Connecting disease research in plants, animals and humans

Research into infectious diseases in plants, animals, and humans typically occurs in ‘silos.’ Researchers often focus on one species and one pathogen per project. The new global PADDLE platform (Plant & Animal Diversity-Disease Relationships across Levels of Ecology), an initiative by Wageningen scientists Liesje Mommer and Kevin Matson, bridges academic fields. Its first tangible result is a workable scientific model.

Liesje Mommer, professor of Belowground Ecology, considers the soil beneath our feet a treasure trove where she repeatedly makes new discoveries. Experiments in recent years have confirmed that biodiversity is crucial for a healthy, functioning ecosystem. It promotes crop productivity and makes the soil more resistant to drought.

According to Mommer, there is a clear relationship between the number of organisms in an ecosystem and the risk of diseases. The rule is: the more species, the lower the chance of diseases. But according to her, it’s not just about numbers; the properties of plants and animals and their interactions also matter. ″Due to a deadly disease that nearly wiped out the rabbits, large grazers, including the European bison, were introduced in the dunes. The logic was: shorter grass leads to fewer tick bites. But the bison carries a different type of tick that is new to the dune landscape and can make dogs very sick. When it comes to disease pressure, a bison is not the same as a rabbit, even though they both keep the grass short.″

Another Language

To learn more about the underlying mechanisms, she contacted Kevin Matson, who, as an associate professor, focuses on animal physiology, animal ecology, and immunology. Together, they discovered that plant scientists speak a different language than animal scientists. Mommer: ″I had trouble understanding that language. Although I see the same patterns, different words are used on both sides of the spectrum for the same things, and the same words for different things. While it is so important to understand each other.″

Matson shares her opinion: ″In animal sciences, not much attention is paid to the plant world for inspiration and connection. The mismatch in terminology doesn’t help. Additionally, research often focuses on one scale, for example, one disease in one bird species. Researchers tend to stay in their own niche.″

International Workshops

Mommer and Matson saw that they could learn a lot together, both in terms of terminology and concepts. For example, about the contagiousness and transmissibility of pathogens and the relationship with characteristics such as body size, immune system, and defense mechanisms.

The ERRAZE@WUR programme of Wageningen University & Research honoured her project proposal for the development of a platform to bridge disciplines. This platform was named PADDLE, short for Plant & Animal Diversity-Disease Relationships across Levels of Ecology. What followed was a series of international workshops with leading scientists from the plant and animal worlds. Experts in human health also joined. Mommer: ″We deliberately invited a wide diversity of people, from professors to master’s students. That diversity seemed important to us to really make progress.″

‘Aha Moment’

The workshops alternately took place on-site and online. The goal was to develop a scientific model for researching the relationship between biodiversity and disease risk that scientists from different disciplines can work with. Using visual design techniques, the input was distilled into a cube model (see figure). Mommer: ″The workshops really helped us break free from our habits. It also helped change the way we think about diseases. With this new model, we have taken a big step. It bridges the gap between disciplines. For us, it was truly a big ‘aha moment.’″

Matson adds that the model also makes it clear that there are multiple research directions to pursue: ″It shows that you don’t have to stay in your own, familiar box, but that you can explore perhaps five research directions. He presented the model at the symposium of the Society of Integrative and Comparative Biology to a broad group of scientists. Colleagues were enthusiastic about the model, and hopefully, a shared conceptual model will have a snowball effect.″

Figure. Plant and Animal Diversity and Disease across Levels in Ecology (PADDLE) Model.  In this model, the Host Quality, the contribution of a host species to the fitness of a parasite species, is key. Exposure: probability of contact between a host and infectious parasite propagules. Establishment: probability that the parasite infects a host, given contact has occurred. Growth: parasite growth and persistence in an infected host. Infectivity: release of infectious propagules from an infected host that are accessible to susceptible hosts. By Mommer and PADDLE team.

Figure. Plant and Animal Diversity and Disease across Levels in Ecology (PADDLE) Model. In this model, the Host Quality, the contribution of a host species to the fitness of a parasite species, is key. Exposure: probability of contact between a host and infectious parasite propagules. Establishment: probability that the parasite infects a host, given contact has occurred. Growth: parasite growth and persistence in an infected host. Infectivity: release of infectious propagules from an infected host that are accessible to susceptible hosts. By Mommer and PADDLE team.

He looks back on a successful series of workshops. ″We always had good discussions, even during the online workshops. As scientists, we still realise too little how much it yields when you truly collaborate beyond the boundaries of your own discipline.″

Ecosystem Approach

The key question: will this model contribute to a more effective approach to disease prevention in plants and animals? Mommer thinks so: ″We are increasingly realising that we should not focus on a subsystem, but that we need to choose an ecosystem approach. That means focusing on the entire ecosystem, rather than just one pathogen or host. This model helps us describe all types of interactions. It is no coincidence that policymakers from the RIVM have asked us to make this model public. It helps further the discussion about the risks you run when intervening in ecological systems. The health of plants and animals ultimately also affects humans.″

She points to the risk of monocultures in agriculture and the intensive use of pesticides: ″Monocultures are intrinsically susceptible to pathogens. That can and must be different if you can use biodiversity in the field and landscape to reduce the chance of diseases.″

″Thinking Differently About Diseases″

Joukje Siebenga, manager of the ERRAZE@WUR research and investment programme, decided to honour Mommer and Matson’s funding request: ″I am extremely proud of this project, precisely because it develops conceptual knowledge. It will help us create landscapes that are safer for plants, animals, and humans. The findings in PADDLE underpin the notion that we need to think differently about diseases. Where we have always been inclined to eliminate every risk, this interdisciplinary collaboration teaches us that we should really use the strength of the landscape and of animals to minimise risks.″