When mink kits were infected neonatally with a highly virulent strain of Aleutian disease virus (ADV), 100% of both Aleutian and non-Aleutian genotype mink died of interstitial pneumonia characterized by permissive ADV infection of alveolar type H cells. Treatment of infected kits with either mink anti-ADV gamma globulin or mouse monoclonal antibodies against ADV structural proteins reduced mortality by 50 to 75% and * Corresponding author. sen, unpublished results), the accumulated information suggested that perhaps maternally transferred antibodies masked the development of pneumonia. By using immunofluorescence, Southern blot analysis, and strand-specific in situ hybridization, we previously showed that the acute pneumonia is caused by cytopathic replication of ADV in lung alveolar type II cells of newborn ADV antibody-negative mink kits. This infection is associated with high levels of viral antigen, viral DNA, the viral replicative forms (RFs) of DNA, and viral mRNA in each infected cell (7). In contrast, in mink infected as adults, viral replication and transcription are dramatically altered. The target cells lie within lymphoid organs (probably lymphocytes), and ADV expression is markedly restricted at the cellular level. That is to say, the level of viral RF DNA and mRNA is decreased by a factor of 10 to 100 and intranuclear viral protein, which is easily detected in infected mink kits, cannot be detected (6). One difference between adult and newborn mink is the rapid development of anti-ADV antibodies in adults, and we previously speculated that the restricted pattern seen in adults might be a result of the anti-ADV antibody responise (6). Similarly, we wondered whether the failure to observe pneumonia in ADV antibody-positive kits was due to some effect of maternally transferred antibodies. In the present study, we directly examnined the effect of passive anti-ADV antibodies on the replication of ADV and development of disease in neonatally infected mink kits. Our results showed that antibodies restrict viral replication at the cellular level, preventing the acute but not the chronic disease caused by ADV.

Different isolates of Aleutian mink disease parvovirus (ADV) were cloned and nucleotide sequenced. Analysis of individual clones from two in vivo-derived isolates of high virulence indicated that more than one type of ADV DNA were present in each of these isolates. Analysis of several clones from two preparations of a cell culture-adapted isolate of low virulence showed the presence of only one type of ADV DNA. We also describe the nucleotide sequence from map units 44 to 88 of a new type of ADV DNA. The new type of ADV DNA is compared with the previously published ADV sequences, to which it shows 95% homology. These findings indicate that ADV, a single-stranded DNA virus, has a considerable degree of variability and that several virus types can be present simultaneously in an infected animal.

DNA from one cell culture-adapted and two pathogenic strains of Aleutian disease of mink parvovirus (ADV) was molecularly cloned into the vectors pUC18 and pUC19. The DNA from the two pathogenic strains (ADV-Utah I and ADV-Pullman) was obtained from virus purified directly from the organs of infected mink, whereas the DNA from the nonpathogenic ADV-G was derived from cell culture material. The cloned segment from all three viruses represented a 3.55-kilobase-pair BamHI (15 map units) to Hindlll (88 map units) fragment. Detailed physical mapping studies indicated that all three viruses shared 29 of 46 restriction endonuclease recognition sites but that 6 sites unique to the pathogenic strains and 5 sites unique to ADV-G were clustered in the portion of the genome expected to code for structural proteins. Clones from all three viruses directed the synthesis of two ADV-specific polypeptides with molecular weights of approximately 57 and 34 kilodaltons. Both species reacted with sera from infected mink as well as with a monoclonal antibody specific for ADV structural proteins. Because production of these ADV antigens was detected in both pUC18 and pUC19 and was not influenced by isopropyl-lo-D-thiogalactopyranoside (IPTG) induction, their expression was not regulated by the lac promoter of the pUC vector, but presumably by promoterlike sequences found within the ADV DNA. The proteins specified by the clones of ADV-G were 2 to 3 kilodaltons smaller than those of the two pathogenic strains, although the DNA segments were identical in size. This difference in protein molecular weights may correlate with pathogenicity, because capsid proteins of pathogenic and nonpathogenic strains of ADV exhibit a similar difference.

Inhibition of precipitation in counter current electrophoresis was at least 32 times more sensitive when compared to the normal counter current electrophoresis for the demonstration of mink antibodies against Aleutian disease virus (ADV). ADV antigen can be produced from mink organs or in cell culture. The reactivity of the two types of antigen in the two kinds of counter current electrophoresis methods is described in this report. When 22 mink sera were titrated in normal counter current electrophoresis against cell culture produced antigen and organ produced antigen, significantly lower antibody titres were found with cell culture produced antigen. This difference was not found when inhibition of precipitation of counter current electrophoresis was used.

Four different isolates of Aleutian disease virus have been compared electrophoretically and serologically. These were the DK and Utah 1 isolates, known as highly virulent strains, the Pullman isolate, known as a low virulent strain and the avirulent ADV-G isolate, which is the only strain grown in cell culture. ADV-G was shown to migrate in agarose electrophoresis 22 per cent slower than the other strains. Several murine monoclonal antibodies were prepared against each of the isolates. Each one reacted with all 4 of the isolates, but a few showed higher affinity for some of the isolates. Competitive RIA analyses were also performed, and these studies indicated some serological differences between the 4 strains. It is concluded that ADV-G polypeptides are chemically different but immunologically cross-reacting with the polypeptides present on the field ADV strains. It is suggested that the small serological differences seen between the field strains might be caused by slightly different in vivo proteolytic degradation of the viral capsid proteins and thus might not be taken as an indication of strain variation.