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  • Writer's pictureDr. Polston

Environmental and human surveillance of polioviruses, VDPVs, and other enteroviruses in Madagascar

The switch from tOPV to bOPV

Poliomyelitis has been a major public health concern and currently, efforts are being made towards eradicating wild poliovirus type 2 (WPV2). A global switch from trivalent oral poliovirus vaccine (tOPV) to bivalent oral poliovirus vaccine (bOPV without PV2) has taken place in countries, like Madagascar, where epidemics of type 2 pathogenic circulating vaccine-derived polioviruses (cVDPVs) occur when low polio vaccine coverage allows the circulation and genetic drift of vaccine attenuated PV2 that can thus become pathogenic

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Madagascar has experienced several recent outbreaks (beginning in 2001 and more recently in 2015) due to cVDPVs. This is of major concern as the timeline for total eradication of polio approaches and this effort is particularly difficult in countries like Madagascar with a high population density and low socioeconomic status. Factors such as low immunization coverage and poor sanitation contribute to the circulation of polioviruses.

My project investigates the current status of circulating viruses in Madagascar, using environmental and human surveillance methods, by concurrently collecting stool samples from healthy children and environmental sewage samples before, during, and after the switch from tOPV to bOPV. The goal is to isolate and genetically characterize (using next generation sequencing) any polioviruses, cVDPVs, and enteroviruses detected in three regions of Madagascar. This type of monitoring is critical in the development of strategies aimed at eradicating polio from endemic countries.

It's all in the data

The primary purpose of the project is to monitor the occurrence of WPV2 prior to the switch and the expected disappearance of WPV2 after the switch. Based on the data collected from other countries that did similar switches, we expect to detect Sabin type 2 PV in the stool of vaccinated children as they shed the virus before the switch and potentially for a few months after the switch. However, it is expected that a decline to complete disappearance of Sabin type 2 will be observed over time because type 2 is no longer a component of the administered vaccine (bOPV). From the sewage samples collected, we expect to see similar results leading to a decline in the circulation of PV2 strain in the environment.

To confirm the successful disappearance of PV2 from the study population, we will genetically type the viruses present and perform a comparison before, during, and after the switch in the stool and sewage samples collected. The second objective of this study will be to investigate the total population of enteroviruses and other RNA viruses circulating within the three regions of Madagascar. We will compare the differences in the regional data to determine variations in circulating viruses based on geographical locations. The study’s final objective will be to evaluate the efficiency of NGS methodologies for detecting and characterizing enteroviruses isolated from infected cell lines versus those found directly in concentrated sewages.

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