The following is excerpted from the article here: http://www.ferret-universe.com/health/adv.html
“ADV is a highly contagious Parvovirus (composed mainly of protein DNA) with differing strains and strengths characterized by a persistent viral infection which causes a huge increase in antibodies found in the blood known as hypergammaglobulinemia, and has been around since the late 1960's. The antibodies combine with ADV and are deposited within tissues of multiple organs in the body causing inflammation. Unlike other viruses, the body is not able to initiate an effective immune response to fight the virus. The virus can very be spread through feces, urine, saliva and other body fluids as well as transmitted by human contact. Once clinical signs are present (renal failure, weight loss, splenomegaly, neurological symptoms like seizures and clotting abnormalities), disease will progress claiming the life of the ferret, usually within a few months.”
So far, this disease is incurable. Treatment consists of medicating/managing the symptoms.
There are many testing options available and your ferret vet should be more than happy to acquaint you with them. Each ferret in your home should be tested and then again at six months... this way a potential carrier shows up. Also, any ferret coming into your home should be tested as well to avoid potential infection.
As it can also be spread by human contact, if you must interact with a strange ferret, please take proper precautions before handling yours after. Proper hand sanitizing and clothing change is necessary.
ADV interferes with the immune system, so it might also leave your ferret at risk for other, serious diseases.