Getting sick from COVID-19 is a terrifying thought for millions of Americans and people around the world. However, how the virus spreads though a population is not yet understood. Researchers at Stanford are studying how this virus can be transmitted, and possible sources of environmental transmission.
Much remains unknown about how SARS-CoV-2, the virus that causes COVID-19. While microbiologists study the effects of the virus inside the body, engineers at Stanford are interested in understanding how this virus travels through communities.
A major reason why this information is not yet known is that the behaviors and traits of viruses are highly variable. While some spread more easily through water, others travel through the air; some are wrapped in layers of fatty molecules that help them avoid their host’s immune system, while others still are “naked” and able to destroy the host immune system.
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, worked together on a study to explain why it is an urgent matter for environmental engineers and scientists to collaborate on pinpointing viral and environmental characteristics that affect COVID-19 transmission via surfaces, the air, and fecal matter.
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 how they are spread through the environment. They are also principal investigators on a recently announced National Science Foundation-funded project to study the transfer of coronaviruses between skin and various materials, the effect of UV and sunlight on the coronaviruses, and the connection between disease outbreaks and virus concentrations in wastewater.
They are concerned that scientists and medical experts do not yet have a comprehensive understanding of what virus characteristics and environmental factors influence virus persistence in the environment, in the form of aerosols and droplets, surfaces including skin, and water including 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.
One reason for this lack of understanding is historically there has been limited funding for this sort of work. The National Institutes of Health historically hasn’t funded work on pathogens in the environment, and funding at the National Science Foundation for this research is limited. Additionally, coronaviruses and most emerging viruses that have caught the world’s attention over the last decade are enveloped viruses that are wrapped in an outer layer of fatty lipid molecules that has been taken from the virus’ host. Proteins that line the surface of these envelopes assist these viruses in evading the host 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. They explain how people usually only worry about viruses in water if they are excreted by humans in their feces and urine. Most enveloped viruses aren’t excreted in feces or urine, so they aren’t usually on our minds when it comes to our water sources. There is increasing evidence that SARS-CoV-2 viruses, or at least their genomes, are excreted in feces. If infective viruses are excreted, then fecal 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 fecal matter.”
Drinking water treatment systems have numerous treatment barriers to remove the most prevalent and difficult-to-remove viruses, according to waste water engineers. Research on viruses similar to SARS-CoV-2 suggests this virus type is susceptible to these treatments. “In terms of virus concentration and persistence, this isn’t a worst-case scenario,” Wigginton said.
Wigginton and Boehm further claim that 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 studying many kinds of viruses, we could better understand the characteristics driving their environmental fate,” Wigginton said. This will make it possible to create predictive models based on the underlying mechanisms controlling the persistence of enveloped viruses, and may reduce the need to study every virus under every condition.
The two researchers call for experts across various fields—including medicine and engineering—to work together to move methods forward faster, so they can make discoveries and formulate strategies that wouldn’t be possible independently.
