tolerance. Examples of the application of information are presented, and data gaps are highlighted. We showed that AD tolerance is necessary to be among the traits that animals are selected for in the mink industry.

Impact of viral features, host jumps and phylogeography on the rapid evolution of Aleutian mink disease virus (AMDV)

Aleutian mink disease virus (AMDV) is one the most relevant pathogens of domestic mink, where it can cause significant economic losses, and wild species, which are considered a threat to mink farms. Despite their relevance, many aspects of the origin, evolution, and geographic and host spreading patterns of AMDV have never been investigated on a global scale using a comprehensive biostatistical approach. The present study, benefitting from a large dataset of sequences collected worldwide and several phylodynamic-based approaches, demonstrates the ancient origin of AMDV and its broad, unconstrained circulation from the initial intercontinental spread to the massive among-country circulation, especially within Europe, combined with local persistence and evolution. Clear expansion of the viral population size occurred over time until more effective control measures started to be applied. The role of frequent changes in epidemiological niches, including different hosts, in driving the high nucleotide and amino acid evolutionary rates was also explored by comparing the strengths of selective pressures acting on different populations. The obtained results suggest that the viral passage among locations and between wild and domesticated animals poses a double threat to farm profitability and animal welfare and health, which is particularly relevant for endangered species. Therefore, further efforts must be made to limit viral circulation and to refine our knowledge of factors enhancing AMDV spread, particularly at the wild-domestic interface.

Molecular epidemiology of Aleutian mink disease virus from fecal swab of mink in northeast China

Background

Aleutian mink disease parvovirus (AMDV) causes Aleutian mink disease (AMD), which is a serious infectious disease of mink. The aim of this study was to get a better understanding of the molecular epidemiology of AMDV in northeast China to control and prevent AMD from further spreading. This study for the first time isolated AMDV from fecal swab samples of mink in China.

Results

A total of 157/291 (54.0%) of the fecal swab samples were positive for AMDV. Of these, 23 AMDV positive samples were randomly selected for sequence alignment and phylogenetic analysis based on the acquired partial fragments of VP2 gene with the hypervariable region. Comparative DNA sequence analysis of 23 AMDV isolates with a reference nonpathogenic (AMDV-G) strain revealed 8.3% difference in partial VP2 nucleotide sequences. Amino acid alignment indicated the presence of several genetic variants, as well as one single amino acid residue deletion. The most concentrated area of variation was located in the hypervariable region of VP2 protein. According to phylogenetic analysis, the Chinese AMDV strains and the other reference AMDV strains from different countries clustered into three groups (clades A, B and C). Most of the newly sequenced strains were found to form a Chinese-specific group, which solely consisted of Chinese AMDV strains.

Conclusion

These findings indicated that a high genetic diversity was found in Chinese AMDV strains and the virus distribution were not dependent on geographical origin. Both local and imported AMDV positive species were prevalent in the Chinese mink farming population. The genetic evidence of AMDV variety and epidemic isolates have importance in mink farming practice.

Endemic Skunk amdoparvovirus in free-ranging striped skunks (Mephitis mephitis) in California

The genus Amdoparvovirus includes the newly discovered skunk amdoparvovirus and the well-characterized Aleutian disease virus which causes significant health impacts in farmed mink worldwide. In 2010-2013, an outbreak of fatal amdoparvovirus-associated disease was documented in free-ranging striped skunks (Mephitis mephitis) from the San Francisco Bay Area of California. To characterize the geographic distribution, earliest occurrence and abundance of this virus, as well as possible impacts on sympatric mustelids of conservation concern, we tested blood samples from skunks throughout California and fishers (Pekania pennanti) from northern California for amdoparvovirus DNA. Amdoparvovirus DNA was detected in 64.8% of sampled skunks (140/216), and test-positive skunks were distributed widely throughout the state, from as far north as Humboldt County and south to San Diego County. The first test-positive skunks were detected from 2004, prior to the 2010-2013 outbreak. No significant spatial or temporal clustering of infection was detected. Although healthy and clinically ill animals tested positive for amdoparvovirus DNA, histopathologic evaluation of a subset from clinically ill skunks indicated that positive PCR results were associated with pneumonia as well as there being more than one inflammatory type lesion. None of 38 fishers were PCR-positive. Given the widespread geographic distribution and lack of a clear epizootic centre, our results suggest the presence of an endemic skunk-associated amdoparvovirus strain or species. However, if the virus is not host-specific, skunks' ubiquitous presence across rural and urban habitats may pose a risk to susceptible domestic and wild species including mustelids of conservation concern such as fishers and Pacific martens (Martes caurina).

Endogenous amdoparvovirus-related elements reveal insights into the biology and evolution of vertebrate parvoviruses

Amdoparvoviruses (family Parvoviridae: genus Amdoparvovirus) infect carnivores, and are a major cause of morbidity and mortality in farmed animals. In this study, we systematically screened animal genomes to identify endogenous parvoviral elements (EPVs) disclosing a high degree of similarity to amdoparvoviruses, and investigated their genomic, phylogenetic and protein structural features. We report the first examples of full-length, amdoparvovirus-derived EPVs in the genome of the Transcaucasian mole vole (Ellobius lutescens). We also identify four EPVs in mammal and reptile genomes that are intermediate between amdoparvoviruses and their sister genus (Protoparvovirus) in terms of their phylogenetic placement and genomic features. In particular, we identify a genome-length EPV in the genome of a pit viper (Protobothrops mucrosquamatus) that is more similar to a protoparvovirus than an amdoparvovirus in terms of its phylogenetic placement and the structural features of its capsid protein (as revealed by homology modeling), yet exhibits characteristically amdoparvovirus-like genome features including: (1) a putative middle ORF gene; (2) a capsid gene that lacks a phospholipase A2 domain; (3) a genome structure consistent with an amdoparvovirus-like mechanism of capsid gene expression. Our findings indicate that amdoparvovirus host range extends to rodents, and that parvovirus lineages possessing a mixture of proto- and amdoparvovirus-like characteristics have circulated in the past. In addition, we show that EPV sequences in the mole vole and pit viper encode intact, expressible replicase genes that have potentially been co-opted or exapted in these host species.

Construction and Immunogenicity Analysis of Whole-Gene Mutation DNA Vaccine of Aleutian Mink Virus Isolated Virulent Strain

Aleutian mink disease (AD) is a chronic viral infection that causes autoimmune disorders in minks and presents a significant economic burden on mink farming. Despite the substantial challenges presented by AD, no effective vaccine is available and only partial protection has been achieved. We constructed a whole-gene nucleic acid vaccine from an isolated virulent Aleutian mink disease virus (ADV) strain (pcDNA3.1-ADV). Based on this whole-gene nucleic acid vaccine, we generated truncated mutant constructs by removing portions of the ADV VP2 gene using overlap extension polymerase chain reaction. pcDNA3.1-ADV-428 lacks nucleotides encoding VP2 amino acid residues 428-466, and pcDNA3.1-ADV-428-487 harbors additional deletion of nucleotides coding for VP2 amino acid residues 487-501. We also generated nucleic acid vaccines for the ADV NS1 gene, truncated ADV NS1 gene, ADV VS2 gene, and truncated ADV VS2 gene: pcDNA3.1-NS1, pcDNA3.1-NS1-D, pcDNA3.1-VP2, and pcDNA3.1-VP2-D, respectively. The immunogenicity of the seven DNA vaccines was confirmed by immunofluorescent evaluation. Sixty female minks were divided into 10 groups: seven groups were immunized with the DNA vaccines, one control group was injected with phosphate-buffered saline, one group was immunized with pcDNA3.1 empty vector, and one group was immunized with inactivated ADV-G virus. ADV antibody levels, percentage of CD8⁺ cells in blood, and levels of γ-globulin and circulating immune complexes in the serum were evaluated longitudinally over 36 weeks after ADV challenge. Minks that were immunized with the pcDNA3.1-ADV-428-487 nucleic acid vaccine produced ADV antibodies. After ADV challenge, the minks immunized with pcDNA3.1-ADV-428-487 nucleic acid vaccine had lower γ-globulin content and lower CIC in serum compared to other immunization groups. Although the pcDNA3.1-ADV-428-487 nucleic acid vaccine did not demonstrate complete protection against ADV, it demonstrated marked efficacy and could potentially be used as a vaccine to prevent losses in mink populations due to ADV. Discovery of effective means to vaccinate mink against ADV will not only improve overall health of mink populations but will also reduce the economic impact of ADV.

Outbreak tracking of Aleutian mink disease virus (AMDV) using partial NS1 gene sequencing

Background

Aleutian Mink Disease (AMD) is an infectious disease of mink (Neovison vison) and globally a major cause of economic losses in mink farming. The disease is caused by Aleutian Mink Disease Virus (AMDV) that belongs to the genus Amdoparvovirus within the Parvoviridae family. Several strains have been described with varying virulence and the severity of infection also depends on the host’s genotype and immune status. Clinical signs include respiratory distress in kits and unthriftiness and low quality of the pelts. The infection can also be subclinical.

Systematic control of AMDV in Danish mink farms was voluntarily initiated in 1976. Over recent decades the disease was mainly restricted to the very northern part of the country (Northern Jutland), with only sporadic outbreaks outside this region. Most of the viruses from this region have remained very closely related at the nucleotide level for decades. However, in 2015, several outbreaks of AMDV occurred at mink farms throughout Denmark, and the sources of these outbreaks were not known.

Methods

Partial NS1 gene sequencing, phylogenetic analyses data were utilized along with epidemiological to determine the origin of the outbreaks.

Results

The phylogenetic analyses of partial NS1 gene sequences revealed that the outbreaks were caused by two different clusters of viruses that were clearly different from the strains found in Northern Jutland. These clusters had restricted geographical distribution, and the variation within the clusters was remarkably low. The outbreaks on Zealand were epidemiologically linked and a close sequence match was found to two virus sequences from Sweden. The other cluster of outbreaks restricted to Jutland and Funen were linked to three feed producers (FP) but secondary transmissions between farms in the same geographical area could not be excluded.

Conclusion

This study confirmed that partial NS1 sequencing can be used in outbreak tracking to determine major viral clusters of AMDV. Using this method, two new distinct AMDV clusters with low intra-cluster sequence diversity were identified, and epidemiological data helped to reveal possible ways of viral introduction into the affected herds.

Electronic supplementary material

The online version of this article (doi:10.1186/s12985-017-0786-5) contains supplementary material, which is available to authorized users.

Evolutionary analysis of whole-genome sequences confirms inter-farm transmission of Aleutian mink disease virus

Aleutian mink disease virus (AMDV) is a frequently encountered pathogen associated with mink farming. Previous phylogenetic analyses of AMDV have been based on shorter and more conserved parts of the genome, e.g. the partial NS1 gene. Such fragments are suitable for detection but are less useful for elucidating transmission pathways while sequencing entire viral genomes provides additional informative sites and often results in better-resolved phylogenies. We explore how whole-genome sequencing can benefit investigations of AMDV transmission by reconstructing the relationships between AMDV field samples from a Danish outbreak. We show that whole-genome phylogenies are much better resolved than those based on the partial NS1 gene sequences extracted from the same alignment. Well-resolved phylogenies contain more information about the underlying transmission trees and are useful for understanding the spread of a pathogen. In the main case investigated here, the transmission path suggested by the tree structure was supported by epidemiological data. The use of molecular clock models further improved tree resolution and provided time estimates for the viral ancestors consistent with the proposed direction of spread. It was however impossible to infer transmission pathways from the partial NS1 gene tree, since all samples from the case farms branched out from a single internal node. A sliding window analysis showed that there were no shorter genomic regions providing the same phylogenetic resolution as the entire genome. Altogether, these results suggest that phylogenetic analyses based on whole-genome sequencing taking into account sampling dates and epidemiological data is a promising set of tools for clarifying AMDV transmission.

A fast and robust method for whole genome sequencing of the Aleutian Mink Disease Virus (AMDV) genome

Aleutian Mink Disease Virus (AMDV) is a frequently encountered pathogen associated with commercial mink breeding. AMDV infection leads to increased mortality and compromised animal health and welfare. Currently little is known about the molecular evolution of the virus, and the few existing studies have focused on limited regions of the viral genome. This paper describes a robust, reliable, and fast protocol for amplification of the full AMDV genome using long-range PCR. The method was used to generate next generation sequencing data for the non-virulent cell-culture adapted AMDV-G strain as well as for the virulent AMDV-Utah strain. Comparisons at nucleotide- and amino acid level showed that, in agreement with existing literature, the highest variability between the two virus strains was found in the left open reading frame, which encodes the non-structural (NS1-3) genes. This paper also reports a number of differences that potentially can be linked to virulence and host range. To the authors' knowledge, this is the first study to apply next generation sequencing on the entire AMDV genome. The results from the study will facilitate the development of new diagnostic tools and can form the basis for more detailed molecular epidemiological analyses of the virus.

Genetic characterization of the complete genome of an Aleutian mink disease virus isolated in north China

The genome of a highly pathogenic strain of Aleutian disease mink virus (AMDV-BJ) isolated from a domestic farm in North China has been determined and compared with other strains. Alignment analysis of the major structural protein VP2 revealed that AMDV-BJ is unique among 17 other AMDV strains. Compared with the nonpathogenic strain ADV-G, the 3' end Y-shaped hairpin was highly conserved, while a 4-base deletion in the 5' U-shaped terminal palindrome resulted in a different unpaired "bubble" group near the NS1-binding region of the 5' end hairpin which may affect replication efficiency in vivo. We also performed a protein analysis of the NS1, NS2, and new-confirmed NS3 of AMDV-BJ with some related AMDV DNA sequence published, providing information on evolution of AMDV genes. This study shows a useful method to obtain the full-length genome of AMDV and some other parvoviruses.

Driving forces behind the evolution of the Aleutian mink disease parvovirus in the context of intensive farming

Aleutian mink disease virus (AMDV) causes plasmacytosis, an immune complex-associated syndrome that affects wild and farmed mink. The virus can also infect other small mammals (e.g., ferrets, skunks, ermines, and raccoons), but the disease in these hosts has been studied less. In 2007, a mink plasmacytosis outbreak began on the Island of Newfoundland, and the virus has been endemic in farms since then. In this study, we evaluated the molecular epidemiology of AMDV in farmed and wild animals of Newfoundland since before the beginning of the outbreak and investigated the epidemic in a global context by studying AMDV worldwide, thereby examining its diffusion and phylogeography. Furthermore, AMDV evolution was examined in the context of intensive farming, where host population dynamics strongly influence viral evolution. Partial NS1 sequences and several complete genomes were obtained from Newfoundland viruses and analyzed along with numerous sequences from other locations worldwide that were either obtained as part of this study or from public databases. We observed very high viral diversity within Newfoundland and within single farms, where high rates of co-infection, recombinant viruses and polymorphisms were observed within single infected individuals. Worldwide, we documented a partial geographic distribution of strains, where viruses from different countries co-exist within clades but form country-specific subclades. Finally, we observed the occurrence of recombination and the predominance of negative selection pressure on AMDV proteins. A surprisingly low number of immunoepitopic sites were under diversifying pressure, possibly because AMDV gains no benefit by escaping the immune response as viral entry into target cells is mediated through interactions with antibodies, which therefore contribute to cell infection. In conclusion, the high prevalence of AMDV in farms facilitates the establishment of co-infections that can favor the occurrence of recombination and enhance viral diversity. Viruses are then exchanged between different farms and countries and can be introduced into the wild, with the rapidly evolving viruses producing many parallel lineages.

Development of an Enzyme-Linked Immunosorbent Assay Based on Fusion VP2332-452 Antigen for Detecting Antibodies against Aleutian Mink Disease Virus

For detection of Aleutian mink disease virus (AMDV) antibodies, an enzyme-linked immunosorbent assay (ELISA) was developed using the recombinant VP2332-452 protein as an antigen. Counterimmunoelectrophoresis (CIEP) was used as a reference test to compare the results of the ELISA and Western blotting (WB); the specificity and sensitivity of the VP2332-452 ELISA were 97.9% and 97.3%, respectively, which were higher than those of WB. Therefore, this VP2332-452 ELISA may be a preferable method for detecting antibodies against AMDV.

Amdoparvoviruses in small mammals: expanding our understanding of parvovirus diversity, distribution, and pathology

Many new viruses have been discovered recently, thanks in part to the advent of next-generation sequencing technologies. Among the Parvoviridae, three novel members of the genus Amdoparvovirus have been described in the last 4 years, expanding this genus that had contained a single species since its discovery, Aleutian mink disease virus. The increasing number of molecular and epidemiological studies on these viruses around the world also highlights the growing interest in this genus. Some aspects of amdoparvoviruses have been well characterized, however, many other aspects still need to be elucidated and the most recent reviews on this topic are outdated. We provide here an up-to-date overview of what is known and what still needs to be investigated about these scientifically and clinically relevant animal viruses.

Molecular characterization of the small nonstructural proteins of parvovirus Aleutian mink disease virus (AMDV) during infection

Aleutian mink disease virus (AMDV) is the only member in genus Amdovirus of the family Parvoviridae. During AMDV infection, six species of viral transcripts are generated from one precursor mRNA through alternative splicing and alternative polyadenylation. In addition to the large non-structural protein NS1, two small non-structural proteins, NS2 and NS3, are putatively encoded (Qiu J, et al., 2006. J. Virol. 80 654-662). However, these two proteins have not been experimentally demonstrated during virus infection, and nothing is known about their function. Here, we studied the nonstructural protein expression profile of AMDV, and for the first time, confirmed expression of NS2 and NS3 during infection, and identified their intracellular localization. More importantly, we provided evidence that both NS2 and NS3 are necessary for AMDV replication.

Molecular epidemiology of Aleutian disease virus in free-ranging domestic, hybrid, and wild mink

Aleutian mink disease (AMD) is a prominent infectious disease in mink farms. The AMD virus (AMDV) has been well characterized in Europe where American mink (Neovison vison) are an introduced species; however, in North America, where American mink are native and the disease is thought to have originated, the virus’ molecular epidemiology is unknown. As such, we characterized viral isolates from Ontario free-ranging mink of domestic, hybrid, and wild origin at two proteins: NS1, a nonstructural protein, and VP2, a capsid protein. AMDV DNA was detected in 25% of free-ranging mink (45 of 183), indicating prevalent active infection. Median-joining networks showed that Ontario AMDV isolates formed two subgroups in the NS1 region and three in the VP2 region, which were somewhat separate from, but closely related to, AMDVs circulating in domestic mink worldwide. Molecular analyses showed evidence of AMDV crossing from domestic to wild mink. Our results suggest that AMDV isolate grouping is linked to both wild endogenous reservoirs and the long-term global trade in domestic mink, and that AMD spills back and forth between domestic and wild mink. As such, biosecurity on mink farms is warranted to prevent transmission of the disease between mink farms and the wild.

Genetic characterization of Aleutian mink disease viruses isolated in China

Aleutian mink disease virus (AMDV) is a parvovirus that causes an immune complex mediated disease in minks. To understand the genetic characterization of AMDV in China, the genomic sequences of three isolates, ADV-LN1, ADV-LN2, and ADV-LN3, from different farms in the Northern China were analyzed. The results showed that the lengths of genomic sequences of three isolates were 4,543, 4,566, and 4,566 bp, respectively. They shared only 95.5-96.3 % nucleotide identity with each other. The nucleotide and amino acid homology of genome sequence between the Chinese isolates and European or American strains (ADV-G, ADV-Utah1, and ADV-SL3) were 92.4-95.0 % and 92.1-93.8 %, respectively. The amino acid substitutions randomly distributed in the genome, especially NS gene. ADV-LN1 strain had a 9-amino-acid deletion at amino acid positions 70 and 72-79 in the VP1 gene, comparing with ADV-G strain; ADV-LN2 and ADV-LN3 strains had 1-amino-acid deletion at amino acid positions 70 in the VP1. Some potential glycosylation site mutations in VP and NS genes were also observed. Phylogenetic analysis results showed that the three strains belonged to two different branches based on the complete coding sequence of VP2 gene. However, they all were in the same group together with the strains from United States based on the NS1 sequence. It indicated that Chinese AMDV isolates had genetic diversity. The origin of the ancestors of the Chinese AMDV strains might be associated with the American strains.

Phylogenetic analysis of the VP2 gene of Aleutian mink disease parvoviruses isolated from 2009 to 2011 in China

Aleutian mink disease parvovirus (AMDV) is a non-enveloped virus with a single-stranded DNA genome that causes a fatal, usually persistent immune complex disease in minks. In this study, a total of 18,654 serum samples were collected from minks that were farmed in China from 2009 to 2011. After testing by counter-current immunoelectrophoresis (CIE), the seroprevalence of AMDV was found to be 68.67 %. The results show that there is a serious epidemic among Chinese minks used for breeding. To gain detailed information regarding the molecular epidemiology of AMDV in China, nine strains of AMDV were isolated from mink samples that were collected from four of the primary mink farming areas in China. The full-length capsid protein VP2 gene from each strain was sequenced after PCR amplification, and a phylogenetic analysis was performed on the VP2 gene sequence, including the VP2 genes from the other 10 AMDV strains available in the GenBank database, which were submitted from the 1970s to 2009. The phylogenetic analysis showed that the AMDV isolates were divided into five independent clades. The Chinese AMDV strains were distributed among all five groups and showed a high level of genetic diversity. Over 50 % of the Chinese AMDV strains were classified into two clades that consisted only of isolates from China and that were distinct from AMDV strains found in other countries. This finding indicated that both local and imported ADMV species are prevalent in the Chinese mink farming population.

Diversity and stability of Aleutian mink disease virus during bottleneck transitions resulting from eradication in domestic mink in Denmark

Aleutian mink disease (plasmacytosis) virus (AMDV) in domestic mink (Neovison vison) has been subject to eradication in Denmark since 1976. In 2001, approximately 5% of Danish mink farms were still infected and all were located in the northern part of the peninsula of Jutland. In the present study a total of 274 Danish isolates of AMDV collected during the two seasons of 2004 and 2005 were characterized by partial sequencing of the coding region of the non-structural (NS) proteins. Older AMDV isolates from Denmark, available, were also included. The Danish isolates represent a very homogenous cluster compared with Swedish, Finnish and Dutch isolates and seem to represent a minor fraction of the genetic diversity previously found in Denmark. Stability of nucleotide deviations reveals that the purifying selection of bottlenecks imposed on the AMDV population in Denmark by the stamping out policy for more than 6 years exceeds the rate of mutation driven diversity. Among the isolates from farms in northern Jutland two distinct types could be identified and within each of them a number of sub-types which were all useful in tracking spread of infections. Infection at a farm the preceding season was a predisposing risk parameter for disease outbreak at a farm, and strain identity substantiates the suggestion that inadequate disinfection is involved in the recurrence of outbreaks. In cases of new introductions to farms it is indicated that contact including transport between farms played a most significant role.

Implementation and validation of a sensitive PCR detection method in the eradication campaign against Aleutian mink disease virus

Aleutian mink disease virus (AMDV) is a severe progressive disease causing multiple different clinical syndromes in mink. In Denmark, the disease is notifiable and under official control. The control programme, based on serological screening, has confined successfully AMDV to the northern part of Denmark. However, re-infections and new introductions of virus into farms require a confirmatory virological test to verify the positive test results of single animals and ultimately to investigate disease transmission. A one step PCR amplifying a 374-base fragment of the NS1 gene of AMDV was compared to the counter-current immune electrophoresis (CIE) routinely used in the serological screening programme. Mink organs (n=299) obtained from 55 recently infected farms and 8 non-infected farms from 2008 to 2010 were tested by PCR, and the results were found to have a high correlation with the serological status of the mink. The relative diagnostic sensitivity of the PCR was 94.7%, and the relative diagnostic specificity was 97.9% when read in parallel with the CIE. PCR positive samples were sequenced and phylogenetic analysis revealed high similarity within the analysed AMDV strains and to AMDV strains described previously.

Development and evaluation of an enzyme-linked immunosorbent assay based on recombinant VP2 capsids for the detection of antibodies to Aleutian mink disease virus

Aleutian disease (AD), a common infectious disease in farmed minks worldwide, is caused by Aleutian mink disease virus (AMDV). Serodiagnosis of AD in minks has been based on detection of AMDV antibodies by counterimmunoelectrophoresis (CIE) since the 1980s. The aim of this study was to develop and evaluate an enzyme-linked immunosorbent assay (ELISA) based on recombinant virus-like particles (VLPs) for identifying AMDV antibodies from mink sera. AMDV capsid protein (VP2) of a Finnish wild-type strain was expressed by the baculovirus system in Spodoptera frugiperda 9 insect cells and was shown to self-assemble to VLPs (with an ultrastructure similar to that of the actual virion). A direct immunoglobulin G ELISA was established using purified recombinant AMDV VP2 VLPs as an antigen. Sera from farmed minks were collected to evaluate the AMDV VP2 ELISA (n = 316) and CIE (n = 209) based on AMDV VP2 recombinant antigen in parallel with CIE performed using a commercially available traditional antigen. CIE performed with the recombinant antigen had a sensitivity and specificity of 100% and ELISA a sensitivity of 99% and a specificity of 97%, with reference to CIE performed with the commercial antigen. The results show that the recombinant AMDV VP2 VLPs are antigenic and that AMDV VP2 ELISA is sensitive and specific and encourage further development of the method for high-throughput diagnostics, involving hundreds of thousands of samples in Finland annually.

Molecular epidemiology of Aleutian mink disease virus in Finland

Aleutian mink disease virus (AMDV) is a parvovirus that causes an immune complex-mediated disease in minks. To gain a more detailed view of the molecular epidemiology of mink AMDV in Finland, we phylogenetically analysed 14 new Finnish strains from 5 farms and all 40 strains with corresponding sequences available in GenBank. A part of the major non-structural (NS1) protein gene was amplified and analysed phylogenetically. A rooted nucleotide tree was constructed using the maximum parsimony method. The strains described in this study showed 86-100% nucleotide identity and were nearly identical on each farm. The ratio of synonymous to non-synonymous substitutions was approximately 2.7, indicating a mild purifying selection. Phylogenetic analysis confirmed that AMDV strains form three groups (I-III), all of which contained Finnish strains. The tree inferred that the three lineages of AMDV have been introduced to Finland independently. The analysis suggested that AMDV strains do not cluster into genotypes based on geographical origin, year of isolation or pathogenicity. Based on these data, the molecular clock is not applicable to AMDV, and within this gene area no recombination was detected.

Comparative analysis reveals frequent recombination in the parvoviruses

Parvoviruses are small single-stranded DNA viruses that are ubiquitous in nature. Infections with both autonomous and helper-virus dependent parvoviruses are common in both human and animal populations, and many animals are host to a number of different parvoviral species. Despite the epidemiological importance of parvoviruses, the presence and role of genome recombination within or among parvoviral species has not been well characterized. Here we show that natural recombination may be widespread in these viruses. Different genome regions of both porcine parvoviruses and Aleutian mink disease viruses have conflicting phylogenetic histories, providing evidence for recombination within each of these two species. Further, the rodent parvoviruses show complex evolutionary histories for separate genomic regions, suggesting recombination at the interspecies level.

High genetic diversity of the VP2 gene of a canine parvovirus strain detected in a domestic cat

This study reports the detection of co-infection by multiple CPV variants and the high genetic complexity of a CPV-2 strain detected in a domestic cat. The CPV variants selected by cloning the VP2 gene were sequenced, and genetic diversity and selection pressure were investigated. Comparison of the nucleotide sequences has evidenced 10 different viral populations, and, in the same animal, more CPV variants coexist. Our analysis excludes the possibility that the recombination events took place during infection and that negative selection acted on the VP2 gene. These findings confirm that CPV-2 shows high genetic heterogeneity resembling the quasispecies found in RNA viruses.

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.

DNA vaccination with the Aleutian mink disease virus NS1 gene confers partial protection against disease

Aleutian disease virus (ADV) causes severe losses in mink. This happens in nature as well as in farms. In spite of several attempts to provide an efficient protective protein based vaccine, experiments have failed so far. Only partial protection has been obtained. The aim of this work was to construct and test a protective DNA vaccine based on the gene encoding for the ADV non-structural protein 1 (NS1) and to test this construct as a potential vaccine candidate against ADV infection or disease. First, the vaccine construct was tested by in vitro transfection studies. NS1 protein expression was found by immunofluorescent studies and the expected size of translated protein confirmed by Western blot. Then, 18 female mink were divided into three groups: a control group, a DNA vaccinated group, and a group which received DNA vaccine plus a boost with recombinant NS1 protein in the last immunization. After virus challenge, the two DNA vaccinated groups induced higher antibody levels in the first 23 weeks of the 32 week observation period. One month after virus challenge, the most interesting finding was, that the "DNA+protein" group exhibited a significantly higher percentage of CD8+ cells, when compared to the levels in the two other groups. This, we believe, indicate a memory CTL response created by the vaccination. Most CD8+ cells were found to contain interferon gamma as measured by FACS intracellular staining. Severity of Aleutian disease was judged by quantification of plasma gammaglobulin levels and mink death statistics. The findings let us to conclude, that the two DNA vaccinated groups of mink did show milder disease characteristics, but that the vaccine effect also in this trial could only be characterized as partial.

Caspase cleavage of the nonstructural protein NS1 mediates replication of Aleutian mink disease parvovirus

Virus-induced apoptosis of infected cells can limit both the time and the cellular machinery available for virus replication. Hence, many viruses have evolved strategies to specifically inhibit apoptosis. However, Aleutian mink disease parvovirus (ADV) is the first example of a DNA virus that not only induces apoptosis but also utilizes caspase activity to facilitate virus replication. To determine the function of caspase activity during ADV replication, virus-infected cell lysates or purified ADV proteins were incubated with various purified caspases. Caspases cleaved the major nonstructural protein of ADV (NS1) at two caspase recognition sequences, whereas ADV structural proteins could not be cleaved. Importantly, the NS1 products could be identified in ADV-infected cells but were not present in infected cells pretreated with caspase inhibitors. By mutating putative caspase cleavage sites (D to E), we mapped the two cleavage sites to amino acid residues NS1:227 (INTD downward arrow S) and NS1:285 (DQTD downward arrow S). Replication of ADV containing either of these mutations was reduced 10(3)- to 10(4)-fold compared to that of wild-type virus, and a construct containing both mutations was replication defective. Immunofluorescent studies revealed that cleavage was required for nuclear localization of NS1. The requirement for caspase activity during permissive replication suggests that limitation of caspase activation and apoptosis in vivo may be a novel approach to restricting virus replication.

Effect of a valine residue at codon 352 of the VP2 capsid protein on in vivo replication and pathogenesis of Aleutian disease parvovirus in mink

OBJECTIVE

To determine whether a group of 3 genetic differences in the nonstructural protein (NS1) or 1 genetic difference in the structural protein (VP2) of Aleutian disease parvovirus (ADV) is responsible for an increase in the in vivo replication and pathogenicity of G/U-8, a chimera of ADV-G (nonpathogenic) and ADV-Utah (pathogenic), compared with G/U-10.

ANIMALS

32 eight-month-old female sapphire mink (Mustela vison).

PROCEDURE

Chimeric viruses were constructed, propagated in vitro, and used to inoculate mink. Antiviral antibody responses, presence of serum viral nucleic acid, and serum gamma globulin concentrations were monitored for 120 days following inoculation. Histologic examination of the liver, kidneys, spleen, and mesenteric lymph nodes was performed after necropsy.

RESULTS

A chimera containing only the 3 amino acid substitutions in NS1 did not elicit measurable responses indicative of replication or pathogenicity in inoculated mink. Serum antiviral antibody responses, frequency of detection of viral nucleic acid in serum, gamma globulin response, and histologic changes in mink inoculated with chimeras containing a valine residue at codon 352 (352V) of VP2 capsid were increased, compared with values from mink inoculated with chimeric viruses that did not contain 352V.

CONCLUSIONS AND CLINICAL RELEVANCE

A valine residue at codon 352 in the VP2 capsid protein of ADV affects in vivo viral replication and pathogenicity. This amino acid may be part of an incompletely defined pathogenic determinant of ADV. Further characterization of the pathogenic determinant may allow future development of focused preventive and therapeutic interventions for Aleutian disease of mink.

Nucleotide sequence and polymerase chain reaction/restriction fragment length polymorphism analyses of Aleutian disease virus in ferrets in Japan

Two ferrets with spontaneous Aleutian disease (AD) were found in Japan. The diagnosis was verified by polymerase chain reaction (PCR) amplification of part of the capsid gene specific to AD virus (ADV). The nucleotide sequences (365 bp in length) of the amplified fragments from the 2 ferrets differed by a single nucleotide, producing an amino acid alteration. Compared with other types of ADV, these isolates had 96% sequence similarity to a published ferret ADV (FADV) in contrast to <91% homology to various types of mink ADV (MADV). The phylogenetic tree of ADVs indicates that these 2 isolates and the published FADV belong to the same genetic group and definitely are divergent from MADVs. The predicted amino acid sequence of the hypervariable segment in the capsid gene was conserved among the 3 types of FADV. These results indicated that the 2 isolates found in Japan were new DNA types of FADV and could have been derived from FADV(s). A restriction fragment length polymorphism (RFLP) method to distinguish the ferret types of ADV from the mink types of ADV was developed on the basis of differences in their nucleotide sequences. Digestion of the PCR products with Afal or ScaI provided different cleavage patterns for FADV and MADV. This PCR/RFLP analysis of the ADV capsid gene will be a valuable asset for diagnosis of this virus infection in ferrets.

Unusual, high genetic diversity of Aleutian mink disease virus

The genetic diversity of Aleutian mink disease virus (AMDV) was examined. Sequences obtained from 35 clinical samples were compared with five published sequences. An unusual, high genetic variability was revealed. Three phylogenetic subgroups of AMDV were identified, and the presence of more than one genotype at some farms was detected.

Epitope mapping of Aleutian mink disease parvovirus virion protein VP1 and 2

Six overlapping fragments of the Aleutian Mink Disease parvoVirus (AMDV) virion protein VP1 and 2 (VP1/2) gene were inserted into the expression vector pMAL-c2. Four of the clones carried large overlapping fragments covering the entire VP1/2 gene. The remaining two clones covered specifically chosen regions within the VP1/2 gene. Using a Western blotting detection system, sera from AMDV-infected mink were tested against the recombinant polypeptides. These studies showed reactions primarily directed against the two AMDV polypeptides ranging from amino acids 297 to 518. Weaker reactions against other regions of the VP1/2 were also observed. The small fusion protein designed to cover the presumed AMDV VP1/2 loop 4 was purified by affinity chromatography and used to develop solid-phase immunoassays. Twelve small synthetic peptides were constructed and used as inhibitors. A peptide covering amino acids S428 to T448 was shown to block the reactivity of a pool of positive mink sera, indicating the presence of one dominant linear epitope.

Construction of pathogenic molecular clones of Aleutian mink disease parvovirus that replicate both in vivo and in vitro

The ADV-G isolate of Aleutian mink disease parvovirus (ADV) replicates permissively in Crandell feline kidney (CRFK) cells but is nonpathogenic for mink, whereas the highly pathogenic ADV-Utah isolate is nonviable in CRFK cells. To assign control of host range in CRFK cells and pathogenicity to specific regions of the ADV genome, we constructed a full-length molecular clone chimeric between ADV-G and ADV-Utah. If either the map unit (MU) 54-65 (clone G/U-5) or MU 65-88 (clone G/U-7) sections were ADV-Utah, viability in CRFK cells was abolished, thus indicating that in vitro host range was controlled by two independent determinants: A in the MU 54-65 segment and B in the MU 65-88 segment. Determinant B could be divided into two subregions, B1 (MU 65-69) and B2 (MU 73-88), neither of which alone could inhibit replication in CRFK cells, an observation suggesting that expression of the B determinant required interaction between noncontiguous sequences. Adult mink of Aleutian genotype inoculated with G/U-8 or G/U-10 developed viremia, antiviral antibody, and histopathological changes characteristic of progressive Aleutian disease. The capsid sequences of G/U-8 and G/U-10 differed from ADV-G at five and four amino acid residues, respectively. Our results suggested that the host range and pathogenicity of ADV are regulated by sequences in the capsid protein gene.

Vaccination with Aleutian mink disease parvovirus (AMDV) capsid proteins enhances disease, while vaccination with the major non-structural AMDV protein causes partial protection from disease

Vaccination studies were performed with partially purified recombinant AMDV VP1/2 capsids as well as with the major AMDV non-structural protein (NS1). All vaccine constructs induced an antibody response, but did not prevent infection upon challenge with AMDV. The severity of Aleutian disease (AD) was judged by the serum gammaglobulin level, the quantity of peripheral blood CD8 lymphocytes, antibody titers to VP1/2 and NS1 proteins and mink death rates. The VP1/2 vaccine constructs enhanced the disease process with drastic death rates for the vaccinated mink. On the contrary, the NS1 vaccine constructs resulted in milder AD than seen in the non-vaccinated mink.

Analyses of leucocytes in blood and lymphoid tissues from mink infected with Aleutian mink disease parvovirus (AMDV)

Mink were infected with Aleutian Mink Disease Parvovirus (AMDV) and sacrificed at monthly intervals after infection. During this time humoral immune responses and leucocyte numbers in blood, mesenteric lymph node, spleen and thymus were monitored. Serum hypergammaglobulinaemia was observed together with elevated antibody responses to AMDV NS1 and VP1/2 proteins. In blood, a highly significant increase in CD8+ lymphocytes was observed. However, (presumed)CD4+ cells defined as CD3+CD8- cells, and B lymphocytes remained relatively constant throughout the study. The (presumed)CD4+/CD8+ ratio decreased significantly from greater than 2 to less than 0.5 and MHC-II+ blood leucocytes increased significantly during infection, a large proportion of these being CD8+. Similar changes were observed in the mesenteric lymph node and spleen. Immunohistology of lymph nodes showed a massive expansion of the paracortical area due to increased numbers of CD8+ cells. The staining intensity of B lymphocytes in lymph nodes with a CD79a reactive monoclonal antibody was decreased in the late infection, indicating a possible greater number of plasma cells. Thymic involution was observed during the AMDV infection, although relative increases in CD3high (presumed)CD4+ and CD3highCD8+ single positive cells were observed. These increases were countered by a corresponding reduction in the CD3low(presumed)CD4+CD8+ double positive cell population. Immunohistology of the thymus in normal mink showed that most of the matured CD3+ T cells were present in the inner medulla, while only few CD3+ cells could be found in the outer cortex. In severely infected mink the thymic structural organisation vanished, and CD3+ cells were found throughout the organ.

Two parvoviruses that cause different diseases in mink have different transcription patterns: transcription analysis of mink enteritis virus and Aleutian mink disease parvovirus in the same cell line

The two parvoviruses of mink cause very different diseases. Mink enteritis virus (MEV) is associated with rapid, high-level viral replication and acute disease. In contrast, infection with Aleutian mink disease parvovirus (ADV) is associated with persistent, low-level viral replication and chronic severe immune dysregulation. In the present report, we have compared viral transcription in synchronized CRFK cells infected with either MEV or ADV using a nonradioactive RNase protection assay. The overall level of viral transcription was 20-fold higher in MEV- than in ADV-infected cells. Furthermore, MEV mRNA encoding structural proteins (MEV mRNA R3) was dominant throughout the infectious cycle, comprising approximately 80% of the total viral transcription products. In marked contrast, in ADV-infected cells, transcripts encoding nonstructural proteins (ADV mRNA R1 and R2) comprised more than 84% of the total transcripts at all times after infection, whereas ADV mRNA R3 comprised less than 16%. Thus, the ADV mRNA coding for structural proteins (ADV mRNA R3) was present at a level at least 100-fold lower than the corresponding MEV mRNA R3. These findings paralleled previous biochemical studies analyzing in vitro activities of the ADV and MEV promoters (J. Christensen, T. Storgaard, B. Viuff, B. Aasted, and S. Alexandersen, J. Virol. 67:1877-1886, 1993). The overall low levels of ADV mRNA and the paucity of the mRNA coding for ADV structural proteins may reflect an adaptation of the virus for low-level restricted infection.

The relationship between capsid protein (VP2) sequence and pathogenicity of Aleutian mink disease parvovirus (ADV): a possible role for raccoons in the transmission of ADV infections

Aleutian mink disease parvovirus (ADV) DNA was identified by PCR in samples from mink and raccoons on commercial ranches during an outbreak of Aleutian disease (AD). Comparison of DNA sequences of the hypervariable portion of VP2, the major capsid protein of ADV, indicated that both mink and raccoons were infected by a new isolate of ADV, designated ADV-TR. Because the capsid proteins of other parvoviruses play a prominent role in the determination of viral pathogenicity and host range, we decided to examine the relationship between the capsid protein sequences and pathogenicity of ADV. Comparison of the ADV-TR hypervariable region sequence with sequences of other isolates of ADV revealed that ADV-TR was 94 to 100% related to the nonpathogenic type 1 ADV-G at both the DNA and amino acid levels but less than 90% related to other pathogenic ADVs like the type 2 ADV-Utah, the type 3 ADV-ZK8, or ADV-Pullman. This finding indicated that a virus with a type 1 hypervariable region could be pathogenic. To perform a more comprehensive analysis, the complete VP2 sequence of ADV-TR was obtained and compared with that of the 647-amino-acid VP2 of ADV-G and the corresponding VP2 sequences of the pathogenic ADV-Utah, ADV-Pullman, and ADV-ZK8. Although the hypervariable region amino acid sequence of ADV-TR was identical to that of ADV-G, there were 12 amino acid differences between ADV-G and ADV-TR. Each of these differences was at a position where other pathogenic isolates also differed from ADV-G. Thus, although ADV-TR had the hypervariable sequence of the nonpathogenic type 1 ADV-G, the remainder of the VP2 sequence resembled sequences of other pathogenic ADVs. Under experimental conditions, ADV-TR and ADV-Utah were highly pathogenic and induced typical AD in trios of both Aleutian and non-Aleutian mink, whereas ADV-Pullman was pathogenic only for Aleutian mink and ADV-G was noninfectious. Trios of raccoons experimentally inoculated with ADV-TR and ADV-Utah all became infected with ADV, but only a single ADV-Pullman-inoculated raccoon showed evidence of infection. Furthermore, none of the ADV isolates induced pathological findings of AD in raccoons. Finally, when a preparation of ADV-TR prepared from infected raccoon lymph nodes was inoculated into mink and raccoons, typical AD was induced in Aleutian and non-Aleutian mink, but raccoons failed to show serological or pathological evidence of infection. These results indicated that raccoons can become infected with ADV and may have a role in the transmission of virus to mink but that raccoon-to-raccoon transmission of ADV is unlikely.