Oral poliovirus vaccine type 3 from a patient with transverse myelitis is neurovirulent in a transgenic mouse model

BackgroundIt is accepted that oral poliovirus vaccine (OPV) can cause vaccine-associated paralytic poliomyelitis (VAPP) and that wild poliovirus infection can rarely present as transverse myelitis. It is therefore possible that OPV could cause transverse myelitis. We previously reported a case of transverse myelitis that developed in a 6-month-old boy, 7 days after receiving his second dose of OPV.ObjectivesOur aim was to test the virus from this patient with transverse myelitis for neurovirulence in a mouse model.Study designThe TgPVR21 transgenic mouse line, which expresses the human poliovirus receptor CD155, was used to assess neurovirulence of the viruses tested. Neurovirulence was expressed as the PD50, the dose of virus causing paralysis in 50% of the mice. Four type 3 polioviruses were tested: a prototype wild strain, a fully attenuated polio vaccine virus, a virus from a patient with VAPP and the virus from the patient with transverse myelitis.ResultsThe PD50 for the wild poliovirus strain was 3.83 and for the fully attenuated vaccine strain, 7.63. The PD50 for the two clinical isolates were between these values, ≧4.96 for the poliovirus known to have caused VAPP and ≧4.81 for the virus from the patient with transverse myelitis.ConclusionsThe report of an OPV strain from a transverse myelitis case being neurovirulent in an in vivo mouse model provides further evidence for a causal association between OPV and transverse myelitis.