Environmental monitoring of sewage conducted in Jerusalem, Israel, has detected a growing population of poliovirus type 2. Additionally, these viral isolates are associated with vaccine-derived viral strains. A detailed report was recently published in EurosurveillanceEuropean journal on surveillance, epidemiology, prevention and control of infectious diseases.
Rapid Communication: Emergence of genetically vaccine-related type 2 poliovirus in the absence of an oral polio vaccine, Jerusalem, April to July 2022. Image credit: Kateryna Kon/Shutterstock
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Environmental surveillance programs aim to detect circulating pathogens in the various sources involved in the transmission of pathogens. 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 ability to cause public health risks.
Israel’s environmental monitoring program covers 15 regions across the country, including 50% of the general population. Additionally, Jerusalem has four non-overlapping watch regions.
Detection and genomic analysis of poliovirus type 2
Additional sewage monitoring programs have increased poliovirus-related acute flaccid paralysis surveillance in Israel since 1989. Type 2 poliovirus has been detected in two areas of Jerusalem and one area in central Israel. Israel in April 2022.
In July 2022, the number of poliovirus type 2 detections in sewage was found to be sharply increasing in areas of Jerusalem. Furthermore, genomic sequencing of viral isolates showed the accumulation of mutations over time.
In three different areas of Jerusalem, two type 2 poliovirus isolates were detected over a 100-day period. Sequencing analysis revealed that these isolates are associated with vaccine-derived poliovirus.
Five other type 2 poliovirus isolates were detected during the same period; however, these isolates are not related to the vaccine-derived virus strain. Poliovirus type 2 sequences isolated in 2022 were found to share a 2-nucleotide signature in the VP1 gene. This gene codes for the main viral capsid protein VP1.
To further identify the genetic link between the isolates, whole genome sequencing was performed for isolates collected between 2020 and 2022. The results showed the presence of additional mutations in the P1 genomic region on all sequences isolated in 2022. The P1 region includes the VP1, VP2, VP3 and VP4 genes. However, these shared mutations were not present in sequences isolated in 2020 and 2021.
Considering the P2/3 genomic region, a 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 strongly identify the genetic linkage between all poliovirus type 2 sequences isolated in 2022.
Significance of the study
Environmental surveillance in Israel has detected an increasing frequency of type 2 poliovirus isolates in different areas of Jerusalem. These isolates are genetically associated with the vaccine-derived strain of poliovirus type 2.
Vaccine-derived polioviruses come primarily from genetically mutated oral poliovirus strains that accumulate the 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 the cause of vaccine-derived polioviruses.
Oral poliovirus type 2 vaccination was discontinued globally in April 2016 due to the emergence of outbreaks induced by vaccine-derived poliovirus type 2. Therefore, monovalent oral poliovirus type 2 vaccination was 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 observed so far. To control these outbreaks, the Israeli Ministry of Health decided to vaccinate children with inactivated poliovirus vaccines.
Overall, the study highlights the importance of routine environmental surveillance to quickly identify outbreaks caused by vaccine-derived polioviruses and to control outbreaks through rapid vaccination campaigns.