July 6, recognised as World Zoonoses Day, commemorates the historic achievement of Louis Pasteur, who administered the first successful rabies vaccine in 1885. While this milestone marks a triumph in medical science, the real significance of zoonotic diseases reaches far beyond. Zoonoses—diseases transmitted between animals and humans—are not isolated events. They are shaped by the way we interact with animals, ecosystems, and each other. This day invites us not only to reflect on past victories but also to examine the deeper drivers, consequences, and inequities associated with the emergence of zoonotic diseases.

What Makes a Disease Zoonotic?

A zoonosis is any infectious disease that can be naturally transmitted between vertebrate animals and humans, caused by a wide range of pathogens: viruses (e.g., SARS-CoV-2, Ebola, CCHF, Avian Influenza), bacteria (e.g., Salmonella enterica, Brucella spp., Bacillus anthracis), parasites (Toxoplasma spp., Trichinella spp.), fungi (Cryptococcus neoformans, Aspergillus spp.), and even prions (Bovine Spongiform Encephalopathy (BSE) also known as mad cow disease). Some zoonoses, like rabies or anthrax, are well-known and deadly. Others, like Hepatitis E, are underestimated but globally widespread. According to the WHO, over 60% of known human pathogens are zoonotic, and 75% of emerging infectious diseases have an animal origin. HIV itself was once zoonotic—before adapting to human-to-human transmission.

Transmission Routes and Everyday Risks

Zoonotic pathogens reach humans through various channels:

• Direct contact with animal secretions, blood, or excreta
• Indirect contact with contaminated surfaces (e.g., barns, soil, cages)
• Vector-borne transmission via mosquitoes, ticks, or fleas
• Foodborne infections via undercooked meat, raw dairy, or unwashed produce
• Waterborne transmission from contaminated water supplies

Even domestic animals can serve as silent reservoirs for zoonotic pathogens. Companion animals such as cats and dogs have been linked to the transmission of Toxoplasma gondii, Giardia lamblia, and Bartonella henselae. On a broader scale, wildlife markets, hunting practices, bushmeat consumption, and the exotic animal trade—especially involving primates, rodents, or bats—create high-risk interfaces for zoonotic spillovers.

Environmental Disruption and the Rise of Spillovers

Spillover—when a pathogen jumps from an animal host to a human—is not a rare anomaly, but a predictable outcome of ecological disruption. Zoonoses are not random accidents; they are symptoms of a planet under pressure. Deforestation, climate change, industrial livestock farming, and the wildlife trade are major contributors. A 2020 UNEP report linked increased zoonotic pandemics to the anthropogenic (human-caused) destruction of ecosystems and the rise in global meat demand. Encroachment into wild habitats and reduced biodiversity create new interfaces for disease transmission, especially in tropical regions where species are forced to coexist unnaturally due to ecological stress.

The problem is escalating: spillover events have tripled since the 1980s, and up to 850,000 unknown viruses in birds and mammals could theoretically infect humans. These risks are no longer hypothetical—they are ecological feedback loops, exposing deep flaws in global food systems, land use policies, and trade patterns.

Beyond Biology: Inequities and Invisible Burdens

Zoonotic diseases disproportionately affect low- and middle-income countries, where veterinary services, diagnostics, and outbreak surveillance are limited. Within societies, smallholder farmers, migrant labourers, and women in caregiving and food roles are more exposed but underprotected. While many zoonoses originate in animal reservoirs, the social determinants of exposure, vulnerability, and care are profoundly unequal.

Veterinarians and frontline public health workers are at high occupational risk, especially in contexts with limited PPE or training. Yet their knowledge and lived experiences are often marginalised in global health policy. Tackling zoonoses means elevating local expertise, community perspectives, and culturally embedded practices—not just imposing biomedical models from above.

Zoonoses and Antimicrobial Resistance (AMR): A Dangerous Intersection

Industrial livestock farming doesn’t just drive zoonoses—it fuels antimicrobial resistance (AMR). The prophylactic use of antibiotics in animals leads to resistant pathogens that enter the human population through food, water, or direct contact. Without strict regulation, improved biosecurity, and universal access to diagnostics, the dual threat of zoonoses and AMR will only intensify. These are not separate crises—they are intersecting syndemics, demanding integrated solutions.

One Health: From Framework to Global Action

The One Health concept acknowledges that human, animal, and environmental health are inseparably linked. But turning this into action requires more than inter-ministerial coordination. It demands:

• Joint surveillance systems across sectors
• Genomic technologies to detect early spillovers
• Cross-border data sharing and transparency
• Community-led education and behaviour change
• Reforms to global trade, agriculture, and wildlife governance

And most importantly, it requires rethinking development itself—shifting from extraction to regeneration, from inequality to inclusion, from crisis response to resilience building.

Final Thought: Zoonoses Are Warnings

On World Zoonoses Day 2025, we must see zoonotic diseases not merely as biological phenomena but as biopolitical signals—indicators of unsustainable systems, eroded habitats, and neglected communities. These diseases are not emerging from nature’s cruelty, but from our failure to coexist with nature responsibly. They reveal how extractive economies, deforestation, industrial farming, and global inequality converge to create environments where pathogens can leap from animals to humans with alarming ease.

Each outbreak is more than a health crisis; it is an ecological message—urgent and unheeded. With every spillover, the Earth warns us. These warnings are not random, nor are they isolated. They are part of a pattern driven by our collective actions and inactions. The question is not only how we can prevent the next pandemic, but whether we are willing to confront and transform the systems that continue to generate them. Without shifting the underlying drivers—be it land use, wildlife exploitation, or global trade—we will remain vulnerable.

The deeper we look into zoonoses, the clearer it becomes: our health depends on the health of all living things. Protecting biodiversity, strengthening equitable health systems, and promoting One Health principles are not optional—they are essential pillars of global survival. On this day, let us recommit not only to science but also to justice, sustainability, and a renewed sense of shared responsibility with the living world.

By ISID Emerging Leader, Dr Gültekin Ünal

Select References

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