Strand-specific hybridization probes were utilized in in situ molecular hybridization specifically to localize replicative form DNA of Aleutian mink disease parvovirus (ADV). Throughout in vitro infection, duplex replicative form DNA of ADV was located in the cell nuclei. Single-stranded virion DNA and capsid proteins were present in the nuclei early in infection, but were later translocated to the cytoplasm. In neonatal mink, ADV causes acute interstitial pneumonia, and replicative forms of viral DNA were found predominantly in alveolar type II cells of the lung. Viral DNA was also found in other organs, but strand-specific probes made it possible to show that most of this DNA represented virus sequestration. In addition, glomerular immune complexes containing intact virions were detected, suggesting that ADV virions may have a role in the genesis of ADV-induced glomerulonephritis.

Information was sought on the comparative pathogenicity of four North American strains (isolates) of Aleutian disease virus for royal pastel (a non-Aleutian genotype) and sapphire (an Aleutian gejnotype) mink. The four strains (Utah-1, Ontario [Canada], Montana, and Pullman [Washington]), all of mink origin, were inoculated intraperitoneally and intranasally in serial 10-fold dilutions. As indicated by the appearance of specific antibody (counterimmunoelectrophoresis test), all strains readily infected both color phases of mink, and all strains were equally pathogenic for sapphire mink. Not all strains, however, regularly caused Aleutian disease in pastel mink. Infection of pastel mink with the Utah-1 strain invariably led to fatal disease. Infection with the Ontario strain caused fatal disease nearly as often. The Pullman strain, by contrast, almost never caused disease in infected pastel mink. The pathogenicity of the Montana strain for this color phase was between these extremes. These findings emphasize the need to distinguish between infection and disease when mink are exposed to Aleutian disease virus. The distinction has important implications for understanding the natural history of Aleutian disease virus infection in ranch mink.

Information was sought on the varied responses of royal pastel mink (a non-Aleutian genotype) to Aleutian disease virus of low virulence. Thus, of 20 yearling female pastel mink inoculated subcutaneously with a large amount of the Pullman strain of Aleutian disease virus, only 3 succumbed to the disease. Of the other 17 mink, 3 had neither viremia nor a rise in level of serum gamma globulin during the 24 weeks after inoculation. The other 14 mink were viremic for variable periods during the first 12 weeks. In only five mink was the viremia accompanied by elevated levels of serum gamma globulin, usually from week 8 on. Of the 16 subclinically infected mink that did not succumb to intercurrent disease and otherwise remained healthy, 9 were examined at 19 to 31 months for persisting virus. In only one mink, small amounts were detected in the mesenteric lymph node and spleen nearly 28 months after inoculation. The other seven mink that survived the infection were not protected when challenged 31 months later with a small amount of the highly virulent Utah-1 strain. Even though still poorly understood, these varied responses of the royal pastel mink to infection with Aleutian disease virus of low virulence have important pathogenetic and epidemiological implications.

Information was sought on the temporal replication of Aleutian disease virus in 27 royal pastel mink. Groups of three were examined 8 to 126 days after they were inoculated subcutaneously with 103 50% lethal doses of the Pullman strain. Much individual variation was noted in the onset of infection, occurrence of viremia, and extent of virus replication in the tissues. Thus, virus was detected in lymph nodes regional to the site of inoculation in only some mink during the first 14 days after inoculation. During this period, virus was often present as well in the mesenteric lymph node and spleen. First detected on day 10, viremia was present in all mink examined on day 28 but occurred irregularly thereafter, even when virus was widespread in the tissues. Except in five mink succumbing to the disease, the tissue distribution of virus after day 28 tended to be more limited, and the titers were generally lower than they had been earlier. Even though present in the lymph nodes and spleen, virus was often absent from the kidney, liver, and intestine after day 28. Specific antibody was detected on day 28 and was present in all mink thereafter, ostensibly without any adverse effect on virus replication. In most mink, the infection was considered subclinical, for it was usually not accompanied by a rise in serum gamma globulin or by morphologic evidence of the disease. The virologic findings in this study have a bearing on the relationship of subclinical infections to both horizontal and vertical transmission of the virus.