Poliovirus infection of cyclophosphamide-treated mice results in persistence and late paralysis: II. Virologic studies.

An attenuated human poliovirus infection of cyclophosphamide (CY)-treated mice resulted in a persistent CNS infection. Persistence in asymptomatic animals occurred in 46% of CY-treated mice but in only 3% of untreated animals, and was confined primarily to the brain. Virus replication in the brain peaked by day 3 for all inoculum dilutions, but was lower with diluted virus. High virus titers in the spinal cord were found only in paralyzed animals and occurred late in the infection following inoculation of diluted virus. Thus, the level of virus replication in the brain was directly related to the amount of virus inoculated, and was correlated with the rapidity of virus transit to the spinal cord and the incubation time to paralysis.