EVOLUTION OF MOUSE HEPATITIS-VIRUS (MHV) DURING CHRONIC INFECTION - QUASI-SPECIES NATURE OF THE PERSISTING MHV RNA

Coronavirus infection of mice has been used extensively as a model for the study of acute encephalitis and chronic demyelination. To examine the evolution of coronavirus RNA during chronic demyelinating infecti on, we isolated RNA from intracerebrally inoculated mice at 4, 6, 8, 1 3, 20, and 42 days postinfection and used reverse transcription-polyme rase chain reaction amplification methods (RT-PCR) to detect viral seq uences. RNA sequences from two viral structural genes, the spike gene and the nucleocapsid gene, were detected throughout the chronic infect ion. In contrast, infectious virus was not detectable from brain homon genates beyond 13 days postinfection. These results indicate that coro navirus RNA persists in the brain at times when infectious virus is no t detected. To determine if genetic changes were occurring during vira l replication in the host, we cloned and sequenced the RT-PCR products from the spike and nucleocapsid regions and analyzed the sequences fo r mutation's. Sequencing of the cloned products revealed that a variet y of mutant forms of viral RNA persisted in the CNS, including point m utants, deletion mutants, and termination mutants. The mutations accum ulated during persistent infection in both the spike and the nucleocap sid sequences, with greater than 65% of the mutations encoding amino a cid changes. These results show that a diverse population or quasispec ies consisting of mutant and deletion variant Viral RNAs (which may no t be capable of producing infectious virus particles) persists in the central nervous system of mice during chronic demyelinating infection. The implications of these results for the role of persistent viral ge netic information in the pathogenesis of chronic demyelination are dis cussed. (C) 1995 Academic Press, Inc.