The insatiable virus hunter

How can human viruses found in water and air be rendered harmless? This is the research question guiding Tamar Kohn, professor of environmental science and engineering at EPFL.

A maze of buildings and corridors leads to Tamar Kohn's office at the EPFL. The scientist takes us straight to the heart of the matter and the core of her research, which can be summed up in three key words: viruses, water and air. Or four, because we have to add the coronavirus: the scientist helped to develop a method for detecting the virus in wastewater to help monitor the pandemic.

Tamar Kohn grew up in Zurich, where she went on to study environmental sciences, specialising in environmental chemistry and, more specifically, groundwater remediation. It was during her postdoc at the University of California at Berkeley that she began to take an interest in the viruses present in water. A line of research she has been pursuing at EPFL since 2007. She has just been appointed full professor.

Tamar Kohn tracks human viruses in the environment, that is to say outside their preferred habitat. "The majority of viruses found in water are enteric viruses, which come from faeces" she explains. Charming. Her job – and that of her team – is to examine all the processes involved in inactivating them. In the natural environment, this can be sunlight, heat, or grazing by microorganisms and zooplankton. In water treatment plants, these are disinfection processes using UV rays, ozone or chlorine.

She uses viruses that were isolated from wastewater and grown to high concentrations in the lab. She then exposes them to water, either in the lab, or – within safe containment, of course – in Lake Geneva and then monitors how long they continue to be infectious by testing them on various mammalian cells. These measurements can be used to model the lifespan and infectivity of viruses as a function of environmental conditions, and to determine the risk to the population. In Switzerland, as far as water is concerned, the risk is essentially linked to recreational use, e.g. via swimming because we accidentally swallow water, or fishing.

Air is her new Eldorado

For some years now, the scientist has also been tracking the fate of human viruses released into the air via aerosols, the particles we exhale through our noses or through our mouths. "This is an area of research that was little explored until 2020, but which has suddenly become very relevant with the coronavirus," notes the researcher.

One of the projects she is currently managing with support from the Swiss National Science Foundation is aimed precisely at determining how environmental conditions impact aerosols, and hence the infectivity of the respiratory viruses they contain. Although they are very heterogeneous, these particles do have certain characteristics in common, such as a low pH and the fact that they contain certain proteins. "This information will enable us to define the ideal composition of the ambient air in buildings to reduce the transmission of the influenza virus and other pathogens, such as SARS-CoV-2" says Tamar Kohn.

Most buildings could, and indeed should, be ventilated to reduce the transmission of viruses, and more attention should be paid to the composition of indoor air, the scientist insists. Removing ammonia – which is produced by humans – from indoor spaces could help, she explains, because it increases aerosol pH where a low pH is better to kill off viruses. Fortunately, people are beginning to realize this and a number of research projects are looking into the subject. We're almost seeing a "clean air revolution," she laughs.

A welcome flexibility

As well as human viruses in water and air, the researcher is also beginning to look at other types of viruses. Her new hobby: cyanophages which attack cyanobacteria, the famous blue algae. “I am interested in learning how they infect and kill cyanoacteria, i.e. how they regulate blooms or cause the release of toxins,” she explains. A new territory to conquer for the insatiable explorer. "The world of viruses is vast, and I love navigating it in search of new knowledge. I consider myself lucky to be able to do so.

Although curiosity is the driving force behind this single mother of two children aged 9 and 11, who lives in Bern, her daily life requires a good deal of organisation and sometimes a few sacrifices – she can't attend some conferences, for example. "Fortunately, my position gives me a certain amount of flexibility. But I don't have much time left outside work and my family. Just enough to clear my head by doing a bit of jogging."