Prevalence of vaccine-derived polioviruses in sewage and river water in South Africa

Abstract

Polioviruses (PVs) are not associated with waterborne transmission to the same extent as many other enteric viruses. However, they are typically transmitted by the faecal-oral route, which implies that the risk of infection by exposure to the viruses in water cannot be underestimated. The risk appears particularly high for rural communities, which use sewage-polluted river water for domestic purposes. Thus, the presence in the environment of highly evolved, neurovirulent vaccine-derived poliovirus (VDPV) strains in the absence of polio cases would have important implications for strategies to terminate immunisation with oral poliovirus vaccine (OPV) following global polio eradication. The aim of the current study was to determine the prevalence of VDPVs in selected sewage and river water samples collected from 2001 to 2003, and to construct phylogenetic trees of the partially sequenced 5′untranslated region (5′UTR) and the VP1 region of the genomes to deduce the genetic relatedness between the PV strains. Using the monolayer plaque assay, 703 plaques from sewage and 157 plaques from river water samples were analysed. Application of a RT-multiplex PCR revealed that 176 of these plaques were non-polio enteroviruses, and 49 were PV isolates. The Sabin-specific RTtriplex PCR revealed the presence of 29 Sabin PV type 1, 8 Sabin PV type 2 and 12 Sabin PV type 3 isolates. The 5′UTR and the VP1 region of 13 PV type 1, 7 PV type 3 and 6 PV type 2 isolates were partially sequenced. The majority of the OPV isolates (24 out of 26) displayed close sequence relationships (>99% VP1 sequence identity) to the parental Sabin PV vaccine strains and were classified as "OPV-like viruses". Two isolates (D1 08/28 and OF1 05/21) were found to be highly divergent and were classified as "suspected" VDPVs. Isolate OF1 05/21 (a "suspected" VDPV type 1) showed more than 0.9% divergence in VP1, whereas isolate D1 08/28 (a "suspected" VDPV type 2) showed 1.4% divergence in VP1 from the parental Sabin PV vaccine strains. As with most of the other OPV-like isolates, these "suspected" VDPVs were carrying mutations, which have previously been associated with reversion of the attenuated Sabin PV strains to increased neurovirulence. It was estimated that the total period of replication for the two "suspected" VDPVs was between 12 and 16 months. In conclusion, this study provided new and relevant information on the prevalence of "suspected" VDPVs in sewage and openUP river water, and opened the way to assess the possible broader significance of the findings reported here.

Comparative study of enteric viruses, coliphages and indicator bacteria for evaluating water quality in a tropical high-altitude system

“…The higher frequency of EV could be related to the massive polio vaccination campaigns that are carried out in Mexico three times a year for children of less than five years old. In previous studies, polio vaccine was isolated from both wastewater and river water two or three following the vaccination campaign [36-38]. Other studies are needed to ensure that the EV detected in the water samples used for irrigation corresponds to the vaccine type.…”

Neurovirulent Vaccine-Derived Polioviruses in Sewage from Highly Immune Populations

“…Recently introduced environmental surveillance programs in South Africa [34] Estonia[35], Slovakia [36], Japan [31] and Russia [37] also yielded aVDPVs. Thus we propose that similar long-term studies should be undertaken worldwide to assess how frequently VDPVs are present in the environment and the potential global risks posed by aVDPVs and iVDPVs.…”

Role of environmental poliovirus surveillance in global polio eradication and beyond

“…Highly diverged neurovirulent VDPVs have been isolated by ENV from many geographical locations such as Egypt, Greece, Haiti, India, South Africa and Switzerland [33,[42][43][44][45][46]. Two independent epidemiological sources of type 2 VDPV have been identified in central Israel.…”