Characterization of genetic changes occurring in attenuated poliovirus 2 during persistent infection in mouse central nervous systems.

Genomic changes occurring in the attenuated W-2 strain of poliovirus 2 during persistent infection of the central nervous system of immunosuppressed mice were analyzed. The RNase T1 oligonucleotide fingerprints of 34 different viruses, isolated from the brains and spinal cords of paralyzed and nonparalyzed mice during a 105-day period, were used to quantitate and compare the mutations occurring in each isolate. Although mice were inoculated with plaque-purified virus, genetically distinct viruses were recovered from the central nervous system. The number of oligonucleotide changes occurring in isolates from paralyzed mice generally was greater than that observed in isolates from nonparalyzed mice. However, differences in the extent of mutation in isolates from the two groups of mice did not appear to be related to the level of virus replication. In paralyzed mice, the number of oligonucleotide changes on average was greater in viruses isolated during the first 60 days of the infection than in the last 45 days. The number of oligonucleotide changes was essentially constant throughout the infection, however, in viruses isolated from the brains of nonparalyzed mice. In addition, several specific oligonucleotide changes were found only in viruses isolated from paralyzed animals.