Zoonoses represent a critical intersection between human and animal health, underscoring the necessity of a One Health approach that integrates human, animal, and environmental health strategies. The spread of zoonotic diseases is driven by a complex array of factors.

By Pankaj Dhaka, Simranpreet Kaur, Deepali Kalambhe, J.S. Bedi

Today (Saturday 6 July) is world zoonoses day. It is a day to bring public attention to zoonotic diseases that can have significant public health implications as they can lead to outbreaks and pandemics. Notable examples include of zoonotic diseases are COVID-19, the Ebola Virus that spread from wildlife to humans, leading to severe outbreaks in Africa and the H1N1 Influenza, also known as swine flu (this disease spread from pigs to humans, causing a global pandemic in 2009). The COVID-19 pandemic is regarded to have originated from wildlife, underscoring, in public memory, the potential for zoonotic diseases to cause global health crises.

Zoonoses are infectious diseases that can be naturally transmitted between animals and humans. These diseases are significant as they represent a large portion of all infectious diseases, with an estimated 60 per cent of known infectious diseases being zoonotic in origin. Zoonoses can be spread from various sources, including wild animals (Ebola from primates), bats (Nipah virus and coronaviruses); rodents (spreading diseases like hantavirus and plague) vectors like mosquitoes, flies, and ticks; farm animals (anthrax and bovine tuberculosis from cattle); and, pet animals (like rabies from dogs)

Environmental reasons

The spread of zoonotic diseases is influenced by a variety of existing and emerging factors. These factors can be categorized into environmental, agricultural, social, and economic influences. Understanding these factors is essential for implementing effective prevention and control measures. These include a Change in agricultural practices, Environmental changes, Socio-economic factors and Animal and food industry practices.

For instance, raising healthy animals is crucial for preventing the spread of zoonotic pathogens. Implementing good farm biosecurity measures, such as regular veterinary care and proper sanitation, can help achieve this goal. Moreover, encroachment on natural habitats of wildlife due to the increasing demand for agricultural land accelerates contact between wild animals, domestic animals, and humans, increasing the risk of zoonotic spillover.

Similarly deforestation and habitat destruction activities force wild animals into closer contact with human populations, facilitating the transfer of zoonotic diseases. This is coupled with climate change, that can alter the habitats of vectors (like mosquitoes and ticks), extending the range and activity of these disease carriers.

Rapid urbanization and population growth can lead to overcrowded living conditions, which facilitate the spread of zoonotic diseases. The risk of zoonotic diseases due to urbanisation is compounded by globalization and travel – increased international travel and trade can lead to the rapid spread of zoonotic pathogens across borders.

Animal and food industry practices emanate from intensive high-density animal farming that can create environments where zoonotic pathogens can thrive and spread rapidly. Simultaneously, poor food handling practices, including the consumption of raw or undercooked animal products, can lead to foodborne zoonotic diseases.

How do zoonotic pathogens transmit?

Zoonotic pathogens can be transmitted from infected animals to humans through various pathways. These pathogens include viruses, bacteria, parasites, and fungi, each with different characteristics affecting their capacity to spread and their transmission routes. The common transmission routes include:

Direct contact with infected animals: For example, the rabies virus can be transmitted to humans through the bite of an infected dog.

Consumption of contaminated food: Raw milk can be associated with diseases like brucellosis and tuberculosis. Improperly cooked meat is also a source of many foodborne pathogens, such as E. coli, Staphylococcus aureus, Salmonella, and Clostridium perfringens.

Inhalation of airborne particles: Diseases like Q fever can be transmitted by inhaling contaminated dust from animal products.

Vector-borne transmission: Diseases such as Lyme disease are spread by ticks, while malaria is transmitted by mosquitoes.

Contact with contaminated environments: Pathogens like Leptospira can be contracted through exposure to water contaminated with animal urine.

Preventive measures

A combination of strategies need to be employed to mitigate the risk of zoonotic diseases:

Improved biosecurity on farms: Implementing strict biosecurity measures, such as controlled animal movements, regular health checks, and sanitation, can prevent the introduction and spread of zoonotic pathogens.

Sustainable land use practices: Reducing deforestation and managing agricultural expansion can minimize contact between wild animals and humans.

Enhanced surveillance and reporting: Establishing robust surveillance systems for early detection and reporting of zoonotic outbreaks can help in timely interventions.

Public awareness and education: Educating communities, especially those in high-risk occupations, about zoonotic diseases and prevention methods is crucial.

Vaccination programs: Implementing vaccination programs for both humans (e.g., rabies) and animals (e.g., avian influenza) can significantly reduce the risk of disease transmission.

Safe food practices: Ensuring proper handling, cooking, and storage of food products can prevent foodborne zoonotic diseases.

One Health approach

Zoonoses represent a critical intersection between human and animal health, underscoring the necessity of a One Health approach that integrates human, animal, and environmental health strategies. The spread of zoonotic diseases is driven by a complex array of factors, including agricultural practices, environmental changes, socio-economic conditions, and animal and food industry practices. The implications for public health are profound, affecting occupational groups, rural and urban populations, and potentially leading to global pandemics. Addressing the spread of zoonoses requires comprehensive strategies that encompass improved biosecurity measures, sustainable land use practices, enhanced surveillance and reporting systems, public education, and effective vaccination programs. Additionally, safe food practices must be promoted to prevent foodborne zoonotic diseases. By adopting these measures, we can mitigate the risks posed by zoonotic pathogens and protect both human and animal health.

In countries like India, where over 70 per cent of the population is directly or indirectly involved in agricultural activities, awareness and prevention of zoonotic diseases are paramount. Rural populations often depend on livestock for their livelihood, which increases their exposure to zoonotic diseases. Ensuring the health of both animals and humans is essential for sustainable agricultural practices and economic stability.

The authors work with the Centre for One Health at the Guru Angad Dev Veterinary and Animal Sciences University