The emergence of COVID-19 in late 2019 as a major global pandemic is part of a pattern of disease emergence that highlights linkages among biodiversity, global environmental change and human health.
COVID-19 and other pandemics are rooted in biodiversity. They are caused by micro-organisms that are themselves a critical part of biodiversity and are hosted and transmitted by diverse animal species, including humans
- COVID-19 is the latest in a series of diseases that are caused by wildlife-origin viruses and have emerged due to anthropogenic environmental changes that bring wildlife, livestock and people into closer contact
- These diseases include SARS, Ebola and Nipah virus disease, Zika and influenza, and reflect a predominance of zoonotic (animal origin) viral diseases among the emerging infectious diseases affecting people over the last few decades.
Over the past few years, a series of scientific papers have been published that suggest the same environmental changes that threaten biodiversity loss on a global scale (e.g. land use change, such as deforestation or encroachment into wildlife habitat; climate change; unsustainable trade and consumption of wildlife; agricultural intensification; globalized trade and travel) are also driving the increasing spill over, amplification and spread of these novel viral diseases.
Relationship between people and biodiversity underpins disease
There are clear links between pandemics and biodiversity. New pathogens usually emerge from a ‘pool’ of previously undescribed, potentially zoonotic microbes that have co-evolved over millions of years with their wildlife hosts.
The diversity of microbes likely increases proportionally with the biodiversity of their hosts. RNA viruses are particularly important as emerging pathogens because they have high mutation rates, undergo recombination and have
other characteristics allowing them to evolve diverse assemblages over time 19-21.
An estimated 1.7 million viruses occur in mammals and water birds (the hosts most commonly identified as origins of novel zoonoses), and of these, 631,000-827,000 could have the ability to infect humans.
This far exceeds the current catalogued viral diversity from these hosts of less than 2,000 (even if lower estimates of viral diversity prove correct 23) and suggests that less than 0.1% of the potential zoonotic viral risk has been discovered.
Biodiversity loss: Increase transmission of microbes from animals to people:
On a global scale, the emergence of new zoonoses correlates with wildlife (mammalian) diversity, human population density and anthropogenic environmental change.
- There is also evidence that biodiversity loss may increase transmission of microbes from animals to people under certain circumstances. The potential mechanisms are complex. For some microbes with multiple reservoir host species, certain hosts may play a more important role than others, i.e. have high ‘competence’.
- This may be because they are preferentially infected, produce and excrete more microbes, have higher contact rates, or otherwise contribute more to pathogen
dynamics than low competence hosts.
- Thus, in regions with high biodiversity a “dilution effect” may exist for some pathogens, whereby highly competent reservoirs represent a small
proportion of the available reservoirs, and transmission risk to people is reduced.
Land use and climate change as drivers of pandemic risk and
Land use change is defined as the full or partial conversion of natural land to agricultural, urban and other human-dominated ecosystems, including agricultural intensification and natural resource extraction, such as timber, mining and oil. Land use and climate change are two of the five most important direct drivers of biodiversity loss, and are projected to cause significant
future threats to biodiversity and to continue driving the emergence of infectious diseases.
Changes in land use practices have benefited people through economic and social
development, but have also damaged human health, driven biodiversity loss and impaired ecosystem functions and the provision of ecosystem services.
Land use change has increased exponentially since the industrial revolution, and through a ‘Great Acceleration’ of Earth System indicators that is considered to mark the beginning of the Anthropocene.
Between 1992 and 2015, agricultural area increased by 3% (~35 million ha), mostly converted from tropical forests 124. By 2015, human use directly affected more than 70% of global, ice-free land surface: 12% converted to cropland, 37% to pasture and 22% as managed or plantation forests.
The remaining land with minimal human use consisted of 9% intact or primary forests, 7% of unforested ecosystems and 12% of rocky or barren land. With continued growth in global human population (a 30% increase from 6 billion in 1999 to 7.7 billion in 2019) and global consumption (a 70% increase in global GDP from US$84 trillion in 1999 to $142 trillion in 2019).
The trend of increased land use change is expected to continue, with potentially 1 billion ha of land cleared globally by 2050.
Way forward to reduce zoonotic diseases:
- Linkages among consumption, livestock farming, health, habitat destruction, climate change and emerging diseases have led to a number of calls for taxation to act as an incentive to reduce consumption and provide resources to tackle these negative consequences.
- These include calls for: a ‘meat tax’ on traded meat or meat products to fund zoonotic disease surveillance and
prevention from a US Institute of Medicine Committee, and analysis of taxation options;
- A tax on meat consumption to provide incentives to reduce climate change; a tax on red and processed meat to reduce the direct health consequences of meat over-consumption; and
- A review of a ‘livestock levy’ option to tackle infectious disease threats including the rise of antimicrobial resistance and climate change.
- Conservation programs that aim to conserve intact habitat, reduce land use change by sustainably managing land and reverse ecosystem degradation by restoring forest and other intact habitats may reduce the risk of disease emergence if they also reduce contact among people, livestock and wildlife.
- Restoration programs that are designed to increase wildlife movement among patches of landscape (e.g. formation of wildlife corridors), or to create ‘mosaic’ landscapes of wildlife, livestock and human communities, could increase zoonotic disease risk by increasing contact and microbial transmission among animals and people.
- This is supported by modelling studies of corridor building and forest fragmentation as well as empirical studies of fragmented habitat mosaics.
Wildlife and microbial diversity, human populations, domestic animals and landscapes are strongly interconnected, with complex dynamic feedbacks that can drive or reduce pathogen transmission.
Microbes that exploit these interactions can infect any of these populations separately, and sometimes more than one. Their emergence begins with anthropogenic drivers, and their impacts can be exacerbated by human activities.
Furthermore, reducing pandemic risks substantially through better management of environmental resources would cost 1-2 orders of magnitude less than estimates of the economic damages caused by global pandemics.