Subacute sclerosing panencephalitis in the hamster. Ultrastructure of the acute disease in newborns and weanlings.

Acute subacute sclerosing panencephalitis has been investigated in both newborn and weanling hamsters intracerebrally inoculated with a human subacute sclerosing panencephalitis isolate (HBS) adapted to grow in hamster central nervous system (CNS) tissue. Newborn animals developed a disease which was fatal in approximately 1 week whereas most weanlings showed signs of an acute disease after day 8, from which a significant number recovered. Ultrastructurally, the human subacute sclerosing panencephalitis isolate (HBS) replicated rapidly in the CNS of newborn hamsters in the absence of an immune response. Giant cells developed from neurons and some demyelination was evident, most probably due to oligodendrocytic damage. Virus replication involved the proliferation of both typical measles virions and morphologically defective particles. Intracytoplasmic viral nucleocapsids were seen, but none were found within nuclei during the acute disease in newborns. Weanling hamsters developed a demonstrable immune response approximately 6 days after inoculation. Virions were seen and the majority appeared morphologically defective, lacking the associated nucleocapsids beneath the viral envelope. Abundant intranuclear, as well as intracytoplasmic, viral inclusions were seen. The results are of significance in the examination of myxoviruses (a group frequently linked to a number of chronic diseases of the CNS), in terms of viral replication in the CNS, in the response of different CNS cell types to infection, and in the influence of age and immune status upon the course of CNS disease.