For weeks now, the corona pandemic has had the world holding its breath. It is believed that the potentially life-threatening virus was transmitted from animals to humans at a fish market in the Chinese city of Wuhan. Simone Sommer, a professor at Ulm University, is an expert on this kind of disease, known as “zoonoses” in her field. In an interview, the director of the Institute of Evolutionary Ecology and Conservation Genomics explains what needs to happen in order for pathogens to cross the species barrier and addresses the roles of environmental destruction and wild animal consumption.
Professor Sommer, the novel coronavirus SARS-CoV2 is said to be a zoonosis, i.e. an infectious disease that is found both in humans and in animals. What needs to happen in order for a pathogen to transcend the species barrier?
Sommer: “In a general sense, we can say that viruses have structures on their surfaces that fit like a key into the lock of a host cell. Only viruses with the matching key can penetrate the cells of a new host and re-programme them to produce replicates of the virus. However, it can happen that the host cell makes a mistake in replication, causing the virus to mutate. This can result in the accidental creation of a key that fits the cells of a completely different host species.
To put it in more concrete terms: if a virus crosses over to humans from the original animal host, there could be one pathogen out of millions that is actually able to infect human cells. When this happens, the species barrier is transcended, an animal infection is passed on to humans and it begins to spread. This is most likely what happened at the market in the Chinese city of Wuhan. At this point, it is not yet clear whether the transmission occurred directly from the bat to humans or whether another species was involved”.
As was the case with Ebola, for instance, the origin of the corona pandemic appears to be a bat. Why do these animals repeatedly trigger epidemics?
“First of all, I need to put in a good word for bats. They are extremely important for the functionality of our ecosystems and play a major role in plant pollination, for example.
One factor that repeatedly causes bats to become the starting point for a disease is undoubtedly the high species diversity: of the approximate 5500 species of mammals, more than 1400 of them are bats. Another group of animals with high species diversity is rodents, and there you find a large number of potentially dangerous pathogens as well – ranging from the hantavirus to bacteria that can cause the plague. A large number of differing species naturally ensures that there are also many pathogens, such as bacteria and viruses, associated with them.
But there are other factors that make bats good hosts for pathogens as well. They often live in large groups and are therefore particularly at risk of becoming infected with pathogens from fellow members of their species. Bats are also highly mobile and can transport pathogens from one colony to another. From the perspective of a pathogen, this is obviously ideal”.
What distinguishes the novel coronavirus, SARS-CoV-2, from the related SARS pathogens? The SARS pandemic in 2002 and 2003 brought significantly fewer deaths.
“The major difference is that SARS-CoV-2 replicates in the cells of the upper respiratory tract - so in the back of the throat - at the start of the infection. During this phase, symptoms may be very mild. Humans can infect other humans without even knowing that they are infected themselves”.
Ebola, swine flu, SARS, MERS …it seems that the number of diseases that are crossing over from animals to humans is increasing. Is this an accurate perception? What is the reason for this?
“It appears that this is the case. The earth has apparently reached many tipping points. Environmental destruction, increasing population density, globalisation and a drastically increasing probability of contact among different species all create favourable conditions for the development of zoonotic diseases. We also need to consider that new technologies are making it easier to detect new diseases, and that cases are now being reported much faster and in greater detail”.
What can humans do to prevent further zoonotic diseases?
“Scientific studies show that zoonotic diseases are connected to environmental destruction and the consumption of meat from wild animals. In particular, changes in land use seem to increase the risk of such diseases developing. Around 70 per cent of the newly emerging infectious diseases that affect humans are in fact zoonoses, i.e. they originate from animals.
It used to be that humans and animals lived together peacefully with a whole range of pathogens, to which they had adapted throughout the course of their evolution. But now, disrupted environmental conditions are opening up new possibilities of transmission for viruses and the like. Species communities are changing, vulnerable species are disappearing and diversity is diminishing. At the same time, so-called generalists are occupying the ecological niches that have become available and are proliferating rapidly. Unfortunately, the same applies to their pathogens. As the genetic material of viruses mutates especially quickly, these pathogens have the potential to eventually spread to the cells of a new host species. Anthropogenic changes in land use bring species into contact that would never have met under natural conditions.
In addition to the destruction of nature, further sources of zoonotic diseases include the aforementioned trade with wild animals and the consumption of meat from wild animals, also known as bushmeat in African countries.
Let us hope that we learn one thing through the adverse effects of the current corona crisis: species, environmental and even climate protection need to be given higher priority – if for nothing else, than for our own health”.
The fish market in Wuhan is considered to be the source of the novel coronavirus. How could the virus have transcended the species barrier in this specific case?
“Everything points to the Huanan wet market in Wuhan being the source of the corona pandemic. This is where species that don’t have any contact in nature come together. Up to 40 different species of farm and wild animals were traded in tight quarters and slaughtered on site.
Here, the novel coronavirus seems to have crossed the species barrier. As I stated earlier, it is assumed that a bat was the origin of the pandemic. It has not yet been determined if there was a medium host in the crossover to humans”.
Were you surprised to learn of the outbreak of the corona pandemic?
“Scientists have been warning for some time already that something like the SARS pandemic could repeat itself. However, the speed with which it spread and the extent of the health, social and economic impacts definitely surprised us all. No one suspected something like this. Imagine if someone had made a movie about a scenario like this back in October of 2019. The general response would have been ‘typical Hollywood’. On a side note, I think that the intervention measures in Germany, such as the ban on contact and the restrictions on leaving homes, were the right thing to do”.
Long before zoonotic diseases such as SARS-CoV2 dominated the headlines, you were conducting research in this field. How did you end up in this field of research?
“I worked in Madagascar for a long time. There, I was able to observe how forests were being destroyed from year to year, decreasing the habitat for endangered species and with it their population sizes. While I was working on my PhD, I was interested in the impact that this environmental destruction had on the immunogenetic diversity of animals and thus their defence mechanisms against pathogens.
These research results laid the foundation for large-scale studies spanning several years in southern Africa, Brazil and currently in Panama. In several different types of geographical areas that are affected by humans to different degrees, we are investigating the effects that changes in land use and destruction of ecosystems have on the health of wild animals”.
How do you run your projects on zoonotic diseases in the field and in the lab? What are the most important questions you ask?
“We do most of our work in the tropics, because wilderness regions with a high species diversity offer ideal conditions for conducting these kinds of studies. Parasites and pathogens like viruses and bacteria are present there in a large numbers as well. The main question we ask is: How does the health of wild animals differ within the same ecosystem in various environments that are disrupted to different degrees of intensity? We are also researching the mechanisms that promote the development of zoonotic diseases.
On the one hand, our research focuses on individual resistance to pathogens – expressed by the diversity of immune genes. Here we are also increasingly looking at the intestinal microbiome in animals, which interacts closely with the immune system.
On the other hand, we are also investigating the impact of habitat changes on the occurrence and infectivity of pathogens – from viruses, bacteria and fungal infections to single-cell organisms and worms that attack the gastrointestinal tract.
Here in Um, I have a great conservation genomics lab, where we use high-throughput sequencing to analyse the samples we collect in the tropics. We use bioinformatic and statistical methods to evaluate the data on the genetic diversity and health status of the animals. The basis for our lab analysis is the interdisciplinary “one health” concept, with its roots in ecology as well as human and veterinary medicine. According to this idea, human, animal and environmental health are all closely related. On a side note, we are working together with Christian Drosten from the Charité Hospital to identify viruses”.
To what extent does your research help virologists who are currently looking for a Covid-19 vaccine or effective medication?
“It is not our aim to develop a vaccine or an effective medication. That is a job for doctors, immunologists and biochemists.
Our research sets in one step earlier. We contribute to an understanding of the mechanisms that can lead to the development of zoonotic diseases, which threaten the health of wild animals, farm animals and ultimately human beings”.
About Prof Sommer:
Prof Dr Simone Sommer (born in 1967) studied biology in Heidelberg and Tübingen, where she also completed her PhD on the population ecology and immunogenetics of the Malagasy giant rat. After spending time in Hamburg (acquiring her ‘habilitation’ – a German postdoctoral lecturing qualification), Potsdam and Berlin, she became the director of the Institute of Evolutionary Ecology and Conservation Genomics at Ulm University in 2014. As part of her research approach “EcoHealth”, she investigates the interaction of animal, environmental and human health. She also researches zoonoses – infectious diseases that affect animals and humans. Simone Sommer’s research is not restricted to a specific species nor to a specific type of landscape. Research stays have led her to places like Madagascar, the USA, Brazil, Namibia and South Africa, and repeatedly to Panama, where she works at the Smithsonian Tropical Research Institute on Barro Colorado Island.
Interview and Media contact: Annika Bingmann