Environmental surveillance of poliovirus in sewage water around the introduction period for inactivated polio vaccine in Japan

Abstract

Environmental virus surveillance was conducted at two independent sewage plants from urban and rural areas in the northern prefecture of the Kyushu district, Japan, to trace polioviruses (PVs) within communities. Consequently, 83 PVs were isolated over a 34-month period from April 2010 to January 2013. The frequency of PV isolation at the urban plant was 1.5 times higher than that at the rural plant. Molecular sequence analysis of the viral VP1 gene identified all three serotypes among the PV isolates, with the most prevalent serotype being type 2 (46%). Nearly all poliovirus isolates exhibited more than one nucleotide mutation from the Sabin vaccine strains. During this study, inactivated poliovirus vaccine (IPV) was introduced for routine immunization on 1 September 2012, replacing the live oral poliovirus vaccine (OPV). Interestingly, the frequency of PV isolation from sewage waters declined before OPV cessation at both sites. Our study highlights the importance of environmental surveillance for the detection of the excretion of PVs from an OPV-immunized population in a highly sensitive manner, during the OPV-to-IPV transition period.

FIG 1

Frequency of poliovirus (PV) and non-polio enterovirus (NPEV) isolation at two independent sewage plants. The frequencies and distributions of NPEV and poliovirus type 1, type 2, and type 3 isolated from plants T and Y over the 34-month collection period were compared. The double-headed arrows above each graph indicate scheduled vaccination periods in each area. The dotted vertical lines indicate the month and year when IPV was introduced in Japan. The first y axis (left) indicates the frequency of PV isolation for each month, and the second y axis (right) indicates the frequency of NPEV isolation for each month. Sample collection was conducted from April 2010 to January 2013 (x axis).

FIG 2

Distribution of nucleotide substitutions in the VP1 regions of the isolated strains of poliovirus (PV). The nucleotide divergence of VP1 between isolates and reference vaccine strains (Sabin 1 [GenBank accession number AY082688], Sabin 2 [accession number AY082679], and Sabin 3 [accession number AY082683]) is shown on the x axis. The number of isolates with each mutation is shown on the y axis.

FIG 3

Nucleotide substitutions in the VP1 region. The column above each nucleotide indicates the percentage of all PVs of an isolated serotype during the collection period that featured a mutation at this position. The circle below each codon shows the amino acid substitution resulting from the mutation. Capital letters below the nucleotides and in the circles represent conventional abbreviations for amino acids. The asterisk indicates that the OPV Sabin 3 strain originally contained a mutation at the second codon of the sixth amino acid of VP1, known as the “mixed-base position.”