The coronavirus (COVID-19) is a zoonotic disease. Zoonotic diseases are transmitted between animals and humans. Diseases passed from animals to humans are a significant threat to human health. When the symptoms are serious, our lack of prior exposure means humans have no existing antibodies to defend themselves against the disease. Recent zoonotic disease outbreaks include Severe Acute Respiratory Syndrome or SARS (2002); Avian Influenza or bird flu (2004); H1N1 or Swine Flu (2009); Middle East Respiratory Syndrome or MERS (2012); Ebola (2014– 2015); Zika virus (2015–2016); and the West Nile virus (2019).
Almost a century’s worth of global trends confirm that zoonotic disease outbreaks are occurring more frequently. A 2016 UN Environment Programme (UNEP) report flagged zoonoses as an issue of global concern. On average, three new infectious diseases emerge in humans every year; and 75 per cent of all emerging infectious diseases in humans are now zoonotic.
What is causing the spike in these diseases? Here’s what decades of scientific research has to say:
Coronaviruses are facilitated by human actions
According to the Intergovernmental Science Policy Platform on Biodiversity and Ecosystem Services, "There is a single species that is responsible for the COVID-19 pandemic – us.”
Not all coronaviruses result in a new zoonotic disease. Without animal-to-human transmission, the current SARS-CoV-2 virus would not have presented itself in the form of COVID-19. Indeed, other coronaviruses are circulating in animals and have not yet infected humans.
Coronaviruses are leaping to humans more frequently because we are providing them with more opportunities to do so. In the last 50 years alone, the human population has doubled and the global economy has almost quadrupled. Rapid migration from rural to urban areas and creation of new urban centres has affected demographics, lifestyles and consumer behaviour.
Environmental changes
Our evolving lifestyles have dramatically altered the land around us. We have cleared forests and other natural areas to create spaces for urban areas and settlements, agriculture and industries. In doing so, we have reduced overall space for wildlife and degraded natural buffers between humans and animals.
Climate change is also a driver of zoonoses. Greenhouse gas emissions–primarily the result of burning fossil fuels–cause changes in temperature and humidity, which directly affects the survival of microbes. Rapid changes to habitat due to unusual weather events such as heat, drought, flooding or wildfires are too rapid to allow ecosystems to balance sudden spikes in populations of group species such as mosquitoes, which can be vectors for emerging diseases. Scheduled for release next month, a new rapid assessment by UNEP and ILRI on zoonotics suggests that epidemics will become more frequent as the climate continues to change.
Behavioural changes
Demand for dairy and meat products has led to the expansion of uniform cropland and intense livestock farming in rural areas and near cities. Livestock often serve as a bridge between wildlife and human infections, meaning pathogens may be passed from wild animals to livestock to humans.
Of particular concern are informal markets, where live, wild animals are kept and sold, often in unsanitary and unhygienic conditions. Viruses and other pathogens may be easily spread among animals that are kept close together; or to the humans who handle, transport, sell, purchase or consume them, when sanitary and protective practices are not followed.
Pathogen changes
Pathogens are always changing to survive in different animals, humans and environments. With the increase of intensive farming and overuse of antimicrobial drugs in both animals and people, pathogens are becoming more resistant to the very medications that might have been effective in treating zoonotic disease.
What COVID-19 is teaching us
COVID-19 is a reminder that human health and environmental health is closely linked. There are about 8 million species of life on the Earth, of which humans are just one. These include an estimated 1.7 million unidentified viruses, recognized as the type that may infect people, existing in mammals and water birds. Any one of these could be transferred to humans, if we don’t take preventative measures now.
The most fundamental way to protect ourselves from zoonotic diseases is to prevent destruction of nature. Where ecosystems are healthy and biodiverse, they are resilient, adaptable and help to regulate diseases.
Greater biodiversity and ecosystem integrity can help regulate diseases by supporting a diversity of species, so that it is more difficult for one pathogen to spread rapidly or dominate. Pathogens, that are passed around among reservoirs in animals is more likely to meet an example of effective resilience–where there is greater diversity.
Genetic diversity builds disease resistance among animal populations and decreases the chances of outbreaks of high-impact animal diseases, according to a 2017 IPBES report. Conversely, intensive livestock farming can produce genetic similarities within herds and flocks, reducing resilience and making them more susceptible to pathogens. This, by extension, exposes humans to a higher risk.
What UNEP is doing
As the world deals with the ongoing COVID-19 emergency and starts to recover from the impact of this global pandemic, UNEP is helping nations to build back better and increase resilience to future crises. UNEP supports countries in delivering stronger science-based policies that back a healthier planet and guide greener investments.
Recognizing that they are still our best chance for a better future, UNEP supports countries as they advance the 2030 Agenda for Sustainable Development, its Sustainable Development Goals, the Paris Agreement and other crucial agreements on issues such as biodiversity, oceans, chemicals and waste management.
With its partners, UNEP is also launching the UN Decade on Ecosystem Restoration 2021-2030, a 10-year effort to halt and reverse the degradation of ecosystems worldwide; and working to develop a new and ambitious Post-2020 Global Biodiversity Framework.
On 5 June, World Environment Day will engage governments, businesses, celebrities and citizens to rethink their relationship to nature and call for leaders to make decisions that put nature in the centre. We must act in solidarity and be informed by science.
This story was updated on 27 May 2020.
