Detection of the SARS-CoV-2 Delta Variant in the Transboundary Rivers of Yunnan, China

Ruili and Longchuan, two border counties in southwestern China, are facing epidemic control challenges due to the high rate of COVID-19 infections originating from neighboring Myanmar. Here, we aimed to establish the applicability of wastewater and environmental water surveillance of SARS-CoV-2 and conduct whole-genome sequencing (WGS) to trace the possible infection origin. In August 2021, total 72 wastewater and river water samples were collected from 32 sampling sites. SARS-CoV-2 ORF1ab and N genes were measured by RT-qPCR. We found that 19 samples (26.39%) were positive, and the viral loads of ORF1ab and N genes were 6.62 × 10²-2.55×10⁵and 1.86 × 10³-2.32 × 10⁵copies/L, respectively. WGS further indicated the sequences in two transboundary river samples, and one hospital wastewater sample belonged to the delta variant, suggesting that the infection source might be areas with high COVID-19 delta variant incidence in Southeast Asia (e.g., Myanmar). We reported for the first time the detection and quantification of SARS-CoV-2 RNA in the transboundary rivers of Myanmar-China. Our findings demonstrate that wastewater and environmental water may provide independent and nonintrusive surveillance points to monitor the global spread of emerging COVID-19 variants of concern, particularly in high-risk regions or border areas with considerable epidemic challenges and poor wastewater treatment facilities.