Description
Introduction – Objectives
Poliomyelitis is an infectious disease caused by the poliovirus which belongs to the enterovirus genus. Niger has been declared free of wild poliovirus since 2016. However, when vaccination coverage is low, and hygiene and sanitation conditions are poor, certain attenuated vaccine strains used in the past can mutate and regain virulence comparable to wild strains. This study aimed to determine the spectrum of vaccine polioviruses circulating in the environment and the seasonality of high enteroviruses detection in wastewater.
Methodology
We performed a prospective study over two years (January 1, 2022 to December 2023). Wastewater samples were collected every two weeks at the 11 open polio environmental surveillance program sites. These wastewater samples were concentrated at the National Reference Laboratory for Environmental Surveillance of Poliomyelitis using the Polyethylene Glycol 6000/Dextran method recommended by the World Health Organization (WHO). The concentrated samples were then sent to the WHO regional reference laboratory for viral culture and molecular characterization of polio enteroviruses. Samples whose results were available as of December 31, 2023, were included in this study. The analyses were conducted using the Excel 2021 tool and IBM SPSS v26 statistical software.
Results - Discussions
A total of 519 collected samples were included and tested in this study. Enteroviruses were detected in wastewater throughout the two years study. Statistical analysis revealed that the rainy season was significantly associated with detecting enteroviruses in wastewater samples (Pearson's chi-squared χ2 =40.993; df=1 and P-value=0.000<0.05). Similar results have been obtained in Pakistan, Japan, and other countries. Among all collected samples, 215 (41.42%) samples tested positive for viral culture. Seventeen (3.27%) were mutant poliovirus type 2 vaccine strains, 42 (8.09%) were original vaccine strains, and 156 (30.05%) were non-polio enteroviruses. 304 (58.57%) samples were tested negative for enterovirus detection. The original poliovirus vaccine strains were predominantly observed among poliovirus strains in the environment. This result could constitute a good indicator within the framework of the country's vaccination strategy against poliomyelitis. Only one of seventeen mutant vaccine strains of type 2 poliovirus was detected during the 2023 year. This result was the impact of the vaccination campaigns carried out in 2022 in response to case detection.
Conclusions
The detection of mutant vaccine poliovirus in the environment made it possible to alert public health authorities and trigger several vaccination campaigns to contain its spread. Environmental health authorities should carry out investigations to identify the causes of the high detection of entéroviruses in wastewater during the rainy season and then take the necessary preventive measures. This study could be extended to other enteric viruses of medical interest in wastewater to develop a better strategy to fight these infectious diseases with epidemic potential in Niger.
Keywords: Poliovirus, enterovirus, seasonality, wastewater, surveillance.
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