Epidemiological Surveillance to Better Anticipate Zoonoses

The emergence of infectious diseases in humans originates primarily in the animal kingdom. Accelerated by the exploitation of the Earth and its resources, these zoonotic diseases—though well-known and monitored—are growing in scale. Global authorities are urging increased vigilance to anticipate new outbreaks before they gain momentum.

 

The Threat of Zoonoses

Each year, some 2.5 billion people, primarily in low- and middle-income countries, fall ill from a disease of animal origin—known as a zoonotic disease—and 2.7 million die from it. These diseases, which are shared between animals and humans, pose one of the greatest threats to public health and the global economy. The same outbreaks can cause serious illness in both humans and animals, resulting in productivity losses for livestock operations and farms. In the last two decades alone, zoonotic diseases have caused economic losses of more than $100 billion. And that does not include the cost of the COVID-19 pandemic, which is projected to reach $9 trillion over the next few years. And yet our solutions to combat the emergence of these diseases in humans remain fragile. Global bodies are rallying around the OneHealth concept to try to slow the emergence of new diseases. Human health is intrinsically linked to the health of the environment, biodiversity, and animal health. In fact, 60% of emerging diseases are of animal origin. Over the past three decades, approximately 30 new human pathogens have been identified, and 75% of them are of animal origin. Animals are therefore an undeniable source of new human pathogens, particularly viruses. Although viruses represent only a fraction of the approximately 1,400 known human pathogens, their impact on global human health is disproportionately greater. Coronaviruses—which are the subject of so much discussion—transmitted from bats to camels (MERS), civets (SARS-CoV-1), or pangolins (to be confirmed for SARS-CoV-2) and then to humans are just the tip of the iceberg. We must not forget HIV, which originated in non-human primates; Ebola, which originated in bats; or the H5N1 and H1N1 influenza strains, which originated in birds and pigs, respectively. The list goes on. Approximately 89% of the 180 recognized RNA viruses capable of harming humans are zoonotic. And with the increased use and exploitation of wildlife, the rise of intensive and unsustainable agriculture, and the well-known climate crisis, this trend is far from reversing. The recent COVID-19 pandemic reminds us of this all too well.  

Biodiversity, Livestock, Wildlife, and Epidemics – OneHealth

             - Livestock: An Epidemiological Bridge

  Globally, an increase in the emergence of infectious diseases and epidemics appears to be correlated with an accelerated loss of biodiversity and a significant rise in animal production—and the two are by no means unrelated. By cross-referencing several open-access databases on human and animal health, livestock growth, and biodiversity loss, an analysis shows that the number of epidemics recorded in humans in each country increases in correlation with local biodiversity loss. The emergence of epidemics would thus be a worrying indicator for species conservation—which is not on the right track. And while the relationship between the number of endangered species and the number of epidemics increases until it peaks and then declines, the risk of epidemics, on the other hand, does not decrease with the disappearance of species. On the contrary, it is exacerbated by the increase in livestock populations. Indeed, the global increase in livestock directly impacts wildlife and the number of epidemics among humans and domestic animals. It acts as an epidemiological bridge, facilitating the transmission of infectious agents from the animal world to humans. The challenge is therefore twofold. But while livestock are in close contact with human populations and can serve as a primary vector for disease, it is wildlife that is the source of the majority of zoonoses. Approximately 70% of emerging diseases originate specifically from wild animals .  

            - Wildlife as a source of a greater diversity of pathogenic organisms

The risks of disease emergence associated with the trade in wild species remain the greatest unaddressed challenge facing current epidemiological surveillance efforts. The uncontrolled exploitation of wildlife—whether for personal use or for profit, legal or otherwise—brings humans into direct contact with a myriad of unknown species. And wild animals that are imported, hunted, or raised and then transported to wildlife markets are often kept in conditions that promote the transmission of disease. Overcrowding, filth, and a lack of adherence to hygiene and safety regulations contribute to stress and immunosuppression in animals, as well as the spread of disease. Poor compliance with hygiene and safety standards, combined with close contact between non-endemic wild species and humans, is enough to create a zoonotic hotspot. And although the Convention on International Trade in Endangered Species (CITES) regulates the international trade in wild species, many markets around the world meet these criteria even though disease surveillance is largely absent there. Only a few countries enforce strict veterinary import controls. And, to date, there are still no global regulations governing the screening for pathogens associated with the international trade in wild species. Yet epidemiological surveillance of pathogens and their interaction with wildlife are central to risk management and the response to emerging pathogens.  

Epidemiological Surveillance Needs to Be Strengthened

            - Several Decades of Surveillance

  The threat of emerging zoonotic diseases is not new. For several years now, researchers have been working to identify the pathogens with the highest zoonotic risk and predict outbreaks in humans in order to better control them. In 2009, the United States Agency for International Development (USAID) launched the PREDICT project with the aim of detecting and identifying zoonotic viruses with pandemic potential. Over the course of 10 years, 164,000 animals and humans were screened, and 949 new viruses were detected in zoonotic hotspots across 30 countries. And over the next 10 years, researchers hope to sequence all these viral strains to expand our understanding of pathogenic agents at the human-animal interface. However, epidemiological surveillance efforts are not yet fully developed. Due to a lack of resources and funding—and despite the global significance of the consequences—these efforts are often pushed to the sidelines.  

            - Incomplete and unevenly distributed surveillance

According to the World Organisation for Animal Health (WOAH), only 125 reference laboratories are certified to detect the pathogens in question, and their distribution does not reflect the risks of emergence. Furthermore, they are not distributed based on risk but rather on political considerations. As a result, Southeast Asia, Africa, and Central and South America—which are actually at higher risk of experiencing a zoonotic outbreak—are home to only 38% of the reference laboratories. Although the quantitative figures do not take into account the resources or the scale of these infrastructures, it is clear that certain zoonotic hotspots lack facilities capable of conducting effective surveillance. Conversely, some countries are turning to centralized biosurveillance, which is often costly and subject to the political whims of the countries in charge. As such, these solutions are not scalable. According to experts, and given the global stakes involved with emerging diseases, a decentralized surveillance system is preferable. This would allow local wildlife and public health professionals to detect diseases year-round, at the source. Such screening was not technologically feasible after the emergence of the H1N1 influenza virus in 2009. But modern and now affordable technologies enable rapid on-site processing of biological samples, whole-genome sequencing, and metagenomic analysis of pathogens. Widespread, systematic, and above all proactive screening for pathogens can be implemented on a large scale, in both remote and central areas.  

            - Prioritize preventive surveillance

Particular emphasis must be placed on the preventive aspect of these screenings, in both animals and humans. Indeed, all too often, such screening begins in response to an epidemiological outbreak among humans. However, its importance lies primarily in the local, proactive, and regular monitoring of high-risk pathogenic family groups. It is important to detect the early circulation of zoonotic agents between humans and animals, which are often difficult to identify in the early stages of an epidemiological spillover. To make this surveillance as effective as possible, a global public database on the characteristics and populations of high-risk pathogenic organisms would enable real-time tracking of trends and changes in pathogenic organism populations. Data on strains, hosts, and regions—as well as changes in hosts, mutation rates, or reservoirs—could be recorded to enable rapid, global alerts.  

Anticipate to Mitigate More Effectively

However, even with this knowledge, these measures are sometimes insufficient. It is impossible, for example, to deny the threat posed by coronaviruses. And although this threat was identified early on, it did not prevent the pandemic from spreading. Indeed, after bats were recognized as reservoirs for numerous zoonoses such as Hendra, Nipah, SARS, MERS, and Ebola, surveillance of them was stepped up. Surveillance of a cave in southwestern China between 2011 and 2015 revealed 11 new coronaviruses. Following this discovery, 1,497 people were tested between 2015 and 2017 in the surrounding districts of Yunnan, Guangxi, and Guangdong in China, and 9 (0.6%) tested positive for bat coronavirus antibodies. A warning, highlighting the pandemic potential of bat coronaviruses in this region, was published in September 2019. But apparently, this was not enough to stop the pandemic that followed, despite all the indicators pointing toward a zoonotic event. This demonstrates that a gap still exists between research, surveillance, and the actual implementation of safety measures to anticipate and mitigate a potential outbreak. These shortcomings are what global bodies aim to address, particularly in light of the challenges that appear to be on the horizon. The United Nations Environment Programme (UNEP) and the International Livestock Research Institute (ILRI) recently published a report titled “Preventing the Next Pandemic: Zoonotic Diseases and How to Break the Chain of Transmission.” The report identifies 10 measures that governments can implement to limit future zoonotic outbreaks:

1. Invest in interdisciplinary approaches, including One Health;
2. Expand scientific research on zoonotic diseases;
3. Improve cost-benefit analyses of interventions by including the full cost of the societal impacts of the disease;
4. Raise awareness about zoonoses;
5. Strengthen surveillance and regulatory practices related to zoonotic diseases, including in the agri-food sector;
6. Encourage sustainable land management practices and develop alternatives for food safety and livelihoods that do not rely on the destruction of habitats and biodiversity;
7. Improve biosecurity and pathogenic control, identify the main drivers of emerging diseases in livestock operations, and promote proven measures for the management and control of zoonotic diseases;
8. Support the sustainable management of terrestrial and marine landscapes that promote the sustainable coexistence of agriculture and wildlife;
9. Strengthen the capacity of health stakeholders in all countries; and
10. Operationalize the One Health approach in the organization, implementation, and monitoring of land use and sustainable development, among other areas.

  A new epidemiological perspective that integrates values associated with both wild and domestic animals, as well as the environment in which we live, therefore seems necessary to reduce health risks and protect biodiversity. One thing is certain: if humanity continues to exploit wildlife and flora and destroy our ecosystems, the COVID-19 pandemic will not be the last. We will have to get used to devastating zoonotic events, regardless of our level of surveillance.