Molecular epidemiology of silent introduction and sustained transmission of wild poliovirus type 1, Israel, 2013

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 WPV1positive 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.

Intensified environmental surveillance supporting the response to wild poliovirus type 1 silent circulation in Israel, 2013

“…Sequence analysis identified the virus isolates as WPV1 belonging to the SOAS lineage, with closest match to the virus isolated from sewage in Egypt in December 2012 [18]. The viral load in the sewage sample was calculated from the number of plaques isolated: by taking into consideration of the size of the sampled population, the number of faecal excretors of the virus could be roughly estimated to be tens or even hundreds of excretors, indicating ongoing indigenous circulation.…”

Lessons from a Public Health Emergency — Importation of Wild Poliovirus to Israel

“…1 The editorial was responding to California's firstin-the-nation broad medical-marijuana law and DEA agents' subsequent threats to revoke the DEA registrations of California physicians who suggested that a patient might benefit from marijuana as permitted by the new law. 2 California has now been joined by more than 20 additional states in permitting patients to possess marijuana on the advice of their physician (see table). There has, however, been no change in federal law -which still prohibits possession and sale of marijuana -and little change in the DEA's tactics.…”

“…Since the last poliomyelitis outbreak in Israel in 1988, 1 the country has developed the capacity in our environmental laboratories to detect pathogens such as polioviruses in very low quantities within large volumes of sewage, and we have fully deployed this high-sensitivity detection on a national scale. This system routinely covered approximately 30 to 40% of the population in a representative fashion, 2 and it was substantially intensified beginning in June 2013, shortly after the detection of the wild poliovirus importation. The number of sewage sites being sampled increased from a range of 8 to 10 per month to 80 per month at the height of the effort, to keep up with poliovirus activity.…”

“…The virus found in these samples was closely related to polioviruses that have been circulating in polioendemic Pakistan since 2012 and to the poliovirus that had been isolated from sewage samples in neighboring Egypt in December 2012. 2 This public health emergency posed two major challenges for decision makers in Israel. The first one concerned the sustainability and interpretation of our supplementary environmental surveillance.…”

“…The number of sewage sites being sampled increased from a range of 8 to 10 per month to 80 per month at the height of the effort, to keep up with poliovirus activity. 2 The coverage of the sampling was thereby expanded to include as much as 80% of Israel's population, and the sampling frequency was increased from monthly to weekly.…”