Zoonoses: The Role of Wildlife in the Emergence of Human Diseases Is Being Questioned

According to a report by the International Union for Conservation of Nature (IUCN), contact with wild animal species is not the primary source of zoonoses transmission. What concerns the IUCN Species Survival Commission most is the disease risk associated with the poorly regulated or poorly monitored trade in domestic animals and animal products.   The report, titled “Situation Analysis on the Roles and Risks of Wildlife in the Emergence of Human Infectious Diseases ,” is based on an analysis of some 5,000 scientific sources spanning three decades. According to the findings, 99% of human cases of zoonoses are believed to originate from domestic animals or their byproducts, as well as from human-dominated environments. These transmissions occur through direct contact, food , water, or vectors such as insects. The same report highlights the small number of confirmed cases—that is, those based on published evidence (47 cases over the 28 years studied)—which falls far short of the figures typically cited. However, the IUCN stresses that the scarcity of documented evidence should not overshadow “the risk of the spread of new pathogens, as even isolated events can have major consequences .” This analysis of the situation resonates particularly strongly with the COVID-19 pandemic. In this context, it is nevertheless more difficult to establish a link between zoonoses and direct interactions with wildlife, even though the current pandemic has raised authorities’ awareness of health risks associated with wildlife and led to calls for enhanced placement under surveillance of these wild animals. Studies have even developed mathematical models to estimate risks by categories of pathogens, reservoirs, and animals likely to have a sufficiently weak interspecies barrier and thus pose a zoonotic risk. In conclusion, the authors in no way recommend any bans that would hinder global trade; quite the contrary: transparent trade has better traceability than illegal and opaque trade. Therefore, a “One Health” strategy is proposed for global surveillance of the circulation of pathogens or potentially pathogenic agents. “ Although many diseases may have originated in wild animals in the past, the available evidence clearly indicates that interactions with domestic animals are a much more significant source of zoonoses in humans. If we continue to increase our production of animal-based foods, we will not only cause greater biodiversity loss but also increase the risk of future pandemics. We must rethink how we interact with the natural world and preserve the ecosystems that serve as natural ecological barriers to maintain the balance between humans, domestic animals, and wildlife.” To date, there are more than 200 zoonoses. They can be endemic, as in the case of rabies, the Ebola virus, and salmonellosis, or (re)emerging, such as the coronaviruses responsible for severe acute respiratory syndrome (SARS-CoV-2) or Middle East respiratory syndrome (MERS-CoV). Some, after spreading to humans, mutate and become human diseases, such as AIDS (HIV). In total, 60% of human infectious diseases are of zoonotic origin .