Lentivirus Infections of Ungulates. Iii. Pathogenesis & Symptoms

The term “slow infection” was introduced for the first time by the Icelandic researcher B. Sigurdsson in 1954 (Sigurdsson, 1954). With this term, he designated the interaction of the virus with the host, characterized by a prolonged (many months and even years) incubation period, at what time several organs or systems become affected and thereafter, results in slow, but progressive development of symptoms of the disease and an inevitable death. Fifty years later, the agents of classical slow infections (the maedi-visna virus, the caprine arthritis-encephalitis virus, the feline, simian and human immunodeficiency viruses) were put together with other philogenetically related retroviruses (the equine infectious anaemia virus, the bovine immunodeficiency virus and the Jembrana disease virus) in the Lentivirinae family. Not all lentiviruses correspond to the criteria of Sigurdsson. The Jembrana disease for instance is characterized with acute course, the equine infectious anaemia (EIA) occurs both acutely and chronically, maedi-visna (MV) in sheep and caprine arthritis encephalitis (CAE) are classical slow infections and as to the persistent bovine immunodeficiency (BI) infections, by recently it is not known if it has a clinical stage. In the process of evolutionary divergence, lentiviruses (LV) have preserved some common traits and acquired new ones, conditioning clinicopathomorphological variations of their interaction with host’s organism.