Spatial and temporal distribution of enteric viruses in wastewater and surface water

Abstract

Waterborne diseases, especially infectious diarrhoea, remain a public health concern particularly in developing countries where many lack access to safe clean water. The quality of water is assessed using bacterial indicators. However, they may not fully imitate the threat from other non-bacterial pathogens like enteric viruses. The aim of the study was to ascertain and establish the viral load, the seasonal and spatial distribution of rotavirus and norovirus (GI and GII) in sewage and river water samples. A total of 59 samples of raw and treated sewage as well as surface water, were collected from a sludge activated wastewater treatment plant in Gaborone, and Notwane River. Viruses were recovered from water samples and concentrated using the Polyethylene glycol/NaCl precipitation. The detection of enteric viruses was performed using molecular analysis (real-time RT-PCR) in concentrated water samples collected over a period of 12 months from November 2015 to October 2016. The enteric viruses were detected throughout the study period except for norovirus GI, which was not detected in June. Rotavirus was the most prevalent and was detected throughout the study period with the highest number of positive samples (76.3%), followed by norovirus GII (42.4%) and norovirus GI (38.9%). Norovirus GI had the highest number of positive samples in May (where all the samples collected were positive), followed by December and February. The enteric viruses were detected in all the study sites. Norovirus GI was mostly detected in S1 (inlet), followed by S5 (Notwane river in Matebele). Detection rate in S2 (secondary settling tank), S3 (maturation ponds) and S4 (Notwane river in Oodi) was almost the same. Similarly norovirus GII was mostly detected in S1 followed by S4. Sites S2, S3 and S5 had same detection rates. Rotavirus was the most prevalent with the highest detection in all the sites. S1 and S2 recorded the highest number of positive samples, whereas S3, S4 and S5 had the same numbers. The viral loads were still high after the treatment process. There was no significant association between physicochemical parameters and viral loads, except for pH which had a significant relationship with rotavirus and norovirus GII (p = 0.05). This study enhances an understanding of the occurrence and quantification of the enteric viruses in wastewater before and after treatment, which is important to guide policy makers in devising relevant interventions that could determine disinfectant dose and ensure sanitary safety levels of treated water.