The effort to fight emerging infectious diseases must be holistic
As the coronavirus continues to spread, we bear witness to the unprecedented connectivity that defines our global community. Connections are not restricted to people; they also occur among species and across ecosystems. In this way, the emergence of the coronavirus is a powerful reminder of the interdependence of human, animal and environmental health and the need to view health — and disease — through a holistic, rather than human-centered, lens.
Emerging infectious diseases (EIDs), particularly those originating in animals, termed “zoonoses” or “zoonotic diseases,” are one of six growing issues of global concern highlighted in the United Nation Environment Programme’s Frontiers 2016 Report. The report estimated that roughly 60 percent of all human infectious diseases and 75 percent of EIDs are zoonotic. Examples include Zika virus, Lyme disease, hantavirus, West Nile virus and Ebola.
The emergence of novel pathogens is not unusual. One new infectious disease in humans is thought to emerge roughly every four months, though not all are serious or well-described. Rodents, primates and bats seem to be especially important hosts or reservoirs of pathogens.
Disease dynamics cannot be understood, nor addressed, by focusing on human health alone. A well-established body of research shows that the risk of EIDs is strongly correlated with environmental, ecological and socioeconomic factors. These factors, acting independently or in concert, can affect the diversity of pathogens in a region, the prevalence of those pathogens in animal populations, the frequency of contact among people, domestic animals and wildlife reservoirs and the spillover and spread of EIDs through human populations.
Human activities, such as wildlife trade, deforestation, urbanization and land conversion, are key drivers of environmental changes that promote and amplify EIDs. Some links are direct and obvious, such as the wildlife trade that moves hundreds of millions of animals around the world to be used as food, in traditional medicine, as pets, or other purposes. But other links are indirect. Logging and road construction in forested regions increase human exposure to wildlife and the infectious pathogens they may harbor. Such loss of biodiversity can reshape entire ecological communities, lead to higher densities of species that may be potent reservoirs of disease, and increase exposure risk because infection prevalence is no longer diluted among host species that vary in susceptibility.
Degraded environments influence social dynamics among people by causing or exacerbating resource scarcity, poverty and conflict. As a result of these shifting social dynamics, EIDs can worsen because of poor sanitary conditions, malnutrition, illness, human displacement, forced migration and the establishment of high-density settlements like refugee camps.
As we now see, the burden of zoonotic EIDs extends far beyond human health. In the last two decades, the direct costs of emerging diseases have been placed at $100 billion, with indirect costs to economies exceeding $200 billion. Projections show costs could have reached trillions of dollars had outbreaks become pandemics. Such economic consequences reverberate through private and public sectors to impact a wide variety of social and environmental programs and investments, as well as carry opportunity costs that are difficult to ascertain. Prevention and mitigation strategies addressing the drivers of EIDs are more cost-effective in the long term, often generating a 10-fold return on investment. Proactive measures must be enacted globally before problems become intractable or cost-prohibitive.
Fortunately we can draw upon insights from recent interdisciplinary initiatives. Many scientists, scholars and practitioners working in the field of One Health, which promotes a holistic approach to environmental, animal, food and human health, have advocated for a variety of policy and governance interventions. These strategies address trade and illegal harvest of wildlife, land use changes that promote the emergence of EIDs and the need for targeted global surveillance to identify novel pathogens. The Planetary Health Alliance is a consortium of universities, NGOs, research institutes and government entities around the world focused on understanding and addressing the health impacts of global environmental change. These and other groups have found strong evidence that disease regulation is an important ecosystem service that remains under appreciated by the public and decision-makers. This issue is likely to be a discussion point at upcoming international congresses like the Convention on Biological Diversity and the IUCN World Conservation Congress.
Coronavirus is neither the first nor last EID pandemic that the global community will face. Although the toll on people and economies will rightfully summon the most attention and action, let’s not overlook the environmental, ecological and social dimensions that underlie the emergence and spread of infectious disease. By looking through the broad lens of One Health, we can see the many, but still missed, opportunities to prevent and reduce the threat of emerging infectious diseases.
Amanda D. Rodewald is the Garvin professor and senior director of conservation science at the Cornell Lab of Ornithology, faculty in the Department of Natural Resources at Cornell University and faculty fellow at Cornell Atkinson Center for Sustainability. Views expressed in this column are hers alone and do not represent those of these institutions.