Provided are non-human animal model systems for viral pathogenesis of neurodegeneration, autoimmune demyelination, and autoimmune diseases such as diseases of the central nervous system, including multiple sclerosis (MS), and diabetes. Such non-human animal model systems may be suitably employed for the study of diseases such as MS and diabetes and for the identification and characterization of candidate therapeutic compounds and compositions for the treatment of such diseases. Also provided herein are markers and methods for the detection, in patients susceptible to autoimmune disease, of autoimmune diseases of the central nervous system such as progressive multifocal leukoencephalopathy (PML) following treatment with one or more therapeutic agent as exemplified herein by the therapeutic agent natalizumab. Exemplary animal model systems comprise marmosets infected with a herpesvirus such as HHV6-A and HHV6-B, transgenic mouse and zebrafish animal model systems wherein the transgene encodes CD46, and methods for monitoring the risks of patients having MS, diabetes and other auto-immune disorders treated with anti-adhesion molecules such as natalizumab.