Measles virus encephalitis in ferrets as a model for subacute sclerosing panencephalitis

Young adult ferrets were used as experimental animals to study subacute sclerosing panencephalitis (SSPE). When cells infected with cell-associated measles virus strains isolated from SSPE patients were inoculated intracerebrally (i.c.) into ferrets, they developed an acute encephalitis and died within 1 to 3 weeks without detectable antibody formation. Immunization with live measles vaccine 5 weeks before i.c. inoculation changed the course of the infection in about 50% of the ferrets. These animals developed a subacute encephalitis within weeks or months after inoculation. Cell-associated measles virus was isolated from their brains and high measles antibody titers were found in their sera, comparable to those in sera of SSPE patients. Measles virus specific immunoglobulins (IgG) were present in their brains and determination of IgG/albumin ratios indicated that antibodies were synthesized in the brain in response to the persistent measles virus infection. Measles specific oligoclonal IgG bands were found in the sera and spinal fluids of these animals. Therefore, subacute ferret encephalitis has virological and immunological characteristics in common with SSPE, indicating that it may serve as a model for the human disease. Other animal models of SSPE are described briefly.