Introductory Chapter: The Multiple Challenges for the Effective Control of Zoonotic Diseases

1. Introduction

Zoonotic diseases, those that transmit from animals to humans, have been a longstanding threat to public health, manifesting in outbreaks, epidemics, and even pandemics, as recently occurred with the SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) infection and COVID-19 (Coronavirus disease 2019). Due to their complex nature and myriad challenges, controlling these bacterial, fungal, parasitic, prion, and viral diseases requires a multifaceted approach. From ecological factors to socio-economic dynamics, several interrelated elements contribute to the difficulty in effectively managing zoonotic diseases, requiring multidisciplinary and multisectoral approaches [1, 2, 3, 4, 5, 6].

Poverty significantly contributes to the emergence and spread of zoonotic diseases, transmitted between animals and humans. Impoverished communities often live closely with animals, lack access to clean water and healthcare, and engage in risky behaviours like bushmeat hunting. The consequences, such as income loss and limited healthcare, disproportionately affect the poor. To mitigate this, improving living standards and healthcare access and promoting sustainable practices are essential for reducing the prevalence and impact of zoonotic diseases. Understanding and addressing the poverty-zoonoses connection is crucial for safeguarding human and animal health [7, 8, 9, 10].

Also, understanding and lessening the impact of zoonotic diseases hinges on environmental factors like habitat destruction, climate change, and biodiversity loss, which are highly relevant in addition to socio-economic factors. Environmental factors greatly influence disease emergence and transmission. For example, deforestation disrupts ecosystems, increasing human-wildlife contact and pathogen spread. Climate change alters disease vector behaviour and range, heightening transmission. Biodiversity loss weakens disease regulation, allowing pathogens to proliferate. Addressing these concerns through conservation, sustainable land management, and climate adaptation is vital for preventing future pandemics and safeguarding public health. Prioritising environmental health fosters a resilient ecosystem-human interface, shielding people and wildlife from infectious disease threats [6, 8, 11, 12].

One of the best examples of recent threats is zoonotic influenza, especially H5N1 [13, 14, 15, 16]. Zoonotic H5N1 Influenza, originating in birds, poses a significant public health concern due to its potential to mutate and transmit to humans, causing severe illness and even death. Its ability to cross species barriers heightens the risk of a global pandemic, necessitating vigilance in surveillance, early detection, and rapid response measures. Understanding and monitoring zoonotic H5N1 are crucial to prevent outbreaks, safeguard human health, and mitigate the socio-economic impacts of such a pandemic [17]. Multiple events related to H5N1 Influenza in animals occur in different countries (Figure 1).

Figure 1.

WAHIS: World animal health information system—Latest animal disease events, April 2024. (https://wahis.woah.org/#/home).

2. Bacterial zoonoses

Bacterial zoonotic diseases are crucial in public health, agriculture, and ecosystem management (e.g., brucellosis). These diseases, transmitted between animals and humans, pose significant challenges due to their potential for rapid spread and diverse impacts. Understanding and addressing them are essential for several reasons. Bacterial zoonotic diseases can have severe health implications (e.g., leptospirosis). They account for a considerable burden of illness globally, causing symptoms ranging from mild discomfort to life-threatening conditions. Diseases like anthrax, brucellosis, and salmonellosis highlight the diverse range of bacterial pathogens capable of crossing species barriers [3, 18, 19].

These diseases have economic repercussions. Outbreaks can lead to significant losses in agriculture and livestock industries through decreased productivity, trade restrictions, and the costs associated with disease control measures (e.g., bovine tuberculosis). Moreover, human illnesses result in substantial healthcare expenditures and productivity losses [20, 21].

Furthermore, bacterial zoonoses often have complex transmission dynamics influenced by environmental changes, human behaviour, and animal reservoirs. Addressing them requires interdisciplinary approaches integrating veterinary, medical, environmental, and social sciences. Additionally, the interconnected nature of ecosystems and globalisation facilitates the spread of bacterial zoonotic diseases across geographical boundaries. Therefore, effective surveillance, early detection, and rapid response are essential to prevent outbreaks and mitigate their impacts. Then, addressing bacterial zoonotic diseases is critical for safeguarding public health, ensuring food security, and promoting sustainable development in an increasingly interconnected world [3, 22, 23, 24].

3. Parasitic zoonoses

Parasitic zoonotic diseases play a crucial role in global health due to their complex transmission dynamics and significant impact on both human and animal populations. These diseases, caused by parasites that can be transmitted between animals and humans, pose serious public health challenges worldwide. The importance of parasitic zoonotic diseases lies in several key aspects. They can lead to substantial morbidity and mortality in humans. Malaria, caused by the Plasmodium parasite, and toxoplasmosis, caused by Toxoplasma gondii, are prime examples. Malaria is globally distributed, and many aetiological species are now well-known zoonotic [11, 25, 26, 27].

Parasitic zoonoses often have economic implications, affecting livestock production, agricultural output, and trade. For example, trichinellosis, caused by the roundwormTrichinella spiralis, is a complex disease when humans consume raw or undercooked meat, particularly pork, containing the parasite’s larvae. Livestock, such as pigs, can serve as reservoir hosts for Trichinella. Trichinellosis can lead to gastrointestinal symptoms initially, followed by more severe manifestations as the larvae migrate and invade various tissues [28, 29]. Even parasites that may not develop into adult forms in humans may cause significant disease, as is the case of toxocariasis, caused by Toxocara canis and Toxocara cati [30, 31].

Moreover, these diseases highlight the interconnectedness of human, animal, and environmental health. Understanding the ecological factors driving their transmission is crucial for effective prevention and control strategies. Additionally, parasitic zoonoses underscore the importance of One Health approaches, emphasising collaboration between human and veterinary medicine, environmental science, and other disciplines to address health challenges at the human-animal-environment interface [32, 33, 34, 35].

4. Viral zoonoses

Viral zoonoses account for a considerable proportion of emerging infectious diseases, such as Ebola, Zika, Mpox, and COVID-19. Their ability to cross species barriers means they can emerge unexpectedly and have devastating consequences. These diseases often highlight the interconnectedness of human, animal, and environmental health, emphasising the importance of a holistic, One Health approach to disease surveillance, prevention, and control [36, 37, 38, 39, 40].

Most viral zoonotic diseases can have profound socio-economic impacts, disrupting healthcare systems, causing loss of life, and imposing significant financial burdens on individuals, communities, and governments, as observed during the Zika epidemics in Latin America during 2015–2016 [41, 42, 43, 44].

Studying these diseases offers insights into viral evolution, transmission dynamics, and host-pathogen interactions, informing prevention, detection, and response strategies. Recognising the importance of viral zoonotic diseases underscores the need for interdisciplinary collaboration, global cooperation, and proactive measures to mitigate their impact on public health and society.

5. Conclusions

The One Health approach is crucial for managing zoonotic diseases, illnesses transmitted between animals and humans. By recognising the interconnectedness of human, animal, and environmental health, One Health fosters collaboration among various disciplines like medicine, veterinary science, ecology, and public health. This holistic strategy enables early detection, rapid response, and effective control of zoonotic diseases from diverse aetiologies [45, 46].

Implementing One Health principles allows for better surveillance and understanding of disease dynamics at the human-animal-environment interface. It facilitates the identification of emerging pathogens, risk factors, and transmission pathways, leading to proactive measures to prevent outbreaks. Additionally, One Health promotes interdisciplinary research, enabling the development of innovative interventions, such as vaccines, antimicrobial stewardship, and ecosystem management strategies [47, 48].

The One Health approach is essential for safeguarding public health, animal welfare, and environmental sustainability. Addressing health challenges comprehensively enhances resilience to zoonotic diseases, mitigates risks of pandemics, and promotes the well-being of both humans and animals [49, 50].