Engineers at Stanford describe potential transmission pathways of COVID-19 and their implications.
Factors Affecting Covid-19 Transmission: How the SARS-CoV-2 virus that causes COVID-19, spreads across the environment is still unclear. A key reason for this is the way the virus behaves and its traits. They have high variability – some spreads through water, others through the air; some are wrapped under the envelope of fatty molecules that allow them to escape the host’s immune system, while others are “naked.”
This makes it imperative for environmental experts to work together to recognize viral and environmental features that influence soil, air and faecal transmission, according to Alexandria Boehm, a Stanford professor of civil and environmental engineering, and Krista Wigginton, the Shimizu Visiting Professor in Stanford’s department of civil and environmental engineering and an associate professor at the University of Michigan.
Boehm and Wigginton co-authored a recently published viewpoint in Environmental Science & Technology calling for a broader, long-term and more quantitative approach to understanding viruses, such as SARS-CoV-2, that are spread through the environment. They are also studying the transfer of coronaviruses between the skin surface and other materials, the effect of UV and sunlight on the coronaviruses, and the link between disease outbreaks and virus concentrations in wastewater.
According to Boehm and Wigginton, scientists and medical experts don’t have a clear idea of what virus attributes and environmental conditions influence the survival of viruses in the environment for example, in aerosols and droplets, on surfaces like skin and in water like seawater.
“When a new virus emerges and poses a risk to human health, we don’t have a good way of predicting how it will behave in the environment,” Boehm said.
Coronaviruses and most of the emerging viruses that have captured the world’s attention over the last decade are enveloped viruses that are wrapped in an outer layer of fatty lipid molecules that they’ve stolen from their hosts. Proteins present on the surface of the envelopes can help these viruses escape the immune systems of the organisms they are infecting.
“There has been much more work on the fate of non-enveloped or naked viruses because most intestinal pathogens in excrement are nonenveloped viruses – like norovirus and rotavirus,” said Wigginton.
In their paper, Boem and Wigginton address potential threats that viruses such as SARS-CoV-2 pose to water sources. We usually only worry about viruses in water if they are excreted by humans in their faeces and urine. Most enveloped viruses aren’t excreted in faeces or urine, so they aren’t usually on our minds when it comes to our water sources. There is increasing evidence that the SARS-CoV-2 viruses, or at least their genomes, are excreted in faeces. If infective viruses are excreted, then faecal exposure could be a route of transmission, according to Boehm, who added, “It’s unlikely this could be a major transmission route, but a person could potentially be exposed by interacting with water contaminated with untreated faecal matter.”
Drinking water treatment systems have numerous treatment barriers to remove the most prevalent viruses and the most difficult-to-remove viruses, according to the engineers. Research on viruses similar to the SARS-CoV-2 virus suggests they are susceptible to these treatments. “In terms of virus concentration and persistence, this isn’t a worst-case scenario,” Wigginton said.
Broadly, Wigginton and Boehm write, we tend to study viruses very intensely when there is an outbreak, but the results from one virus aren’t easy to extrapolate to other viruses that emerge years later.
“If we took a broader approach to study many kinds of viruses, we could better understand the characteristics driving their environmental fate,” Wigginton said.
The two researchers call for experts across various fields – including medicine and engineering and – to work together to move methods forward faster, make discoveries and formulate strategies that wouldn’t be possible independently.