This is a paper from the research team led by Associate Professor Krista Wigginton at the University of Michigan. Wigginton’s team have focused on the fate of enveloped viruses (including coronaviruses) in the urban water cycle (drinking water, sewage, sewage treatment) for much of the last decade.
Most researchers studying viruses in water have focused on non-enveloped viruses (e.g., adenoviruses, polioviruses, enteroviruses, noroviruses and rotaviruses). This is because these are the viruses that have dominated risks associated with waterborne disease. So while risks associated with waterborne survival of enveloped viruses have been widely accepted to be lower, very little focused research has been undertaken.
In this paper, the authors examine the survival and partitioning behaviour of two model or “surrogate” enveloped viruses in raw wastewater samples:
- Murine hepatitis virus (MHV)
- Pseudomonas phage (ϕ6)
These two enveloped viruses are compared with two non-enveloped bacteriophages (MS2 and T3). This is helpful, since our current understanding of the fate of viruses in municipal wastewater is primarily based on studies with non-enveloped viruses and virus surrogates, such as these.
The work presented in this paper addresses the survival and partitioning behaviour of the two enveloped virus surrogates, in pasteurised and unpasteurised wastewater.
Inactivation of the two enveloped virus surrogates in wastewater followed first-order kinetics and was more rapid than for the non-enveloped virus surrogates.
In unpasteurised wastewater at 25 °C, the T90 values (time for 90% reduction) for MHV and ϕ6 were 13 and 7 hours, respectively, compared with 121 hours for MS2 phage. The non-enveloped T3 virus survived much longer with no significant decrease in infectivity observed within the 48 hour experiments.
Inactivation of the enveloped virus surrogates were significantly slower at 10 °C compared to 25 °C, with T90 values for MHV and ϕ6 increased to 36 and 28 hours, respectively.
Results are also presented to compare liquid–solid partitioning of the enveloped and non-enveloped virus surrogates. Up to 26% of the two enveloped virus surrogates adsorbed to the solid fraction of wastewater compared with only 6% of the two non-enveloped virus surrogates.
The authors identified that current methods to concentrate and recover non-enveloped viruses from wastewater and other environmental matrices may not be suitable for enveloped viruses. This is because lipid-envelopes are known to be sensitive to the detergents and organic solvents, commonly used to extract and purify non-enveloped enteric viruses.
Consequently, an optimised method, based on ultrafiltration, for recovering enveloped viruses from wastewater was developed and is reported in this paper. This method was shown to achieve mean recoveries of 25% and 18% for MHV and ϕ6, respectively. Higher recoveries were observed for the non-enveloped virus surrogates.
The authors state that the results presented in this paper “will be particularly important during potential future avian influenza or coronavirus outbreaks in humans, as some strains of these viruses can be excreted in faeces”. They argue that future work should examine additional enveloped viruses to elucidate the specific virus characteristics that contribute to their survival times and enhanced partitioning to solids.
Ye, Y., Ellenberg, R. M., Graham, K. E. and Wigginton, K. R. (2016) Survivability, Partitioning, and Recovery of Enveloped Viruses in Untreated Municipal Wastewater. Environ. Sci. Technol., 50(10), 5077-5085.