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Issues Of The Environment: Coronavirus Just One Of Many Illnesses Spread From Animals To Humans

University of Michigan
University of Michigan School of Public Health

The coronavirus pandemic is ongoing and will be for some time to come.  But it is not the only zoonoses we are dealing with globally or locally.  Zoonoses are illnesses spread from animals to humans.  In this week's "Issues of the Environment," WEMU's David Fair discusses these infectious diseases with Dr. Joseph Eisenberg, chair and professor of epidemiology at the University of Michigan's School of Public Health.


  • Zoonoses are infectious diseases — caused by bacteria, viruses, fungi or parasites — that spread from animals to humans.  They can be transmitted through direct physical contact, via air or water, or through an intermediate host like an insect.  Often, these zoonotic pathogens do not affect the animals in which they reside, but they can represent an enormous risk to humans who have no natural immunity to them. (Source: *directly quoted* https://www.livescience.com/dangers-of-zoonoses-pandemics.html)

  • The COVID-19 outbreak highlights the growing problem of environmental overlap between humans and other animal species and how this interaction creates an environment where zoonotic outbreaks are primed to occur.  The direct link between zoonosis and human activities and demographic growth is established.  Land use modification for urbanization, food production, and agricultural change accounts for around 50% of all zoonotic Emerging Infectious Diseases (EIDs) (Keesing et al. 2010). 

  • Joseph Eisenberg: Dr. Eisenberg is the John G. Searle endowed Chair and Professor of Epidemiology in the School of Public Health at the University of Michigan. 

Zoonotic Disease Outbreaks Becoming More Common

The recent eruption of COVID-19 near a "wet market" in Wuhan, China — where vendors brought a variety of live wild animals together for purchase, slaughter and consumption — calls our attention to a phenomenon captured by a word increasingly understood by the general public: zoonosis.

Zoonoses are infectious diseases — caused by bacteria, viruses, fungi or parasites — that spread from animals to humans.  They can be transmitted through direct physical contact, via air or water, or through an intermediate host like an insect.  Often these zoonotic pathogens do not affect the animals in which they reside, but they can represent an enormous risk to humans who have no natural immunity to them.

The COVID-19 pandemic provides a stark reminder that handling or coming into close contact with wildlife — along with their body parts and/or excretions like blood, spit and urine (the potent mix of which lends wet markets their name) — poses a risk of spillover of the pathogens they host and maintain in nature, and that can lead to zoonotic infections.

Globally, zoonoses are responsible for an estimated 1 billion cases of human illness and millions of human deaths every year. Around 60% of the emerging diseases reported globally are considered to be zoonoses, and 75% of new human pathogens detected in the last 30 years originated in animals.

Zoonotic diseases may be endemic, meaning that they are found in a narrowly defined region or population, or they may be epidemic, when their spread is more far-reaching.  A pandemic is a worldwide epidemic.  COVID-19 has been designated a pandemic by the World Health Organization (WHO).

A wide variety of animal species can carry zoonotic agents, from domestic animals to wild ones. Examples of domestic animal zoonoses include the bacterial diseases E.coli and toxoplasmosis.  Other zoonotic diseases that spill over from wild animal hosts to human populations include West Nile Virus, SARS (severe acute respiratory syndrome), MERS (Middle East respiratory syndrome) and, now, COVID-19.

These "spillover" events are a significant and growing threat to global health, global economies and global security.  Analyses of their trends suggest that their frequency and economic impact are on the rise.

Current investigations of potential zoonotic viruses, funded by the U.S. Agency for International Development's (USAID) PREDICT program, suggest that there are over 1.6 million unknown viruses in birds and mammals. Based on decades of expertise, an estimated 700,000 of these agents could pose a zoonotic risk, according to the Wildlife Conservation Society.

Emergence of these as-yet-unidentified threats results from the ever-shrinking separation between humans and wild ecosystems and organisms.  Changes in human population size and distribution, land use, infrastructure and consumption all impact the wild world, shake out the pathogens lurking in the dark and increase the potential of zoonotic illnesses to emerge.

Faced with the spectrum of zoonotic agents currently at large in the natural world, limiting the chances of contact between humans and wild animals is the most effective way to reduce the risk of emergence of new zoonotic diseases.

This must include closing live animal markets that sell wildlife, strengthening efforts to combat trafficking of wild animals within countries and across borders, and working to change dangerous wildlife consumption behaviors.  Saving wildlife and wild places, while respecting animals and their spaces, can reduce the transmission of zoonoses as the public begins to absorb this new word into their vocabulary. (Source: *directly quoted* https://www.livescience.com/dangers-of-zoonoses-pandemics.html)

Bovine TB Transfer to Humans in Michigan

Between 2002 and 2017, the Michigan Department of Health and Human Services identified three human cases of tuberculosis caused by Mycobacterium bovis that were linked to diseased free-ranging deer, researchers reported in MMWR.  All three cases occurred in hunters, including two who developed pulmonary disease, possibly as a result of aerosol transmission while they field-dressed deer carcasses, the researchers said.  The third patient developed cutaneous TB, likely after injuring his finger while field-dressing a “grossly lesioned” deer. 

According to the report, a four-county region in the northeastern Lower Peninsula of Michigan reports the majority of M. bovis–positive deer in the state.  Since 1995, the state has conducted surveillance for M. bovis among hunter-harvested deer head submissions."  Michigan is the only locale in the United States where ongoing transmission of TB from animals to humans has been documented,” James Sunstrum, MD, clinical associate professor at Wayne State University School of Medicine and director of the Wayne County Health Department TB clinic, told Infectious Disease News.  (Source: *directly quoted* https://www.healio.com/infectious-disease/zoonotic-infections/news/online/%7B7795197e-ae76-4af9-a416-2b6d9d86e6cc%7D/m-bovis-tb-detected-in-michigan-deer-hunters)

Mapping Zoonotic Diseases in Michigan

The Michigan Zoonotic and Vector-Borne Disease Mapper is a tool to display information about certain illness transmitted by bugs and animals in Michigan.  You can search the mapper for reported illness in people, and confirmed infections in animals.  The information provided is gathered from several sources, including:

  • Mosquitoes collected and tested for viruses by local agencies
  • Other sick or dead wildlife collected and tested for West Nile virus and Eastern Equine Encephalitis
  • Animals submitted for rabies testing at the MDHHS Bureau of Laboratories
  • Tick numbers and species submitted by the public to the MDHHS Tick Identification and Testing Program
  • Reported human cases of zoonotic and vector-borne disease (West Nile, Lyme disease, and others) (Source: https://www.michigan.gov/emergingdiseases/)

Human Interaction and Habitat Overlap Fuel Zoonotic Outbreaks

A global political and research infrastructure has grown around the fight against “zoonoses,” or diseases transmitted between vertebrates and humans.  The One Health or Ecohealth approach and its integration of human, animal, and environmental health and the concomitant critique of the epistemological fragmentation of the Western scientific tradition can be applauded, but scientific and political focus needs to shift from zoonotic disease to Human-Induced Disease.  Human-Induced Disease includes both infectious—i.e., zoonoses and disease from animal origin—and non-infectious anthropogenically driven diseases. Human-Induced Disease as the label for diseases—both infectious and non-infectious—caused by human activities and their environmental impact emphasizes the role of the human in disease transmission and could serve reshaping our approach to disease management and prevention.

Zoonotic diseases have been at the cornerstone of the One Health/Ecohealth approach.  Zoonoses incurred an estimated $20 billion in direct costs and over $200 in indirect losses in the last 10 years (World Bank 2010).  These events generate moral panic, legitimate new spheres of legal activity, and spur new arguments for the funding of research.  The arsenal of disease-combatting weapons grows constantly, evidenced by mass immunization or eradication of animal reservoirs.  This dynamic derives from an anthropocentric perception and the psychologically useful imagination of a species barrier.

Most viruses and bacteria are not pathogenic but symbiotic, with humans hosting some 100,000 billion bacteria compared to their own 10 billion cells.  Bacteria have a vital role in human bodily function and are integral elements of human cells (mitochondrion), and viruses constitute at least 10% of human DNA.  Humans share most of the viruses, bacteria, and fungus with the rest of the animal kingdom, and thus it should come as no surprise that zoonotic pathogens were the cause of more than 65% of emergent infectious disease events in the last 60 years, with 75% of these originating in wild fauna (Keusch et al. 2009).  The biologically relevant question is what allows or prevents infection by microorganisms, whether or not the infected species is human.

The direct link between zoonosis and human activities and demographic growth is established.

Land use modification for urbanization, food production, and agricultural change accounts for around 50% of all zoonotic Emerging Infectious Diseases (EIDs) (Keesing et al. 2010).  Demographic, societal, and behavioral change gave rise to Human Immunodeficiency Virus (HIV/AIDS) (de Sousa et al. 2010) and outbreaks of syphilis (D’Angelo-Scott et al. 2015). Anthropogenic environmental change leads to the emergence of infectious diseases in wildlife (Daszak et al. 2001).  The advent of mass travel exacerbates the historically established dissemination of infectious disease along pathways of migration. Examples are bubonic plague (Yersinia pestis), cholera (Vibrio cholerae), seasonal influenza, Severe Acute Respiratory Syndrome (SARS), and malaria (Plasmodium falciparum) (Tatem et al. 2006). The trade in goods and animals is directly linked to outbreaks such as human monkeypox virus in North America (Karesh et al. 2005) or H5N1 in the United Arab Emirates (Naguib et al. 2015).

It is nevertheless common that cause is attributed to the animal and not to human behavior as evidenced, for example, by the mass culling of badgers and the ibex to control tuberculosis or prevent brucellosis in Europe.  This also evidences the diminished value to humans of wild animals and comes despite the Universal Declaration of Animal Rights (UNESCO 1978 and revised, 1989) which states that “action endangering the survival of a wild species, and every decision leading to such act form a genocide, i.e. a crime against the species” (Article 8).  When human health is concerned, even hypothetically, such principles are quickly abandoned in the urge to displace consequence as cause.  Is reducing the risk of transmission by tackling human activities amplifying disease transmission really out of our hands?

Human-Induced Diseases do not only encompass infectious disease such as zoonoses whose spread is enhanced by human activities, but it also includes chronic disease linked to environmental perturbation caused by human activities.  Environmental degradation is a sensitive topic since environmental health is a concept that is still lacking definition, consensus and true global liability and accountability.

The World Health Organization (WHO) estimates that ambient air pollution caused 3.7 million deaths throughout the world in 2012 (WHO and others 2014).  The Organization for Economic Co-operation and Development (OECD) claims this death rate increased by 5% in China, 12% in India (OECD 2014), and 4% worldwide between 2005 and 2010.  It estimated that the annual economic cost of illness and premature mortality linked to air pollution is $3600 billion (OECD 2014)—a figure that is 85% of the world’s annual public budget for human health.  The International Monetary Fund reported the use of fossil energies costs $4900 billion a year (Parry et al. 2014) in disease, premature death, and environmental damage.  This figure is 1.2 times more than the combined public health budgets of 193 countries and yet industries that exploit fossil energies are subsidized directly and indirectly by more than $500 billion annually (iMFdirect—The IMF Blog 2016).

Environmental degradation is estimated to be the cause of 40% of world mortality (Pimentel et al. 2007).  Human activity gives rise to multiple forms of toxic pollution affecting both our health and the environment. For example, production of garments for international markets takes place mainly in developing countries and involves unregulated tannery operations that generate chromium pollutants known to have carcinogenic effects on both animals and humans.  In 2013, industrial plants with poor waste treatment and disposal infrastructure were responsible for the lead pollution linked directly to the death from chronic illness of 853,000 people living mainly in low and middle income countries (Harris and McCartor 2011).  The Institute for Health Metrics and Evaluation also estimated that lead exposure accounted for 9.3% of the global burden of idiopathic intellectual disability, 4% of the global burden of ischemic heart disease, and 6.6% of the global burden of stroke.  UNESCO’s World Water Assessment Programme estimates that industry is responsible for the annual accumulation of 300–500 million tons of sludge, heavy metals, and other toxic wastes, and that 70% of untreated industrial waste in developing countries is dumped directly into water systems (United Nations Educational, Scientific and Cultural Organization 2016).

For people of] poor countries, resource degradation is the most tragic, forced as they are to overuse natural resources from which depends their survival. They are driven to sacrifice their future to ensure precarious everyday life. That is why in many countries, acting against poverty includes protecting the environment.—UN

A plethora of examples is already linking human diseases—both infectious and non-infectious—to environment perturbation in developed and developing countries.  Concerns are also raised regarding the impact of climate change on human disease burden.  Climate change is shifting ecological dynamics leading to potential increase in vector-borne disease such as Lyme disease (Brownstein et al. 2005) or malaria (Martens et al. 1995), zoonotic diseases like hantavirus infection (Tian et al. 2017), and non-infectious disease such as ciguatera fish poisoning (Gingold et al. 2014).

Even though environmental health and human health are deeply connected, environmental health is difficult to protect without consensus on definitions, common objectives between beneficiaries, and long-term planning.  Conventions of international environmental law introduced the concept of legal protection for species, sites, habitats and ecosystems.  Three concepts of nature coexist: It is a Law project (UNESCO 2016) in which the common heritage dimension is underlined; it is a Legal subject (United Nations 2016); or it is a Law purpose (UNEP 2016)?  The International Criminal Court announced in September 2016 that it will now prioritize crimes that result in the “destruction of the environment”, “exploitation of natural resources”, and the “illegal dispossession” of land (International Criminal Court 2016).  Yet legality and illegality are often controversial. Policies intending the liberalization of international trade do not take into account resource consumption, pollution, or negative societal impact in the producing and exporting countries (Pearson 2000).  Traded goods are not priced to incorporate such costs, and as such benefits of trade are distorted.  A multitude of supranational environmental agencies, commissions, programs, and secretariats exist, but there is no global authority able to levy an appropriate pollution tax or fines on national governments or economic agents.

It is becoming increasingly apparent to many that solutions and actions cannot be left to government or supranational government agencies.  Consumers are boycotting products with negative social, environmental, and health impacts such as slavery in clothing factories, harvesting of exotic timber, or methylmercury contamination in seafood.

Environmental citizenship is a recent and theoretically complex concept (Bell 2005).  It is defined by the United Nations Environmental Programme as an “attempt to make environmental conservation and sustainability an important duty of citizenship that citizens all over the world should be aware of” (UNEP).  Many multinational enterprises are now engaged in corporate citizenship programs to promote sustainable development, including the simultaneous consideration of economic growth, environmental protection, and social equity in business planning and decision-making.  Yet the willingness and ability of governments to reflect environmental values of their citizens vary greatly among countries (Pearson 2000).

The individual remains the fundamental element of society.  How powerful can one individual be?  The internet and its powerful networking effect is beyond control of established institutions.  It creates opportunities for horizontal communication, develops new forms of democracy and social participation, and could bring people closer to having impact on issues of common concern such as health, social justice, and the environment (Barcena 1997).  Could billions of individuals, scattered through the world but connected via the internet, become the strongest and most active pillar of environmental protection and thus enhance health and improve social justice?

The term Human-Induced Diseases might have the potential to put the human back into perspective and unify concerns and efforts.  Human-Induced Disease as the label for diseases (infectious and non-infectious) caused by human activities emphasizes the role of human and could serve bringing together scientists, politicians, industrials and laymen in common pursuit.  Human-Induced Diseases need to be named in order to be collectively claimed. (Source: *directly quoted* https://link.springer.com/article/10.1007/s10393-017-1299-9)

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— David Fair is the WEMU News Director and host of Morning Edition on WEMU.  You can contact David at734.487.3363, on twitter @DavidFairWEMU, or email him at dfair@emich.edu

Contact David: dfair@emich.edu
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