How do ferrets get Aleutian disease virus?

Aleutian Disease (also ADV, for Aleutian Disease Virus) is a highly contagious parvovirus affecting mustelids, causing spontaneous abortion and death in minks and ferrets.

Aleutian disease virus is highly contagious. It is transferred through a ferret's bodily fluids, and it can be lie dormant in dried urine or on an owner's clothes and shoes for up to two years. Known cases of ADV positive ferrets should not be taken to places where they may come in contact with other ferrets. They also should not be allowed to run on floors or other areas where uninfected ferrets or their owners may come in contact with residual traces of the virus from the infected animals.

The Aleutian disease virus lays dormant in ferrets until stress or injury allows it to surface. While the parvovirus itself causes little or no harm to the ferret host, the large number of antibodies produced in response to the presence of the virus results in a systemic vasculitis, resulting in eventual renal failure, bone marrow suppression and death. The symptoms are chronic, progressive weight loss, lethargy, hepatomegaly and/or enlarged spleen, anemia, rear leg weakness, seizures and black tarry stool. Once symptoms show themselves, the disease progresses rapidly, usually to death within a few months.

Source: Wikipedia.org/wiki/Aleutian_Disease