Abstract
Poliovirus vaccine coverage in Israel is over 90%. The last nine birth cohorts have been vaccinated exclusively with inactivated polio vaccine (IPV). However, between February and July 2013 type 1 wild poliovirus (WPV1) was detected persistently in 10 and intermittently in 8 of 47 environmental surveillance sites in southern and central Israel and in 30 stool samples collected during July from healthy individuals in southern Israel. We report results of sequence and phylogenetic analyses of genes encoding capsid proteins to determine the source and transmission mode of the virus. WPV1 capsid protein 1 nucleotide sequences were most closely related to South Asia (SOAS) cluster R3A polioviruses circulating in Pakistan in 2012 and isolated from Egyptian sewage in December 2012. There was no noticeable geographical clustering within WPV1-positive sites. Uniform codon usage among isolates from Pakistan, Egypt and Israel showed no signs of optimisation or deoptimisation. Bayesian phylogenetic time clock analysis of the entire capsid coding region (2,643 nt) with a 1.1% evolutionary rate indicated that Israeli and Egyptian WPV1-SOAS lineages diverged in September 2012, while Israeli isolates split into two sub-branches after January 2013. This suggests one or more introduction events into Israel with subsequent silent circulation despite high population immunity.
Highlights
Two major lineages of type 1 wild poliovirus (WPV1) are currently circulating in endemic countries: the South Asia (SOAS) lineage in Pakistan and Afghanistan, and a West African lineage (WEAFB1 and WEAFB2) in Nigeria [1]
The complete VP1 sequence of isolate 8099-PL9, sent to World Health Organization (WHO) and Centers for Disease Control and Prevention (CDC) for comparison with more contemporary wild poliovirus isolates, was most closely related to WPV1-SOAS cluster R3A isolated from environmental samples collected in Pakistan in 2012 and from sewage in Egypt in December 2012
This report describes the sequence analysis of progeny of a WPV1 that was introduced into Israel and established a sustained silent spread within a population that started with an average vaccine coverage of more than 95% and where the last nine birth cohorts were vaccinated exclusively with inactivated polio vaccine (IPV)
Summary
Two major lineages of type 1 wild poliovirus (WPV1) are currently circulating in endemic countries: the South Asia (SOAS) lineage in Pakistan and Afghanistan, and a West African lineage (WEAFB1 and WEAFB2) in Nigeria [1]. Both of these lineages occasionally spread to other countries with a high percentage of non-immunised children and have caused cases of acute flaccid paralysis (AFP) [2]. This introduction resulted in a local outbreak of poliomyelitis that subsequently spread to central Asia and Russia [7]
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