Abstract
More than 60% of human infectious diseases are caused by pathogens shared with wild or domestic animals. Zoonotic disease organisms include those that are endemic in human populations or enzootic in animal populations with frequent cross-species transmission to people. Some of these diseases have only emerged recently. Together, these organisms are responsible for a substantial burden of disease, with endemic and enzootic zoonoses causing about a billion cases of illness in people and millions of deaths every year. Emerging zoonoses are a growing threat to global health and have caused hundreds of billions of US dollars of economic damage in the past 20 years. We aimed to review how zoonotic diseases result from natural pathogen ecology, and how other circumstances, such as animal production, extraction of natural resources, and antimicrobial application change the dynamics of disease exposure to human beings. In view of present anthropogenic trends, a more effective approach to zoonotic disease prevention and control will require a broad view of medicine that emphasises evidence-based decision making and integrates ecological and evolutionary principles of animal, human, and environmental factors. This broad view is essential for the successful development of policies and practices that reduce probability of future zoonotic emergence, targeted surveillance and strategic prevention, and engagement of partners outside the medical community to help improve health outcomes and reduce disease threats.
Generated Summary
This review article, published in The Lancet, examines the ecology of zoonoses, which are infectious diseases transmitted from animals to humans. The study explores the natural and unnatural histories of these diseases, emphasizing the impact of human activities on their emergence and spread. The research adopts a broad perspective that integrates ecological and evolutionary principles with evidence-based decision-making to understand and prevent zoonotic diseases. The study also underscores the importance of interdisciplinary collaboration, including public health scientists, ecologists, and veterinarians, in addressing the challenges posed by zoonoses. The scope encompasses the global impact of zoonotic diseases, the role of anthropogenic factors in their emergence, and potential strategies for prevention and control.
Key Findings & Statistics
- More than 60% of human infectious diseases are caused by pathogens shared with wild or domestic animals.
- Endemic and enzootic zoonoses cause about a billion cases of illness in people and millions of deaths every year.
- Emerging zoonoses are a rising threat to global health, having caused hundreds of billions of US dollars of economic damage in the past 20 years.
- The greatest burden on human health and livelihoods, amounting to about 1 billion cases of illness and millions of deaths every year, is caused by endemic zoonoses that are persistent regional health problems around the world.
- Zoonoses made up most of the emerging infectious diseases identified in people in the past 70 years which, although relatively rare compared with endemic zoonoses, are a substantial threat to global health and have caused economic damage exceeding hundreds of billions of US dollars in the past 20 years.
- Apart from the appearance of a pathogen for the first time in human beings, the distinction between endemic and emerging zoonoses can be viewed as temporal or geographical.
- The ability of a pathogen to transmit or spread in a population is commonly quantified by the basic reproduction number, or R, (panel 1).
- Emergence of a zoonosis depends on several factors that often act simultaneously to change pathogen dynamics.
- With more than a billion international travellers every year, infected individuals could potentially spread zoonotic diseases anywhere in the world.
- Apart from the appearance of a pathogen for the first time in human beings, the distinction between endemic and emerging zoonoses can be viewed as temporal or geographical.
- Economic impacts equivalent to US$4.1 billion annually for treatment and control in humans and animals for Echinococcosis.
- More than 579 cases of H5N1 influenza in people have been reported globally, resulting in 341 deaths, and more than 230 million birds have been killed by the disease or culled in counter-epizootic measures.
- For central African countries alone, estimates of annual wild meat consumption total 1 billion kg.
Other Important Findings
- Ecological and evolutionary perspectives can provide valuable insights into pathogen ecology and can inform zoonotic disease-control programmes.
- Anthropogenic practices, such as changes in land use and extractive industry actions, animal production systems, and widespread antimicrobial applications affect zoonotic disease transmission.
- Ecological, evolutionary, social, economic, and epidemiological mechanisms affecting zoonoses’ persistence and emergence are not well understood; such information could inform evidence-based policies, practices, and targeted zoonotic disease surveillance, and prevention and control efforts.
- Multisectoral collaboration, including clinicians, public health scientists, ecologists and disease ecologists, veterinarians, economists, and others is necessary for effective management of the causes and prevention of zoonotic diseases.
- The underlying causes that create or provide access to these new niches seem to be mediated by human action in most cases, and include changes in land use, extraction of natural resources, animal production systems, modern transportation, antimicrobial drug use, and global trade.
- Changes in abundance of animal hosts can strikingly affect disease incidence in people.
- Emergence of a zoonosis depends on several factors that often act simultaneously to change pathogen dynamics.
- Changes to food production systems provide more food security for growing populations, but also change zoonotic disease risks in ways that challenge disease control.
- The effect of endemic zoonotic diseases results in an annually recurring burden to the health and livelihoods of people worldwide, but disproportionately burdens low-income and middle-income countries.
- The techniques with which animals are slaughtered and processed, and how products are stored, packed, transported, and prepared at the place they are consumed, also enable foodborne disease outbreaks.
Limitations Noted in the Document
- The study acknowledges that studies of common endemic zoonoses are often underfunded, whereas studies of zoonotic disease emergence are challenging because they are often intensive, retrospective, and sometimes expensive.
- Emerging zoonotic disease studies are often considered animal-focused or academic research when they are actually translational research efforts essential to guide clinical or public health interventions.
- Standardised data collection and long-term monitoring are needed, as are risk assessments for development of multidrug resistance or multibacterial infections in human beings resulting from antimicrobial use in food animals and from wildlife.
- The text notes that the extent of transfer of antimicrobial-resistant organisms from animals to people is unclear.
- Reduction of the use of antimicrobial drugs in animals might not be a complete solution, because diversity in antimicrobial resistance in people is unlikely to be always related to geographical overlap with livestock.
Conclusion
The study emphasizes that a comprehensive approach to addressing zoonotic diseases requires a broad understanding of their ecological and evolutionary dynamics, coupled with evidence-based decision-making. It underscores the critical role of human activities, such as land-use changes, animal production practices, and antimicrobial use, in driving the emergence and spread of zoonotic pathogens. The authors advocate for multisectoral collaboration, involving experts from various fields, to develop effective strategies for disease prevention and control. The study highlights the need for improved surveillance systems, early detection mechanisms, and the implementation of international health regulations. The review concludes that while the challenges posed by zoonoses are complex and multifaceted, a concerted effort, integrating ecological principles and human health interventions, is crucial for reducing the burden of these diseases and preventing future outbreaks. The authors stress that the global connectivity and human activities are driving forces for zoonoses, necessitating increased awareness and preparedness among health professionals worldwide. A One Health approach is emphasized as a valuable framework for achieving this goal, acknowledging the interconnectedness of human, animal, and environmental health. The study strongly suggests that, in addition to public health measures, the control of zoonotic diseases will require the incorporation of ecological knowledge in public health policies and practices.