Zoonoses, Pandemic Preparedness and One HealthBy Rodrigo Brugada | Tue, 07/06/2021 - 16:49
Humanity is at constant risk of discovering new diseases the hard way. Pandemics come in many forms, not all of them being infectious diseases (as is the case of overweight and obesity). However, the most disastrous ones often are and many of them, at least to some degree, integrate diverse human-animal interactions.
There is a particular category in medical jargon regarding pathologies caused by microbes native to animals that can also cause disease in humans: zoonotic diseases. Most, if not all, of the major plagues and pandemics that have ailed humanity find their origins in animals. Famous examples include the bubonic plague, coming from fleas that affected rats, or the 2009 swine flu. The current pandemic, too, probably came from animal reservoirs.
The exact mechanism in which a specific pathogen may come to infect humans may vary, but there are five major mechanisms at play, according to the CDC:
· First, there is direct contact, in which a person is in close contact with an animal that carries the pathogen or its bodily fluids. This is particularly common in agriculture, where people may come into contact with live animals, animal parts or bodily fluids. Examples of this include avian flu and rabies.
· The second mechanism is through indirect contact, where someone comes in contact with areas, objects or surfaces where animals live and roam, which may have been contaminated. This kind of mechanism usually occurs at farms or with pets at home. Examples of this would be toxoplasmosis, carried by cats, or salmonella, carried by turtles.
· The third mechanism involves diseases carried by vectors, usually insects. Some examples of this would be malaria, carried by mosquitos, or Lyme’s disease, carried by ticks.
· The fourth and fifth ones involve the contamination of food and water, respectively. In the case of foodborne illnesses, the usual culprit is spoiled food. But in the case of zoonoses, this usually refers to food that may not be spoiled but still has microbes. These may come from the food itself, as is the case with unpasteurized milk or raw eggs, or contamination with bodily fluids from another animal. In the case of waterborne illnesses, the usual culprit is commonly the latter.
Zoonotic diseases abound as both severe threats and minor nuisances. The diseases that represent threats to public health are collectively known as emerging diseases. In the specific case of SARS-CoV-2, while there is no well-established cause yet, evidence presented on a paper published by Frontiers in Public Health points to a probable animal origin.
The discussion is further enriched by approaching it through the social dynamics at play that may affect how diseases emerge and spread. Agricultural and farming practices play a crucial role in a transmission mechanism, due to several worrisome practices. Industrialized food supply represents substantial damage to the overall balance of microbes in the environment and represents a critical step in transmitting zoonotic diseases, according to PETA.
Industrialized animal farming practices often demand animals to be kept in close proximity to one another. This creates a problem as infectious diseases in animals can spread easily and swiftly. One of the most commonly cited examples of how this poses a threat is the influenza virus in pigs and poultry farming, as evidenced by an article on Nature. Having different species of animals hosting the influenza virus in crowded spaces creates more opportunities for the virus to mutate. These mutations may be inconsequential but in some instances they might mean that a single strain of the virus can infect both poultry and pigs. Add humans to the equation and you get the potential for pandemic-proportion viruses.
The other critical component of industrialized farming is the widespread use of antimicrobial agents. While this may protect animals from certain infections, mostly bacterial ones, the industry fails to consider that bacteria evolve. Having antibiotics in their environment will make bacteria that can resist them thrive, explains the OECD. This leads to an increase in the use of antimicrobials, creating a vicious cycle that is already signaled as a problem even among humans. Bacteria present in animals also coexist with bacteria in other environments, like rivers where wastewater is dumped. Here, the resistant bacteria can “teach” the other bacteria how to resist antimicrobials, eventually entering human environments where they start spreading. As Tiago Arantes, General Director of MSD Animal Health in Mexico states: “prevention is just as important for animals as it is for humans. We need to be constantly proactive and work to avoid future crises. Animal and human health are closely related.”
Other social and economic activities can also foster the sudden appearance of an emerging disease. This is particularly clear in those economic activities that shorten the distance between humans and other animals, be it directly or indirectly. One such example is the case of the timber industry. First, the work itself demands direct contact through delving into forests where wild animals dwell. Meanwhile, deforestation puts pressure on species that live in those environments and forces them to migrate, thus making contact easier.
Besides the social dynamics that provide more opportunities for the emergence of these diseases, some provide more accessible options for them to spread. One of the clearest examples is how plagues tend to appear in crowded areas such as cities and how they follow the same routes humans used for moving goods and people. This fact becomes highly relevant in the globalized, interconnected world we live in, wherein diseases can spread faster.
Given the complexities entrenched in these social and economic dynamics and their permanence in our current societies, something must be done to curb the emergence of new pandemics. One model that tries to provide a framework for this to happen is One Health. The One Health Commission defines it as “a collaborative, multisectoral and trans-disciplinary approach – working at local, regional, national and global levels – to achieve optimal health and well-being outcomes recognizing the interconnections between people, animals, plants and their shared environment.” This initiative represents an effort to not only focus on the human part of health. While it remains a model with a particular interest in human health, it broadens the horizons of what health itself entails and provides analytic frameworks that help put human activities, and their consequences, in perspective.
This framework provides more and better opportunities for preventing a pandemic or swiftly responding should one emerge. One Health proposes several steps to reach this aim, like deepening our understanding of the causes of disease emergence, the ecology of the agents involved and their animal hosts. Other key actions include creating a collaborative, intersectoral and cohesive network to ensure broader and earlier action at different levels, including the policy level.
Three major international organizations – WHO, FAO and OIE – have jointly published a guide that provides principles and best practices to assist countries in achieving sustainable and functional collaboration at the human-animal-environment level. The organizations present key actions to ensure the development of national and international networks to prevent disease and ensure local and global preparedness. An essential aspect for this approach is that actions must be taken worldwide and involve all relevant stakeholders, including transnational corporations. As Inger Andersen, Undersecretary General of the UN and Executive Director of the UN Environment Program, stated during a press conference on the launch of the One Health High-Level Expert Panel: “To end the three planetary crises of climate change, biodiversity loss and pollution that threaten our peace and prosperity, we have to understand that human, animal and planetary health are one and the same. As Dr. Tedros pointed out, human health does not exist in a vacuum. Illnesses that jump from animal to human as a result of degraded natural environments and unsustainable use of animal resources drive this message home – COVID-19 is the most devastating example of this.”
There are still opportunities regarding environmental health that must be addressed, according to Andersen. “This means ending the over-exploitation of wildlife and natural resources. This means changing global dietary patterns. This means farming that is nature positive. This means finance flows that do not destroy nature. And this means investing in science, partnerships across disciplines and capacities so that we are able to prepare and prevent the next pandemic.”