European biomedical researchers show a rising interest towards parasites, often regarded as natural oddities in the past but now recognised as vital parts of natural ecosystems, in addition to having a sizable impact on human health worldwide.
Parasites are an incredibly diverse and broad group of organisms, comprising plants, animals and microscopic beings alike. Their life strategy, based on profiting from their host, makes them seem as rather undesirable creatures. This is why they are rarely talked about.
However, new research highlights not only their major impact on human health, but also their key role in ecosystem functioning.
What are parasites and why do they matter?
Parasites are generally defined as organisms that benefit from living off another organism -called “host” – without seemingly conferring a benefit in return. They can look very different from one another and even vary in the way their life cycle plays out, as some live inside the same host for all their life, while others hitchhike a few different rides.
Roundworms, tapeworms, ticks or fleas: some of them are commonly heard of. Others may sound a bit more otherworldly, like the parasitic isopods that affect fish and replace their tongues.
Altogether, some studies estimate that parasites account for about 40% of total animal biodiversity but, given their secluded nature, it is impossible to tell with certainty.
Despite these impressive numbers, parasites are rarely present in both scientific literature and general media with a few exceptions, often focused on peculiar clinical cases.
This reflects a common and widespread bias against non-humanlike creatures, especially arthropods. The consequences of what we could call “parasite blindness” can be serious, since the overall neglect towards parasite studies can ultimately end up affecting both human and ecosystemic health.
Human health concerns: the disproportionate impact on the Global South
Among the tens of thousands of parasite species that are known to science, only a few hundred can affect humans. Yet, those few species are enough to cause deeply concerning impacts on human health on a global scale. Parasitosis affect about a quarter of the global population, bringing death or lifelong consequences to millions of people.
As everything that revolves around parasites, these statistics rarely get mentioned. This has mostly to do with the fact that the highest incidence of parasitosis, by far, is in regions that belong to the so-called Global South, such as Africa, South America and South-East Asia.
Those areas are not often considered by other countries when planning research or allocating medical resources, ultimately resulting in an insufficient effort to combat said diseases.
For this very reason, most parasitosis are considered “neglected tropical diseases” by the World Health Organization. Those are a wide group of pathologies, with different causes, that produce devastating effects but are under-considered because they affect mostly impoverished communities.
Some European institutions are attempting to bridge this gap: As Dr. Marc Hübner.
Dr. Marc Hübner, Professor at University Hospital Bonn in Germany and coordinator of the cross-border eWHORM project, aimed at targeting parasitosis in sub-Saharan Africa: “Despite their impact, research in this field still receives very little funding, leaving millions to suffer, hence the name “neglected”. It’s just unbelievable and it is not public enough. We are currently working on a basket trial in which we hope to provide proof of concept of oxfendazole as a pan-nematode drug candidate. If this works, it will be a huge advancement in the treatment of such diseases. Collaboration is key, so we are working closely with our African partners.” – Read the full interview with Marc Hübner
The project is ongoingand it is too early to tell whether the new molecule is effective, although there are some promising signs. The simple fact that this research effort is being funded and that it is produced in strict collaboration with the affected Nations, is a great result.
Looking at the future, Dr. Hübner explains how it is unlikely that parasitosis, especially the ones he works with, will make their way to Europe. Still, climate change will make the situation worse in the areas where they are already present and will facilitate the spread of pathologies with different causes but similar dynamics (ex. viruses spread by mosquito vectors) at northern latitudes.
Positive effects of parasites
The fact that some parasites negatively impact human health leads us to think that all parasites must have a similarly harmful role, regardless of their host. Surprisingly enough though, that is not the case. A lot of wildlife parasites have neutral effects on their hosts or mediate important ecological interactions, that result in positive outcomes for the whole ecosystem.
In the wild, most animals are infected by at least some parasites, but only a few individuals host so many that they die or become seriously ill. Even in those scenarios parasitism, if fatal for a single individual, can be positive on an ecosystemic level: fish for example, wheninfected with eye parasites, have a reduced eyesight which in turn facilitates the hunt of delicate aquatic birds like herons.
One well-documented case relates to the endangered Kirikuchi char, which is endemic to the Kii Peninsula in Japan. Those fish base around 60% of their diet on insects that jump into the Totsu river system, where the chars liveThese insects actively dive into the water, because their nervous system is controlled by parasitic horsehair worms. Hence those worms, while damaging to a small part of the local insect population, are salvific for the endangered fish.
New research at the European level is trying to dig deeper into the roles of parasites in conservation and how they may be considered when planning biodiversity monitoring.
Dr. Rachel Paterson, researcher at the Norwegian Institute for Nature Research and lead of the EU-funded IMPACT project (Integrated Monitoring of Parasites in Changing environments), focused on parasite monitoring in freshwater environments: “Parasites are one of the most neglected groups of organisms when it comes to conservation priorities. One of our goals in IMPACT is to develop tools to integrate parasites into biodiversity monitoring. A promising opportunity comes from the field of eDNA (environmental DNA), the analysis of DNA fragments found in environmental samples, which is commonly used in freshwater environments to monitor fish or invertebrates. However, to track the presence of any given species using eDNA, one must know how to genetically identify the species (so called “genetic references”). Thus, we are building this necessary information for aquatic parasites. We also work closely with stakeholders and policy makers, to understand what barriers are preventing them from considering parasites in conservation policies.” – Read the full interview with Rachel Paterson
Another member of the IMPACT group, Dr. Isabel Blasco-Costa, once defined parasites as “puppet masters”, that stay hidden and pull the strings of ecosystem functioning. Gathering more knowledge on this subject is not only crucial for nature’s conservation: As we know, in a One Health framework, our health is inextricably linked to that of natural ecosystems. Thus, if parasites are so crucial for ecosystemic well-being, they are important for us as well.
We need to know more, do more
Exploring the diversity of parasites, learning how to fight the few species that are pathogenic to us and how to protect the ones that help our planet thrive. Researchers like Dr. Hübner and Dr. Paterson are trying to do just that.
Their findings, both present and upcoming, challenge the mainstream idea that we have of parasites and of nature in general. They invite us to overcome our biases and look at distant organisms with a new perspective.
Only with the right public support and interests, these projects – and others like them – can continue to shape our future and shed light on neglected aspects of our present. In the context of the global climatic and biodiversity crisis that we are facing, part of the solution lies in the study of the most disliked beings.
Related content:
• A scientist’s opinion: interview with Dr Marc Hübner on the importance of parasite research
• A scientist’s opinion: interview with Dr Rachel Paterson on the importance of parasite research