Comparison of simian immunodeficiency virus and human immunodeficiency virus encephalitides in the immature host.

The simian immunodeficiency virus (SIV) is closely related to the human immunodeficiency virus (HIV) in genomic organization and morphology. More important, SIV and HIV are both primate lentiviruses that cause transmissible immunodeficiency and encephalitis, with an apparently increased virulence in the immature host. The neuropathological features in common between SIV encephalitis in juvenile macaque monkeys and HIV encephalitis in children include the invasion of brain with virus-laden macrophages, the formation of multinucleated (syncytial) giant cells, and white matter lesions and subtle white matter astrocytosis. Important differences include giant cell leptomeningitis and evidence of necrosis and karyorrhexis in brain macrophage infiltrates in SIV-infected monkeys. These changes probably represent a more acute inflammatory process. The importance of future studies to define pathogenetic features of SIV encephalitis, using molecularly characterized isolates with varying neurovirulence and host range, are emphasized.