Zoonoses: The Role of Human Activity in their Increased Emergence
At the moment everyone is all too aware of diseases like Ebola, Zika and MERS, but no one stops to wonder what role people have played in their emergence or what can be done about it.
Zoonoses are infectious diseases transmitted from animals to humans, which can be caused by fungi, parasites, bacteria or viruses.
It is important to remember that diseases may not affect animals and humans in the same way; while animals might not express any symptoms, the same disease can be quite serious for humans, and vice versa.
Today, zoonoses account for approximately one billion cases of illness yearly, and for approximately 75% of new infectious diseases in humans.
These staggering figures lead the United Nations Environment Programme (UNEP) to flag the emergence of zoonotic diseases as an issue of concern in 2016, pointing out that it is a matter closely related with the health of ecosystems.
As COVID-19, the newest among these diseases pushes society out of its comfort zone, it is the perfect time to look at the factors contributing to the increased emergence of zoonotic diseases so that appropriate measures can be taken.
Changes in Land Use
Changes in the environment is one of the three types of changes considered by scientists that allow pathogens to move from animal to human hosts, and one primarily caused by human activity.
It is estimated that human activity has altered almost 75% of the Earth’s surface.
In the last two decades of the twentieth century, it is calculated that agricultural expansion was of one hundred million hectares in the tropics alone, which is equivalent to the total area of France and Germany combined.
In order to meet the increasing demand for land for agriculture or settlements, society has encroached natural ecosystems, thus eliminating the buffer that once existed between the wildlife and humans, which in turn has facilitated the spill-over of pathogens between the two.
In addition, climate change has proved to be a key factor enabling the survival of pathogens and their hosts. Evidence suggests that if the current trends in climate change continue, the frequency of outbreaks of epidemic diseases will continue to increase.
Intensified Agriculture and Husbandry
According to studies, in 2015 changes in the agricultural industry were the second-largest driver of disease emergence.
Agriculture is closely linked to the changes in the pathogen hosts, the second of the three types of changes considered by scientists. As the human population continues its rapid growth, demand for animal products has lead to more intensive farming.
Most pathogens originate in the wild, however, it is livestock that acts as the bridge between wildlife and humans hence increase husbandry increases the likelihood of said pathogens being transferred.
In addition, intensive farming often leads to fairly homogenized genetics among herds or flocks. This lack of diversity within populations is extremely hazardous when thinking about diseases, for it is this diversity that usually enhances resilience to pathogens, therefore these populations are becoming increasingly more vulnerable to zoonotic diseases coming from the wild.
Wildlife Trade
Although in most cases livestock acts as a bridge between wildlife and humans, the existence of illegal or poorly regulated wildlife trade is another factor that cannot be ignored.
United for Wildlife estimates that illegal wildlife trade is among the five most lucrative global crimes, giving an idea of the dimensions of this issue. Not only is it the second-largest threat to the survival of endangered species, in the context of this article it is a clear health hazard as it brings humans into direct contact with wildlife, often neglecting to take the appropriate measures to prevent the transmission of zoonoses.
Antimicrobial Resistance
Like most living organisms, zootonic pathogens are continually evolving and adapting to changes in their environment. Changes in pathogens are the third type of change that facilitates the transmission of pathogens between animals and humans.
In zoonoses, evolution is very quick due to the short life-span of the pathogens, thus leading to a quick build-up of resistance to drugs over their short-lived generations. The most common cause of this is the misuse of drugs by people, namely not completing treatments according to medical prescriptions or incorrect self-treatment of diseases.
Unfortunately, with zoonotic diseases, this issue is magnified as it is also affected by the misuse of medication in veterinary medicine. Medication is commonly used in domesticated animals, particularly in intensive husbandry, as a preventative, however, this has further contributed to the build-up of antimicrobial resistance in pathogens.
What can be done
The first step towards tackling this increased emergence of zoonoses is to acknowledge the role human activity has played, as has been described. As a society, it is imperative that we recognize the close relationship that exists between our health and that of our planet, including our ecosystems, their flora, and fauna.
As the COVID-19 pandemic continues, there is continued concern over the economic effect it will have on our society. However, it is important that we acknowledge the role this very economy has played in getting us here. Going forth, we must demand the development of a sustainable economy has a balance between our wellbeing and that of our planet at its core.
But before anything else, think what you can do as an individual. Follow through with your medical prescriptions accurately. Take good care of your pets. Do not take that picture with that wild feline on your next holiday. There is always something each of us can do.
References
- UN News. 2020. First Person: COVID-19 is not a silver lining for the climate, says UN Environment chief. [ONLINE] Available at: https://news.un.org/en/story/2020/04/1061082. [Accessed 12 April 2020].
- UN Environment Programme. 2020. Coronaviruses: are they here to stay?. [ONLINE] Available at: https://www.unenvironment.org/news-and-stories/story/coronaviruses-are-they-here-stay. [Accessed 12 April 2020].
- UNEP (2016). UNEP Frontiers 2016 Report: Emerging Issues of Environmental Concern. United Nations Environment Programme, Nairobi.
