HIV, Ebola, SARS, avian influenza, and now COVID-19 are amongst a number of viruses that all share one factor in common: they are all animal-borne. This means they originate from wildlife or livestock before being transmitted to humans. Animal-borne diseases are known as zoonotic diseases (or zoonoses), and they account for 60 per cent of known infectious diseases. The emergence of COVID-19 and other novel viruses are on the rise. According to the U.S. Centres for Disease Control and Prevention (CDC) an estimated 75 per cent of new and emerging infectious diseases are zoonotic in origin. New diseases are appearing from biodiversity “hotspots” such as tropical rainforests or bushmeat markets in African and Asian cities. The exploitation of the environment and wildlife has facilitated the conditions for the coronavirus pandemic to emerge.
Pathogens transfer from animal species into human hosts through a process called “zoonotic spillover.” A new study, published by The Royal Society, has concluded that the highest spillover risk comes from threatened and endangered species whose populations have largely declined as a result of hunting, wildlife trade and habitat loss. Spillover is being driven by environmental degradation as people are encroaching natural habitats and disrupting ecosystems which leads to increased human contact with wildlife.
Human behaviour and our relationship with nature – our ecological footprint – has enabled conditions for pathogens to spread. A disease ecologist, Thomas Gillespie, argues that people have created the conditions for viruses to jump species by removing the natural barriers between host animals and humans. Like its precursor SARS, COVID-19 is thought to have originated from wildlife sold for consumption at a ”wet market” in Wuhan, China in early December last year. The virus may have stemmed from a bat before it “spilled” from its natural environment into an intermediary host like a pangolin and then infected people – although this link has not been officially established. However, what is becoming increasingly clear is the connection between the COVID-19 crisis and biodiversity loss.
The United Nations Environment Programme (UNEP) has highlighted the ways in which environmental degradation makes the emergence of zoonosis more likely. Drivers of disease include deforestation, intensive farming, the illegal and poorly regulated wildlife trade, antimicrobial resistance, and climate change. Deforestation and land use changes heighten the risk of zoonosis as they displace species, leading to increased contact between wildlife and people. For instance, the Ebola outbreak in West Africa resulted from forest loss, which brought wildlife like bats closer to human settlements. The destruction of pristine forests is often driven by logging, mining, and the expansion of agriculture which are fuelled by rapid urbanization and population growth. The intensification of agricultural activity has been linked to the emergence of bird flu in intensive poultry farming.
Along with habitat loss, climate change is causing the migration of wildlife to new locations, resulting in new species interactions. This further increases the risk of new diseases emerging. For instance, mosquitoes that transmit Zika and dengue fever are migrating from the tropics into new regions where they were not previously found. Environmental and climatic pressures are affecting ecosystem integrity (their structure and function) which can alter animal behaviour and reduce biodiversity, leading to pathogens exploiting new hosts.
Pathogens naturally circulate within animals and are shed when environments are disturbed; they look for new susceptible hosts which are often humans. It is often bats, rats, and mosquitoes that remain in degraded environments, and thus they are usually the species that transmit zoonotic diseases to people. Ecosystem integrity and biodiversity can help regulate diseases and prevent pathogen spillover.
Wildlife trade and trafficking is also often linked to illegal logging and forest clearing, further facilitating the risk of human exposure to new infectious diseases. Wild animals are being poached and hunted; some of these species are near extinction and sold in markets. This trade is fuelled by a growing demand for animals for food, traditional medicines, and as pets.
More animals than ever are being transported globally and held in markets, in close proximity to other animals and to humans. Markets are a major source of new viruses because animals are particularly vulnerable to infection as they are stressed and immunocompromised. Thomas Gillespie believes that “Wet markets make a perfect storm for cross-species transmission of pathogens. Whenever you have novel interactions with a range of species in one place, whether that is in a natural environment like a forest or a wet market, you can have a spillover event.”
China is a major destination and consumer of the wildlife trade. Under the Convention on International Trade in Endangered Species (CITES), the trade of endangered species is prohibited. However, weak enforcement and the demand for meat and animal products used in traditional Chinese medicine hinders the control of the trade and conservation efforts. In response to the coronavirus outbreak, Chinese authorities have shut wildlife markets since February and banned the trading and consumption of wild animals.
Conservationists and the United Nations’ Biodiversity Chief have called for a permanent global ban of wildlife markets and improved trade regulations to prevent future pandemics. Elizabeth Maruma Mrema, the Acting Executive Secretary of the UN Convention on Biological Diversity, emphasized that a ban must consider communities – particularly in low-income rural areas – which are dependent on wild animals to sustain their livelihoods. Alternatives must be provided; otherwise, there is a risk of opening up an illegal trade in wild animals.
Improved monitoring and enforcement of illegal trafficking and the poaching of wildlife will help prevent the spread of disease whilst addressing a major component of species extinction and biodiversity loss. A ban on ”wet markets” will help mitigate the threat of future pandemics. However, a more holistic approach will be required for prevention, including protecting ecosystems and biodiversity.
Undermining the health of the environment ultimately compromises public health as well. This is reiterated by Kate Jones, the Chair of Ecology and Biodiversity at UCL, who cited emerging zoonoses as an “increasing and very significant threat to global health, security and economies.”
The coronavirus pandemic provides the world with an unparalleled opportunity to reimagine our relationship with our environment and society, shaping a more sustainable future. Planetary Health is a new discipline which provides a more holistic approach; it highlights the connection between human well-being and the well-being of all living things and entire ecosystems. Health and environmental policy must be intertwined. However, decision-making rarely considers how resource use and development impact ecosystems, such as land clearing, energy and transport infrastructure, and industrial farming.
The role of biodiversity and conservation in disease prevention has received increased attention. In a review of biodiversity and human health by the UN, scientists wrote that “an ecological approach to disease, rather than a simplistic ‘one germ, one disease’ approach, will provide a richer understanding of disease-related outcomes.” Preventing habitat loss can help maintain biodiversity and reduce the conditions which cause zoonosis. Community-based forest conservation and sustainable agriculture are both vital to ensure healthy ecosystems and communities.