Sabin attenuated LSc/2ab strain of poliovirus spreads to the spinal cord from a peripheral nerve in bonnet monkeys (Macaca radiata)

Vaccine-associated paralytic poliomyelitis is a serious concern while using the live attenuated oral polio vaccine for the eradication of poliomyeliti s. The bonnet monkey model of poliovirus central nervous system (CNS) infec tion following experimental inoculation into the ulnar nerve allows the com parative study of wild-type and attenuated poliovirus invasiveness. Dosages greater than or equal to 10(4) TCID50 of Mahoney strain of poliovirus type 1 [PV1(M)] result in paralysis. In contrast, even with 10(7) TCID50 of Sab in attenuated strain of poliovirus type 1 (LSc/2ab), no paralysis occurs, b ut virus spreads into the CNS where viral RNA is found in spinal cord neuro ns. While wild-type PV1(M) viral RNA replicates in neurons land possibly in glial cells) and in cells around vessel walls, which may be mononuclear or endothelial cells, attenuated Viral RNA is detected only in neurons. Syste mic viraemia and gastrointestinal virus shedding occurs only in PV1(M)-infe cted animals. While a systemic serologic response is detected in both group s of animals, cerebrospinal fluid antibodies are detected only in animals i nfected with PV1(M), Both the PV1(M) and LSc/2ab strains spread to the cerv ical spinal cord and then to the lumbar spinal cord following ulnar nerve i noculation. Neuronophagia acid neuronal loss are only seen in PV1(M)-infect ed monkeys in whom clinical paralysis is observed. Infection with LSc/2ab d oes not result in neuronophagia, neuronal loss or clinical paralysis. Sprea d of attenuated poliovirus in spinal cord neurons without causing paralysis following inoculation into the ulnar nerve is an important finding.