A retrospective cohort study estimating the individual Aleutian disease progress in female mink using a VP2 ELISA and its association to reproductive performance.

Aleutian Disease (AD) is an important disease in mink characterized by a persistent chronic infection typically causing a progressive disease with symptoms such as weight loss, polydipsia, polyuria, reduced reproductive performance and increased herd mortality. Due to lack of success in eradicating AD by stamping out, disease control programs based on estimating the disease progression have been implemented and used in the selection of future breeding animals. The aim of this project was to evaluate the association between the reproductive performance of female mink (expressed as being barren or not and litter size of non-barren females) and the individual AD status (defined as diseased or non-diseased based on the OD450 value in a dried blood spot samples (DBS) VP2 ELISA) while controlling for age and color type. The project included a pilot study with data on OD450 values and reproductive performance of 2067 female mink in one herd and a follow-up study with data from 10,368 primiparous female mink in four different herds. To investigate the association between the reproductive performance and the AD status, a multivariable zero-inflated Poisson regression model was used in the pilot study and an univariable mixed-effect logistic and Poisson regression model was used in the follow-up study. In the pilot study, being barren was significantly associated with age in an interaction with the AD status of the female mink with the highest risk among the primiparous diseased mink and lowest risk among older non-diseased mink (OR=5.8; p<0.001). In addition, color type was significantly associated with being barren. Age was also significantly associated with litter size, where older female mink gave birth to approximately 5% larger litters. However, no significant association was found between the litter size and the AD status of the female mink. In the follow-up study, both being barren as well as litter size were significantly associated with the AD status of the female mink (OR=1.6 (p<0.001) and IRR=-0.95 (p<0.001), respectively). Our results demonstrated an association between the reproductive performance of the female mink and the individual AD status. The effect of disease on litter size was minor compared to the effect on the barren percentage. Thus, assessment of the AD status with the DBS VP2 ELISA can be concluded to be a valuable tool for improving the reproductive performance of mink herds. Selection of primiparous female mink with low OD450 values for breeding will reduce the risk of having barren females.

Identification of aleutian mink disease parvovirus capsid sequences mediating antibody-dependent enhancement of infection, virus neutralization, and immune complex formation.

Aleutian mink disease parvovirus (ADV) causes a persistent infection associated with circulating immune complexes, immune complex disease, hypergammaglobulinemia, and high levels of antiviral antibody. Although antibody can neutralize ADV infectivity in Crandell feline kidney cells in vitro, virus is not cleared in vivo, and capsid-based vaccines have proven uniformly ineffective. Antiviral antibody also enables ADV to infect macrophages, the target cells for persistent infection, by Fc-receptor-mediated antibody-dependent enhancement (ADE). The antibodies involved in these unique aspects of ADV pathogenesis may have specific targets on the ADV capsid. Prominent differences exist between the structure of ADV and other, more-typical parvoviruses, which can be accounted for by short peptide sequences in the flexible loop regions of the capsid proteins. In order to determine whether these short sequences are targets for antibodies involved in ADV pathogenesis, we studied heterologous antibodies against several peptides present in the major capsid protein, VP2. Of these antibodies, a polyclonal rabbit antibody to peptide VP2:428-446 was the most interesting. The anti-VP2:428-446 antibody aggregated virus particles into immune complexes, mediated ADE, and neutralized virus infectivity in vitro. Thus, antibody against this short peptide can be implicated in key facets of ADV pathogenesis. Structural modeling suggested that surface-exposed residues of VP2:428-446 are readily accessible for antibody binding. The observation that antibodies against a single target peptide in the ADV capsid can mediate both neutralization and ADE may explain the failure of capsid-based vaccines.

Replication of Aleutian mink disease parvovirus in mink lymph node histocultures.

Aleutian mink disease parvovirus (ADV), causes an immune disorder with a persistent infection of lymphoid organs in adult mink. We studied replication of ADV in gel-supported histocultures prepared from adult mink mesenteric lymph node (MLN). Evidence of virus replication in the histocultures was first observed by indirect immunofluorescence 72 h after incubation with virus. Cells resembling lymphocytes and macrophages contained both ADV capsid (VP2) and nonstructural (NS1 and NS2) proteins, and were present in a distribution suggestive of infected cells within germinal centres. ADV replicative form and encapsidated virion DNA were also detected in infected histocultures at time-points after 72 h. In addition, we were able to passage ADV-Utah to a new round of histocultures. These results suggested that the infected cells were actual target cells for ADV replication and that productive ADV-Utah replication, complete with the generation of virus, was occurring in the histocultures. The mink MLN histocultures provide a system to study the replication and molecular pathogenesis of ADV in target tissues.

Role of alveolar type II cells and of surfactant-associated protein C mRNA levels in the pathogenesis of respiratory distress in mink kits infected with Aleutian mink disease parvovirus.

Neonatal mink kits infected with Aleutian mink disease parvovirus (ADV) develop an acute interstitial pneumonia with clinical symptoms and pathological lesions that resemble those seen in preterm human infants with respiratory distress syndrome and in human adults with adult respiratory distress syndrome. We have previously suggested that ADV replicates in the alveolar type II epithelial cells of the lung. By using double in situ hybridization, with the simultaneous use of a probe to detect ADV replication and a probe to demonstrate alveolar type II cells, we now confirm this hypothesis. Furthermore, Northern (RNA) blot hybridization showed that the infection caused a significant decrease of surfactant-associated protein C mRNA produced by the alveolar type II cells. We therefore suggest that the severe clinical symptoms and pathological changes characterized by hyaline membrane formation observed in ADV-infected mink kits are caused by a dysfunction of alveolar surfactant similar to that observed in respiratory distress syndrome in preterm infants. However, in the infected mink kits the dysfunction is due to the replication of ADV in the lungs, whereas the dysfunction of surfactant in preterm infants is due to lung immaturity.

Pathogenesis of Aleutian mink disease parvovirus infection: effects of suppression of antibody response on viral mRNA levels and on development of acute disease.

We suppressed the B-cell development and antibody response in mink by using treatment with polyclonal anti-immunoglobulin M (anti-IgM) to study the effects of antiviral antibodies on development of Aleutian mink disease parvovirus (ADV)-induced disease in more detail. Newborn mink kits were injected intraperitoneally with 1 mg of either anti-IgM or a control preparation three times a week for 30 to 34 days. At 21 days after birth, groups of mink kits were infected with the highly virulent United isolate of ADV. At selected time points, i.e., postinfection days 9, 13, 29, and 200, randomly chosen mink kits were sacrificed, and blood and tissues were collected for analyses. The efficacy of immunosuppressive treatment was monitored by electrophoretic techniques and flow cytometry. Effects of treatment on viral replication, on viral mRNA levels, and on development of acute or chronic disease were determined by histopathological, immunoelectrophoretic, and molecular hybridization techniques. Several interesting findings emerged from these studies. First, antiviral antibodies decreased ADV mRNA levels more than DNA replication. Second, suppression of B-cell development and antibody response in mink kits infected at 21 days of age resulted in production of viral inclusion bodies in alveolar type II cells. Some of these kits showed mild clinical signs of respiratory disease, and one kit died of respiratory distress; however, clinical signs were seen only after release of immunosuppression, suggesting that the production of antiviral antibodies, in combination with the massive amounts of free viral antigen present, somehow is involved in the induction of respiratory distress. It is suggested that the antiviral antibody response observed in mink older than approximately 14 days primarily, by a yet unknown mechanism, decreases ADV mRNA levels which, if severe enough, results in restricted levels of DNA replication and virion production. Furthermore, such a restricted ADV infection at low levels paves the way for a persistent infection leading to immunologically mediated disease. The potential mechanisms of antibody-mediated restriction of viral mRNA levels and mechanisms of disease induction are discussed.

Pathogenesis of disease caused by Aleutian mink disease parvovirus.

A review of the pathogenesis of Aleutian mink disease parvovirus (ADV) infection based on recent knowledge gained by the author and collaborators is given. The review focuses mainly on the following topics. 1) Development of an easy, sensitive and fast assay for detection of ADV antigens and antibodies directed against these antigens. A highly sensitive rocket line immunoelectrophoretic assay (RLIE) was developed. This assay turned out to be 32 times more sensitive than the counter current electrophoresis assay routinely used to detect anti-ADV antibodies in ADV eradication programs, and moreover, ADV associated antigens could simultaneously be quantitatively detected in the same electrophoretic run. Later, the assay was improved to make it more economical and easy to use and finally the assay, now termed the counter current line absorption immunoelectrophoresis (CCLAIE) assay, was slightly modified to adapt the test to screening programs. 2) Examination of surface properties of the virus and the antigens expressed during in vivo infection. In this chapter studies on the surface charge properties of ADV are described. Using charge-shift crossed immunoelectrophoresis the occurrence of amphiphilic proteins associated with ADV is shown and the significance of these findings in regard to biological properties are discussed. The first demonstration of intact ADV structural and nonstructural proteins in mink tissues is described and it is shown that the structural proteins of the cell culture adapted strain of ADV (ADV-G) also in vivo is 2-3000 dalton smaller than those of other ADVs, i.e. 75,000 and 85,000 dalton in ADV-G as opposed to 78,000 and 88,000 dalton in the other ADVs. 3) Studies on the pathogenesis of interstitial pneumonia caused by ADV in newborn mink kits. The features of ADV-induced interstitial pneumonia are described. Using Southern blot and in situ hybridization techniques it is shown that ADV replicates to high levels in alveolar type II cells and it is suggested that the permissive replication of the virus in these cells causes direct cytopathology, followed by decreased surfactant production and development of the characteristic clinical and pathological features of respiratory distress and hyaline membrane disease. 4) Comparison of the pathogenesis of acute versus chronic disease caused by ADV infection. The data obtained by in situ hybridization analysis of ADV infected adult mink, mink kits, and mink kits treated with anti-ADV antibodies are compared. The accumulated data suggested that the development of severe acute ADV-induced disease is linked to low or absent antibody titers paired with high levels of viral replication.(ABSTRACT TRUNCATED AT 400 WORDS)

Keratoconjunctivitis sicca.

KCS in man is often associated with a systemic disease whose pathogenesis is still obscure. A spontaneous animal model resembling Sjögren's syndrome has been developed in the NZB and NZB-NZW mouse. Other spontaneous animal models analagous to lupus erythematosis and polyarteritis have been found in dogs and Aleutian mink, respectively. Studies of the eyes and lacrimal glands in such animals, and in dogs with distemper, should be pursued. A viral etiology is implicated in each of the models. The roles of both the main and accessory lacrimal glands in normal and KCS eyes have been discussed, as well as drug-induced KCS and opportunities for its further investigation and treatment.

[Pathogenesis of aleutian mink disease. VII. Chronic hepatitis with bile duct proliferation]. / Die Pathogenese der Aluetenkrankheit der Nerze. VII. Chronische Hepatitis mit Gallengangproliferation

Aleutian disease is a chronic persistent viral infection of mink characterized by hypergammaglobulinema, generalized plasmacytosis, sclerosing glomerulonephritis, polyarteritis, and plasma cell hepatitis with bile duct proliferation. The development of hepatic lesions was studied both light- and electron-microscopically in mink experimentally infected with Aleutian disease virus. Fifteen normal and 99 mink experimentally infected with Aleutian disease virus were used. Experimental mink were killed in intervals from 3 weeks to 23 months after infection, and liver sections were processed for both light- and electron-microscopic studies. Experimentally infected mink developed portal and intralobular lymphocytic and plasmacytic infiltrates in the liver 3 weeks after infection. Four to five weeks after infection there was evidence of early bile duct proliferation that began as an outgrowth of the portal bile ducts. Three to five months after infection a marked bile duct proliferation was present in some of the portal triads and adjacent liver lobules; but there was no tendency of these lesions to progress into biliary cirrhosis. Ultrastructural characteristics of proliferating bile duct cells were marked deformation, formation of multiple cell layers, reduction in the number of microvilli and desmosomes, and infiltration of the epithelial cells by lymphoid cells and plasmacytes. The hepatic lesions either develop by direct virus stimulation or by the deposition of virus-antibody complexes.

Pathogenesis of aleutian disease of mink: identification of nonpersistent infections.

Aleutian disease virus usually produces a persistent infection and progressive immune comples disease in mink of the Aleutian genotype. Study of Aleutian disease virus infection in non-Aleutian mink showed that about one-quarter developed nonpersistent infections by the virus, and that the nonpersistence was not genetically determined by the host. The nonpersistently infected mink developed only a transient elevation of serum gamma globulin, and much lower specific Aleutian disease virus antibody titers than persistently infected mink. No lesions were found in the nonpersistently infected mink.

The pathogenesis of Aleutian disease of mink. 3. Immune complex arteritis.

Mink chronically infected with Aleutian disease virus develop a severe necrotizing arteritis affecting muscular arteries. Acute, subacute and healing lesions may be found. Extracellular deposits of host immunoglobulin and complement and, after acid elution, viral antigen can be shown by immunofluorescence technics in areas of fibrinoid necrosis and between proliferating endothelial cells. No intracellular viral antigen was found, indicating that the virus probably does not replicate in vascular structures. The arteritis of Aleutian disease appears to be the result of immune complex deposits in vessel walls.