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

Department of Microbiology and Virology, Christian Medical College Hospital, 632004, Vellore, India 1 Department of Pediatrics, Section of Infectious Diseases, University of Colorado Health Sciences Center, Box B140, 4200 East 9th Avenue, Denver, CO 80262, USA 2 Author for correspondence: Esther Ponnuraj (at University of Colorado Health Sciences Center). Fax +1 303 315 4892. e-mail esther.ponnuraj{at}uchsc.edu Vaccine-associated paralytic poliomyelitis is a serious concern while using the live attenuated oral polio vaccine for the eradication of poliomyelitis. The bonnet monkey model of poliovirus central nervous system (CNS) infection following experimental inoculation into the ulnar nerve allows the comparative study of wild-type and attenuated poliovirus invasiveness. Dosages 10 4 TCID 50 of Mahoney strain of poliovirus type 1 [PV1(M)] result in paralysis. In contrast, even with 10 7 TCID 50 of Sabin attenuated strain of poliovirus type 1 (LSc/2ab), no paralysis occurs, but virus spreads into the CNS where viral RNA is found in spinal cord neurons. While wild-type PV1(M) viral RNA replicates in neurons (and 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. Systemic viraemia and gastrointestinal virus shedding occurs only in PV1(M)-infected animals. While a systemic serologic response is detected in both groups of animals, cerebrospinal fluid antibodies are detected only in animals infected with PV1(M). Both the PV1(M) and LSc/2ab strains spread to the cervical spinal cord and then to the lumbar spinal cord following ulnar nerve inoculation. Neuronophagia and neuronal loss are only seen in PV1(M)-infected monkeys in whom clinical paralysis is observed. Infection with LSc/2ab does not result in neuronophagia, neuronal loss or clinical paralysis. Spread of attenuated poliovirus in spinal cord neurons without causing paralysis following inoculation into the ulnar nerve is an important finding.