Molecular and antigenic characterization of a highly evolved derivative ofthe type 2 oral poliovaccine strain isolated from sewage in Israel

An unusual, highly diverged derivative of the Sabin type 2 oral poliovaccin e (OPV) strain was recovered from environmental samples during routine scre ening for wild polioviruses. Virus was cultivated in L20B cells and then pa ssaged on BGM cells at 40 degrees C (RCT [reproductive capacity at supraopt imal temperature]-positive marker) to select against most OPV strains. All but 1 of 25 RCT-positive OPV-derived environmental isolates were antigenica lly and genetically (>99.5% VP1 sequence match) similar to the respective S abin strains. However, isolate PV2/4568-1/ISR98 (referred to below as 4568- 1) escaped neutralization with Sabin 2-specific monoclonal antibodies and c ross-adsorbed sera, and had multiple nucleotide substitutions (220 of 2,646 ; 8.3%) in the P1 capsid region. Fourteen of the 44 associated amino acid s ubstitutions in the capsid mapped to neutralizing antigenic sites. Neutrali zing titers in the sera of 50 Israeli children 15 years old were significan tly lower td 4568-1 (geometric mean titer [GMT], 47) than to Sabin 2 (GMT, 162) or to the prototype wild strain, PV2/MEF-1/EGY42 (GMT, 108). Two key a ttenuating sites had also reverted in 4568-1 (A(481) to G in the 5' untrans lated region and the VP1 amino acid I-143 to T), and the isolate was highly neurovirulent for transgenic mice expressing the poliovirus receptor (PVR- Tg21 mice). The extensive genetic divergence of 4568-1 from the parental Sa bin 2 strain suggested that the virus had replicated in one or more people for similar to 6 years. The presence in the environment of a highly evolved , neurovirulent OPV-derived poliovirus in the absence of polio cases has im portant implications for strategies for the cessation of immunization with OPV following global polio eradication.