Advanced environmental surveillance and molecular analyses indicate separate importations rather than endemic circulation of wild type 1 poliovirus in Gaza district in 2002

Abstract

An improved sewage surveillance algorithm (sample acquisition, processing, and molecular analysis) for wild and vaccine-derived polioviruses was developed and validated. It was based on plaque isolation with sensitive and high-throughput methods. The molecular analysis included sequencing; a comparison of the type, rate, and distribution of nucleotide substitutions with a profile for outbreaks evolving from a single progenitor; and phylogenetic analysis for relative similarity. The analyses revealed that two environmental wild type 1 isolates from the Gaza district in 2002 were imported separately, most likely from Egyptian southern governorates, and were not linked by endemic circulation. These findings illustrate the continuous spreading potential of wild-type poliovirus and underscore the value of extensive environmental surveillance employing advanced molecular analysis to monitor wild poliovirus in poliomyelitis-free regions.

FIG. 1.

Phylogenetic relationship between wild poliovirus environmental isolates from Gaza and southern governates in Egypt. Consensus neighbor-joining phylogenetic trees were constructed by using the ClustalX program (22) with sequence data bootstrapped 1,000 times. Trees were visualized by using njplot (M. Gouy, Laboratoire de Biometrie et Biologie Evolutive, Université Lyon, CNRS, Lyon, France [http://pbil.univ-lyon1.fr/software/njplot.html]).