Environmental surveillance detects poliovirus type 2 outbreaks in Israel

The wastewater environmental surveillance conducted in Jerusalem, Israel, has detected an increasing population of poliovirus type 2. Furthermore, these viral isolates are associated with vaccine-derived viral strains. A detailed report has recently been published in Eurosurveillance, Europe’s journal on infectious disease surveillance, epidemiology, prevention, and control.

Rapid communication: Emergence of genetically linked vaccine-originated poliovirus type 2 in the absence of oral polio vaccine, Jerusalem, April to July 2022. Image Credit: Kateryna Kon / Shutterstock

Background

Environmental surveillance programs aim to detect circulating pathogens in different sources involved in pathogen transmission. The most commonly used sources are wastewater, sewage, drinking water, air, and fomites. These programs are particularly needed to monitor the abundance of clinically undetected pathogens and their potency to cause public health hazards.

Israel’s environmental surveillance program covers 15 regions throughout the country, including 50% of the general population. In addition, Jerusalem has four non-overlapping surveillance regions.

Detection and genomic analysis of poliovirus type 2

Supplementary wastewater surveillance programs have increased the monitoring of poliovirus-related acute flaccid paralysis in Israel since 1989. The presence of poliovirus type 2 has been detected in two Jerusalem regions and one Central Israel region in April 2022.

By July 2022, the number of poliovirus type 2 detection in wastewater has been found to increase significantly in Jerusalem regions. In addition, the genomic sequencing of viral isolates has shown the accumulation of mutations over time.

In three different Jerusalem regions, two poliovirus type 2 isolates have been detected over a period of 100 days. The sequencing analysis has revealed that these isolates are associated with vaccine-derived poliovirus.

Five additional poliovirus type 2 isolates have been detected during the same period; however, these isolates are not linked to the vaccine-derived viral strain. The poliovirus type 2 sequences isolated in 2022 have been found to share a 2-nucleotide signature in the VP1 gene. This gene encodes the main viral capsid protein VP1.

To further identify the genetic linkage between isolates, whole genome sequencing has been conducted for the isolates collected between 2020 and 2022. The findings have shown the presence of additional mutations in the P1 genomic region across all sequences isolated in 2022. The P1 region includes VP1, VP2, VP3, and VP4 genes. However, these shared mutations were not present in the sequences isolated in 2020 and 2021.

Considering the P2/3 genomic region, recombination with a non-poliovirus enterovirus has been detected in the 3A gene. However, this recombination was absent in all poliovirus sequences isolated in 2020 and 2021.

Overall, these observations strongly identify genetic linkage across all poliovirus type 2 sequences isolated in 2022.

Study significance

Environmental surveillance in Israel has detected an increasing frequency of poliovirus type 2 isolates in different regions of Jerusalem. These isolates are genetically associated with the vaccine-derived poliovirus type 2 strain.

Vaccine-derived polioviruses primarily originate from genetically mutated oral poliovirus vaccine strains that accumulate mutations over time. A high rate of viral transmission in populations with low immunity, or a high rate of viral replication in immunocompromised patients, is responsible for the origination of vaccine-derived polioviruses.

Oral vaccination against poliovirus type 2 was terminated globally in April 2016 because of the emergence of vaccine-derived type 2 poliovirus-induced outbreaks. Therefore, monovalent oral poliovirus type 2 vaccination has been introduced as a preventive measure to control these outbreaks.

As of July 2022. Only localized transmission of poliovirus type 2 has been detected in Jerusalem. No incidence of virus-induced acute flaccid paralysis has been seen so far. To control these outbreaks, the Israel Ministry of Health has decided to immunize children with inactivated poliovirus vaccines.

Overall, the study highlights the significance of routine environmental surveillance in rapidly identifying outbreaks caused by vaccine-derived polioviruses and controlling outbreaks through rapid vaccination campaigns.