Serological analyses of different mink Aleutian disease virus strains

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.

Identification of a DNA segment in ferret Aleutian disease virus similar to a hypervariable capsid region of mink Aleutian disease parvovirus

A 401bp DNA fragment of ferret Aleutian disease virus (ADV) was amplified using PCR primers spanning a hypervariable region of mink ADV capsid sequence. The amplified fragment was 88-89% homologous to the same region of previously known sequence of three different strains of mink ADV, however, as low as 54% homology was observed when compared with a 39bp segment known as hypervariable region. Within the predicted 13 amino acid hypervariable region, the ferret ADV sequence differed at 6 positions from the wild type mink Utah1 strain. Three amino acids Gln289, Glu293 and Thr295 in this region were common to the pathogenic ferret ADV, mink Utah1 and ADVK strains, but differed from the cell culture adapted nonpathogenic mink strain ADVG suggesting that these three conserved residues may have some functional significance.

Acute interstitial pneumonia in mink kits inoculated with defined isolates of Aleutian mink disease parvovirus

The present study addressed the causal role of Aleutian mink disease parvovirus (ADV) in acute interstitial pneumonia in mink kits. All the examined isolates of ADV caused interstitial pneumonia in newborn kits, although the severity of disease and the mortality varied. These findings indicate that ADV is the direct causal agent of this disease in mink kits and that cofactors, which could have been present in the original ADV-K isolate, do not play a role. Acute interstitial pneumonia characterized by hypertrophy and hyperplasia of alveolar type II cells, intranuclear viral inclusions, interstitial edema, and hyaline membrane formation was experimentally reproduced in mink kits infected as newborns with five different isolates of ADV. Four hundred forty-nine newborn mink kits were included in the study, of which 247 were necropsied. The lesions caused by the different isolates were indistinguishable by histopathologic examination, but the incidence (50-100%) and severity (mortality of 30-100%, n = 218) of disease among the mink kits varied. Also, the content of ADV antigens in the lungs of infected kits varied among the groups. According to these features, the examined isolates could be placed in groups of high and low virulence. ADV-K, ADV-Utah I, and ADV-DK were in a highly virulent group producing a mortality of 90-100% (n = 110) in mink inoculated as newborns. ADV-GL and ADV-Pullman belonged to a group of low virulence, with an incidence of clinical disease of 50-70% and a mortality of approximately 30-50% (n = 118) in kits inoculated as newborns. The mortality in the control group receiving a mock inoculum was around 12% (n = 34). The period from infection to development of fatal disease varied from approximately 12 days for the highly virulent isolates up to around 20 days for the isolates of low virulence. The 107 mink kits that survived inoculation with ADV as newborns developed lesions typical of classical Aleutian disease irrespective of the ADV isolate used. The lesions consisted of chronic immune complex-mediated glomerulonephritis and infiltrations with mononuclear cells, including plasma cells in lung, liver, spleen, kidney, mesenteric lymph node, and intestine. Surviving kits also had hypertrophy of the bronchus-associated lymphoid tissue and focal subpleural, intraalveolar accumulations of large cells with foamy cytoplasm, so-called lipid pneumonia.

Evidence of restricted viral replication in adult mink infected with Aleutian disease of mink parvovirus

Strand-specific hybridization probes were used in in situ molecular hybridization specifically to localize cells containing replicative intermediates of Aleutian disease of mink parvovirus (ADV). When adult mink of Aleutian genotype were infected with ADV Utah I, the largest number of cells positive for viral replication (i.e., containing replicative-form DNA and RNA) were found in the mesenteric lymph nodes and spleens at 10 days after infection. The localization of positive cells in the middle of germinal centers suggested that they were B lymphoblasts. Circulating leukocytes and bone marrow cells also contained viral RNA, but the levels of replicative-form DNA were below detectability. The levels of viral DNA and RNA in adult mink cells replicating ADV were decreased compared with those in permissively infected cell cultures or neonatal mink, suggesting that the replication of ADV in adult mink might be semipermissive or restricted at some early stage of viral gene expression. The low level of viral replication and transcription in lymphoid cells might provide a mechanism for the development of immune disorders and for the maintenance of persistent infection. Single-stranded virion DNA was found in other organs, but the strand-specific probes made it possible to show that this DNA represented virus sequestration. In addition, glomerular immune complexes containing virion DNA were detected, suggesting that ADV virions, or perhaps free DNA, may have a role in the development of ADV-induced glomerulonephritis.

Agarose gel electrophoresis of bacteriophages and related particles

Viruses and related particles have been fractionated by electrophoresis through gels. For agarose gels, the radius at the exclusion limit for spheres varies from 1500 nm in a 0.04% gel to 3.6 nm in a 4.0% gel. Thus, the size of the gel's pores can be adjusted to sieve all known viruses. By measurement of electrophoretic mobility (mu) as a function of agarose concentration, the mu in the absence of a solid support (mu 0) can be determined for any particle. From the shape of a semilogarithmic plot of mu as a function of agarose percentage, a rod-shaped particle can be discriminated from a spherical particle. The sphere's radius can be determined from this plot with an accuracy of +/- 8%. Accuracy of +/- 1% has been more recently achieved using two-dimensional agarose gel electrophoresis. Though bacteriophages have been the primary object of study, the above techniques of agarose gel electrophoresis have also been applied to plant viruses and should be applicable to animal viruses. The mu 0 values measured for bacteriophages with and without their tail fibers suggest a mechanism of controlling attachment to a host. A related mechanism is proposed for the control of the virulence of animal viruses. Measurement of outer radius for different forms of the capsid of bacteriophage P22 reveals variability in outer radius too small to be detected by electron microscopy.

Restricted viral antibody specificity in many ferrets infected with the ferret Aleutian disease parvovirus. Brief report

The majority of ferrets infected with a ferret strain of Aleutian disease virus (ADV) produce antibody only to a detergent-sensitive common determinant on the two closely related virion proteins. Ferrets with high antibody titers and mink infected with this virus also produce antibody to one or more virion immunogenic determinants unaffected by detergent.

Restricted heterogeneity of the early antibody response to Aleutian disease virus in mink kits

Mink kits born of Aleutian disease (AD) negative dams were infected neonatally with different isolates of Aleutian disease virus (ADV). They were then sacrificed at different days after infection (10-45 days) and their sera were analysed by different techniques for concentrations of immunoglobulins and quality of the produced antibodies to ADV. The infected mink kits produced significantly higher concentrations of IgM and IgG immunoglobulins than non-infected-age matched control mink (p less than 0.001). Eight percent of the sera from the infected mink kits exhibited a restricted heterogeneous gammaglobulin profile as shown by serum electrophoresis. These findings were further investigated by other techniques such as SDS-PAGE and crossed serum line immunoelectrophoresis. It is concluded that mink kits when infected neonatally with ADV start to develop hypergammaglobulinemia soon after infection, and that a small percentage of the mink react with a gammaglobulin response of restricted heterogeneity.

Demonstration of non-degraded Aleutian disease virus (ADV) proteins in lung tissue from experimentally infected mink kits. Brief report

Isolates of ADV replicate to rather high quantities in lungs from neonatally infected mink kits. The virus was analysed for polypeptide composition, and for the first time high molecular weight polypeptides have been observed in in vivo produced ADVs. These polypeptides are analogous to those of in vitro produced ADVs. The molecular weights of the structural polypeptides of the low virulence Pullman ADV and the highly virulent DK and Utah I isolates of ADV were found to be 88kD and 78kD and in vivo produced ADV-G polypeptides were found to be 85kD and 75kD, the same molecular weights as those described for in vitro produced ADV-G. Presence of the ADV coded, non-structural polypeptide with the molecular weight of 71kD (p71) was also demonstrated in the lung tissue from mink kits.

Monoclonal antibodies against Aleutian disease virus distinguish virus strains and differentiate sites of virus replication from sites of viral antigen sequestration

Monoclonal antibodies (mAbs) were used to study antigenic differences among strains of Aleutian disease virus (ADV) and to characterize viral proteins in vitro and in vivo. A number of ADV field strains could be discriminated, and highly virulent Utah I ADV was clearly delineated from the tissue culture-adapted avirulent ADV-G strain. This specificity could be demonstrated by indirect immunofluorescence against infected cultures of Crandell feline kidney cells or against tissues of Utah I ADV-infected mink. Viral antigens were demonstrated in both the nuclei and the cytoplasm of infected tissue culture cells. However, in mink mesenteric lymph node, spleen, and liver, viral antigen was observed only in the cytoplasm. Absence of nuclear fluorescence suggested that the detected antigen represented phagocytized viral antigens rather than replicating virus. This conclusion was supported by the finding that mAbs reactive only against low-molecular-weight polypeptides derived from intact viral proteins gave the same pattern of in vivo fluorescence as mAbs with broad reactivity for large or small (or both) viral polypeptides. The distribution of infected cells was the same as that described for macrophages in these tissues and suggested that cells of the reticuloendothelial system had sequestered viral antigens.

Examination of Aleutian disease virus in charge-shift crossed immunoelectrophoresis

The surface properties of Aleutian disease virus were studied by charge-shift crossed immunoelectrophoresis. When different strains of Aleutian disease virus were treated with non-charged detergent followed by charged detergents, they showed bi-directional migration velocity shifts in electrophoresis, indicating amphiphilic surface properties of the virus.