Wastewater environmental surveillance conducted in Jerusalem, Israel has detected an increasing population of poliovirus type 2. In addition, these viral isolates are associated with vaccine-derived virus strains. A detailed report was recently published in euro surveillanceEurope’s Journal of Surveillance, Epidemiology, Prevention and Control of Infectious Diseases.
Rapid communication: emergence of genetically linked vaccine-derived poliovirus type 2 in the absence of oral polio vaccine, Jerusalem, April-July 2022. Credit: Kateryna Kon/Shutterstock
Environmental monitoring programs aim to detect circulating pathogens in various sources involved in pathogen transmission. The most commonly used sources are sewage, sewage, drinking water, air and germ carriers. These programs are particularly needed to monitor the abundance of clinically undetected pathogens and their potential to cause public health hazards.
Israel’s environmental monitoring program covers 15 regions across the country, including 50% of the total population. In addition, Jerusalem has four non-overlapping surveillance regions.
Detection and genome analysis of poliovirus type 2
Supplemental sewage surveillance programs have increased surveillance for acute flaccid paralysis caused by poliovirus in Israel since 1989. The presence of poliovirus type 2 was detected in April 2022 in two regions in Jerusalem and one region in central Israel.
By July 2022, the number of poliovirus type 2 detections in wastewater in the regions of Jerusalem was found to be increasing significantly. In addition, genomic sequencing of virus isolates has revealed the accumulation of mutations over time.
Two isolates of poliovirus type 2 were detected in three different regions of Jerusalem over a period of 100 days. Sequence analysis has shown that these isolates are associated with vaccine-derived poliovirus.
Five other poliovirus type 2 isolates were detected during the same period; however, these isolates are not related to the vaccine-derived virus strain. The poliovirus type 2 sequences isolated in 2022 were found to share a 2-nucleotide signature in the VP1 gene. This gene codes for the viral main capsid protein VP1.
To further identify the genetic link between isolates, whole genome sequencing was performed on isolates collected between 2020 and 2022. Results have demonstrated 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 common mutations were not present in the 2020 and 2021 sequences isolated.
Given the P2/3 genomic region, recombination with a non-poliovirus enterovirus was detected in the 3A gene. However, this recombination was absent in all poliovirus sequences isolated in 2020 and 2021.
Taken together, these observations clearly indicate a genetic link between all poliovirus type 2 sequences isolated in 2022.
Environmental monitoring in Israel has identified an increasing frequency of poliovirus type 2 isolates in various regions of Jerusalem. These isolates are genetically associated with the vaccine-derived poliovirus type 2 strain.
Vaccine-derived polioviruses originate primarily from genetically mutated oral poliovirus vaccine strains that accumulate mutations over time. A high rate of virus transmission in populations with weak immunity or a high rate of virus replication in immunocompromised patients is responsible for the emergence of vaccine-derived polioviruses.
Oral vaccination against poliovirus type 2 was stopped worldwide in April 2016 due to the emergence of vaccine-induced type 2 poliovirus-induced outbreaks. Therefore, a monovalent oral poliovirus type 2 vaccine was introduced as a prophylactic measure to control these outbreaks.
As of July 2022. Only localized transmission of poliovirus type 2 has been detected in Jerusalem. No occurrence of virus-induced acute flaccid paralysis has been observed to date. To control these outbreaks, the Israeli Ministry of Health has decided to immunize children with inactivated poliovirus vaccines.
Overall, the study underscores the importance of routine environmental surveillance in rapidly identifying outbreaks caused by vaccine-derived poliovirus and in controlling outbreaks through rapid vaccination campaigns.