Biodiversity
Loss of Ecosystems and Outbreak of Diseases

There is much to suggest that the loss of biodiversity in ecosystems could have a direct influence on the emergence of diseases such as COVID-19. Part of the solution is to learn and to implement sustainable practices at both the meta and micro levels.

By María Toledo-Garibaldi

We humans are destroying ecosystems at an alarming rate. As biodiversity is lost, so too are we losing the so-called ecosystem services, that is to say the many ways in which nature supports human life. These include reducing air pollution, regulating temperature, filtering and purifying water and pollinating plants. In addition to the loss of these services, deforestation and marine pollution could have further negative and direct effects on human life, such as the outbreak of infectious diseases.

Most ecosystems are home to viruses, bacteria, fungi and parasites that can cause diseases in humans. However, this does not mean that natural environments necessarily pose a risk to humans as a source of infection. On the contrary, a healthy ecosystem, such as a forest that has not been changed radically by humans, will have developed “defence systems” against most of the microorganisms that live there. An ecosystem with considerable biodiversity is more resistant to the effects of microbial pathogens because it is more likely that some life forms within the ecosystem will have already become immune to certain diseases. In a healthy ecosystem, the disappearance of one resistant species is followed by a new one that takes its place. But what happens in the opposite scenario – in an unhealthy, damaged or destroyed ecosystem?

If an ecosystem is not healthy, be it as a result of a loss of biodiversity or habitat, a change in land use, contamination, or invasion by exotic species, such biotopes and the species that live within them will probably be more susceptible to pathogens.

More than two million people died from zoonotic diseases

Disease has always been a part of human history. However, I have the impression that we are seeing more and more pathogens that pose a risk to humans, and that they cause diseases that occur ever more frequently. This impression has prompted some scientists like Kate Jones from the University College London or Andrew P. Dobson from Princeton University to theorize that there may be a link between the destruction of ecosystems and their biodiversity and the emergence of new pathogens.

Teams of vets, conservation biologists and ecologists are trying to understand the correlation between the agricultural use of nature by humans and the occurrence of infectious diseases. For example, the EcoHealth Alliance has developed several projects that aim to protect nature in vital ecosystems with a view to preventing infectious diseases. During the course of the “Predict” project, around 140,000 samples were collected from high-risk species of wild animals in Bangladesh, Ivory Coast, the Democratic Republic of Congo, China, Egypt, India, Indonesia, Jordan, Liberia, Malaysia and Thailand. The aim was to create a virus database that could be used to identify the virus responsible in the event of human infection. Another project is studying ecosystems from the perspective of wild animal and plant protection so as to prevent microbial pathogens from leaving forests in hosts such as humans and thereby reaching nearby settlements – and then possibly triggering the next pandemic.  

Malaria, Zika, dengue, chikungunya and yellow fever are mosquito-borne diseases that are associated particularly with deforestation in subtropical regions. Recently cleared areas offer a combination of sunlight, water and warm temperatures, creating the ideal breeding conditions for the mosquitoes that carry the diseases. In turn, this poses a danger for nearby populations. It was shown by a 2009 study, for example, that deforestation in the Peruvian Amazon and the resulting ecological damage caused Anopheles darlingi larvae – which carry the malaria pathogen – to settle, increasing the malaria risk for human populations in the region. A sharp rise in malaria cases was also recorded on the island of Borneo following rapid deforestation for palm oil plantations.  

Furthermore, the International Livestock Research Institute reported as early as 2012 that more than two million people around the world had died of zoonotic diseases, i.e. those transmitted to humans by animals, such as AIDS, Ebola and the Nipah virus.

Covid-19 also transmitted by animal?

HIV, for example, jumped species when it spread from chimpanzees to humans. According to the most common theory, hunters contracted the virus after killing primates and eating their meat. The HIV pathogen, which can potentially cause the immune deficiency syndrome AIDS, is currently carried by some 38 million humans around the world. Ebola may also have been transmitted to the human population through close contact with the organs, blood and secretions of infected animals, such as fruit bats, chimpanzees, gorillas, apes, antelopes or porcupines. The Nipah virus, which frequently causes meningitis, was first isolated in Malaysia in 1999. It is assumed that it spread from fruit bats to pigs, and then from pigs to humans.

Scientists still do not know how humans first became infected with the novel coronavirus SARS-COV2 that causes the disease COVID-19. Studies have arrived at two main theories about the origin of the virus. One is that it was passed to humans from bats by an animal host, as there are no documented cases of direct transmission from bats to humans. According to the second theory, the virus may have been transmitted directly to humans but went unnoticed for a time, allowing it to spread while ultimately evolving into its current pathogenic form, within which it is further mutating. According to this theory, coronavirus may have been passed from a pangolin to a human.

We are responsible for a healthy ecosystem

These examples are intended to make it clear that the occurrence of diseases caused by microbial pathogens may have been facilitated by the way humans treat nature and by the resulting environmental problems. Although this is still controversial within the scientific community, the aforementioned research studies do point to a link. The exploitation of natural resources, including urbanization, deforestation, agricultural development, mining and trade in wild animals, has led to a loss of biodiversity that is being exacerbated by climate change.

The solution is not simply to make sure that ecosystems remain intact without any human intervention, as this is impossible. One response to the growing environmental problems that are affecting us to an ever greater extent would be to learn and to implement sustainable and viable practices at both the meta and micro levels. It is important to understand that there is a direct link between the health of ecosystems and the health and wellbeing of humans. It is our responsibility to keep the planet healthy so as to ensure our survival as well as that of all other species.