Emerging Infection Diseases/Zoonotic Diseases

By Ruwini Rupasinghe, UC Davis

2022-2023 Student Ambassador Cohort - Center for Planetary Health

June 2, 2023

Zoonoses are diseases and infections that are naturally transmitted between vertebrate animals and humans via direct or indirect contact (e.g., through mechanical or biological vectors or fomites)¹. Zoonoses can be classified as either endemic (e.g., brucellosis, Q fever, leptospirosis, rickettsioses, and plague), epidemic (e.g., anthrax, rabies, Rift Valley fever, and leishmaniasis), or emerging and reemerging (e.g., Human immune deficiency virus, highly pathogenic avian influenza, bovine spongiform encephalopathy, and Ebola)². An estimated 60% of emerging infectious diseases (EIDs) are zoonotic in origin³. The emergence of these diseases is often due to dynamic interactions between human, wildlife, and livestock populations and due to rapidly changing environments.

Over the past century, the ecosystems have drastically changed, primarily due to various human activities, such as land-use change, emission of greenhouse gasses, and changes in human behaviors. Therefore, the interactions among wildlife, domestic animals, and humans have increased, augmenting cross-species pathogen transmission. As a result, EIDs and zoonotic events are increasing over time, affecting global health and safety, agriculture, economy, and environmental integrity. The recent SARS-CoV-2 pandemic is an abrupt awakening to the realities of a pandemic and our shared responsibilities at individual, social, national, and global levels. At present, responses to such events primarily focus on post-emergence outbreak control, quarantine, vaccine, and drug development, which requires tremendous effort, resources, and budget⁴. A more proactive approach will be, identifying and mitigating risk factors for potential events of disease emergence and spread, which is crucial to respond more rapidly to future epidemics and reducing the global burden of EIDs. Therefore, holistic, integrated, and multisectoral approaches such as One Health approaches are needed to manage and mitigate the risks of EIDs.

Key facts:

1. There are over 200 known zoonotic diseases. The causative pathogenic agents are bacteria, fungi, viruses, and parasites5.

2. An estimated 60% of known human infectious diseases and around 75% of EIDs are zoonotic3.

3. Annually, zoonoses are responsible for 2.5 billion cases of human illness and 2.7 million human deaths worldwide6.

Resources:

https://www.unep.org/resources/frontiers-2016-emerging-issues-environmental-concern

https://360info.org/special-report-changing-climate-changing-diseases/

References

1. World Health Organization. Expert committee on Zoonoses. WHO Technical Report Series No 40 (1951).

2. United Nations Environmental Program. UNEP frontiers 2016 report - emerging issues of environmental concern. (2016).

3. Taylor, L. H., Latham, S. M. & Woolhouse, M. E. Risk factors for human disease emergence. Philos. Trans. R. Soc. B Biol. Sci. 356, 983–989 (2001).

4. Pike, J., Bogich, T., Elwood, S., Finnoff, D. C. & Daszak, P. Economic optimization of a global strategy to address the pandemic threat. Proc. Natl. Acad. Sci. U. S. A. 111, 18519–18523 (2014).

5. World Health Organization. Zoonoses. (2020).

6. Gebreyes, W. A. et al. The global One Health paradigm: challenges and opportunities for tackling infectious diseases at the human, animal, and environment interface in low-resource settings. PLoS Negl. Trop. Dis. 8, e3257 (2014).