Medicine has established ways of understanding and managing illnesses, such as infectious diseases, but we are now realising that the ‘causes’ of disease are much broader and far-ranging than we thought. This has fundamental implications for healthcare, argues Deakin bioethicist Dr Simon Coghlan.
Understanding disease-producing factors that our medical systems tend to neglect can help with the prevention and control of illnesses in people. It can also lead to improvements in our care of animals and the environment. An example might help illustrate this idea.
Imagine you have been struck down with an illness in Spring, having developed the all-too-familiar signs of high fever, sore throat, headache, lethargy and muscle aches. Such an illness has causes that lie within your body. You might, for instance, be incubating an influenza virus, which has evolved over millennia to invade epithelial cells in your throat, lungs, and nose.
Your risk of developing a nasty infection is also influenced by the state of your health, age, previous exposure to strains of flu, immunological functioning and even genetic and epigenetic factors.
Causes that lie nearby but outside your body are also identifiable. Consider some of the mechanisms of exposure to pathogens. The influenza virus could have been transmitted to its victim in aerosol or mucous produced by an infected person sneezing or coughing on public transport or at your workplace. Alternatively, it may have been transmitted on human skin via a handshake, or on objects and materials likely to carry infection, such as clothing or furniture.
A recent journal article even found that air travel can seriously increase risks of infection, especially by means of innocent-seeming airport security trays, which are laden with pathogens. Preventive health tools – cleaning surfaces with disinfectants, for instance, and hand-washing stations – are poorly adapted for settings like these, and there is a lack of knowledge about what actions people can take to reduce their own risk of spreading or catching infections, such as coughing into your sleeve.
Other contributing causes relate to health-related behaviours, access to health care and the quality of that care. For instance, you might have missed getting a vaccine, been vaccinated too late or received a vaccine that does not protect you against a strain of the flu virus that has recently mutated.
Prior to each flu season, tracking of global human influenza movement allows vaccinations to be designed and rolled out to vulnerable individuals in many countries, but the process is imperfect and slow. During the unusually deadly 2017 flu season in Australia, many of the victims, including older adults and young children, had been given vaccinations that did not cover a virulent strain of Influenza A.
The causes mentioned so far can be described as proximate or immediate causes of transmissible human disease. Our medical system and a cooperative public have become increasingly well equipped to identify and respond to such causes both inside our bodies and in some environments, such as toilets and hospitals.
But as sophisticated as they are, modern medical systems have tended to ignore a range of disease causes that lie further upstream. Such causes are less obvious than the ones we have discussed, but they are just as important.
The best way to understand upstream causes of illness is by starting with the fact that most infectious diseases have their origin in non-human animals. Remarkably, 61 per cent of the 1,400+ infectious diseases in humans originated in non-human species, and 75 per cent of new and emerging infectious diseases are zoonotic – that is, they spread from animals to humans.
In 2004, a highly pathogenic form of avian influenza hit the headlines. Bird flu, as it is commonly called, occurs in both mass-farmed poultry and in relatively free-ranging poultry belonging to subsistence farmers in poor countries. It can also be spread further afield by waterfowl and migrating bird species. And, in 2009, an influenza (H1N1) pandemic took off from its source in intensively farmed pigs, killing thousands of people. This virus was similar to the one that caused the 1918 Spanish flu pandemic, which resulted in over 50 million human deaths.
Other recent and dangerous zoonotic diseases have included Ebola virus – spread to humans by traffic in the meat of African great apes and also via bats – and SARS, which moved from cave-dwelling horseshoe bats in Yunnan province to wild animals sold in Chinese markets before infecting humans.
The activities of farmers, hunters and many other people who interact with animals very far from where we live can constitute further upstream causes of human illnesses that sometimes become pandemics. The adaptable behaviour of a variety of pathogens shows just how vulnerable we humans are to the infections that afflict many other species on the planet.
Ecosystem health is also responsible for the emergence of pandemic threats. When we cut down forests to build poultry and pig farms close to bats and to other highly stressed wild animals, for instance, we potentially increase the risk of viruses combining with other viruses to produce more life-threatening strains.
In other words, sick ecosystems can lead to sick people. These upstream causes are far removed from the passage of respiratory infections among people in developed countries but they play a role in local disease experiences.
“Fortunately, we are beginning to appreciate this complexity. A new movement called One Health, which began around the time of the 2004 bird flu outbreak, calls for a paradigm shift in our understanding of human well-being.”
The One Health movement urges us to tackle the manifold upstream causes of poor health. According to a 2010 introductory article about the approach, “When properly implemented,” One Health “will help protect and save untold millions of lives in present and future generations.” This perspective has been embraced by major organizations such as the World Organization for Animal Health (OIE), the Food and Agriculture Organization (FAO) and the World Health Organization (WHO).
One Health aims to address environmental, non-human animal and social drivers of human disease by forging partnerships between human and veterinary medicine, and ecology. These disciplines have been relatively isolated from one another in recent times but it was not always so. In attending to the interdependence of human, animal and environmental well-being, One Health – and its sister concept Planetary Health – marks a kind of return to earlier, even ancient, understandings of human health.
The nineteenth century physician Rudolph Virchow, who coined the term zoonosis, for instance, is known for saying “between animal and human medicine there are no dividing lines—nor should there be.” And long before Virchow, Hippocrates alerted us to the dependence of humanity on the natural world in his 2000-year-old treatise On Airs, Waters, and Places. Well before even Hippocrates, indigenous cultures frequently and powerfully pointed to the intimate connections between humans and non-human creatures, and places.
Older cultures, such as those of Indigenous Australians, often expressed the attitude that we ought to care for and manage the health of the natural world. Today, One Health and Planetary Health are again recognising that not just physical health, but also mental health, can be affected by our relations and connections with animals and with green spaces.
One Health’s key insight that the well-being of living things – and of the earth itself – are closely connected gives us a different perspective on wellness and disease, including on the prosaic, albeit often deadly, seasonal flu. Significant influences on human well-being often have their origins further afield and can be affected by how well we understand the health of animals and the environment. A fundamental implication of this new understanding, then, is that we should attend more to the well-being of the non-human world.
Dr Simon Coghlan is a Lecturer in Health Ethics, Professionalism, and Law at Deakin University’s School of Medicine.
Main Photograph: In 2004, a highly pathogenic form of avian influenza hit the headlines. Bird flu, as it is commonly called, occurs in both mass-farmed poultry and in relatively free-ranging poultry belonging to subsistence farmers in poor countries.
Published by Deakin Research on 2 October 2018