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The ability of an avian retrovirus to cause central nervous system (CNS) disease was investigated in chickens infected in ovo with Rous associated virus-1. Viral envelope and core proteins and mature virions were found throughout CNS parenchyma, with the highest amounts localized in the granular layer of the cerebellum, in blood vessel endothelium, and the choroid plexus. This distribution was established by the time of hatching and persisted throughout the 14 weeks of observation. The highest levels of integrated proviral DNA and viral mRNA, were present in the cerebellum, consistent with the distribution of viral antigens. Mononuclear cell infiltrates were evident throughout the CNS, consistent with an inflammatory process. However, demyelination or vacuolar changes, as observed in other retroviral-induced CNS diseases, were not detected. Clinical symptoms of progressive neurologic dysfunction, i.e., weakness or paralysis of the hindlimbs, imbalance, and ataxia, were present in 7 of 38 infected chickens before termination of the experiment at 14 weeks posthatch. Viral antigens or lymphocyte infiltration were not detected in peripheral nerves. These findings suggest that the avian system may provide a valuable model to analyze the mechanisms governing retroviral induced CNS disease.

Widespread ultrastructural alterations in the vascular basal lamina were found in the central nervous system of symptomatic mice infected with three different neuropathogenic murine leukemia viruses. These changes appeared to progress in frequency and severity in parallel with the progression of spongiform lesions and clinical symptoms. Accumulations of pleomorphic, apparently degenerating, virions were frequently seen within areas that showed marked aberrations from the normal basal lamina ultrastructure. We suggest that the observed retrovirus-associated ultrastructural changes in the endothelial basal lamina may alter normal physiologic functions and thus play a primary role in the pathogenesis of retrovirus-induced spongiform disease.