Zoonotic diseases: A neglected public and planetary health frontier
The scale and spread of these diseases are so high that every year, at the global level, the top 13 zoonotic diseases lead to nearly 2.4 billion cases of human illness, and 2.2 million human deaths
The Covid-19 pandemic has impacted human lives and resulted in socio-economic disruption of unimaginable scales. While several hypotheses, counterhypotheses, and even conspiracy theories about the likely origin of Sars-CoV-2 are currently in circulation, the one indicating its zoonotic origin remains the most plausible one.
Simply put, this hypothesis suggests the possibility that a virus that was already circulating in a wild animal without causing disease, underwent certain random natural genetic changes to gain the ability to infect and damage human cells. Subsequently, when a human being came in contact with a wild animal carrying this “novel” virus, the pathogen made the species jump. It thus started a human to human infection chain, which rapidly engulfed the entire humanity.
Though the actual identity of the species of wild animal(s) involved in this event is still under investigation, the catastrophic outcome of this phenomena is on display across the globe.
The prime reason that makes this hypothesis most plausible is that such interspecies spillovers of diseases from animal to human are not new. Rather, such diseases, broadly termed as zoonotic diseases, impact humankind since the beginning of its association with animals.
They are also the most numerous ones. Out of all the human disease causing pathogens identified so far, over 60% are of animal origin. These include the causative agents for several well-known human and livestock diseases such as Tuberculosis, Brucellosis, Anthrax, Leptospirosis, and Rabies.
The scale and spread of these diseases are so high that every year, at the global level, the top 13 zoonotic diseases lead to nearly 2.4 billion cases of human illness, and 2.2 million human deaths. Other than their enormous impact on human health, their footprints on global and national economies are discernible.
Even more unsettling are the new and emerging Infection Diseases, against which neither we nor our immune system are fully prepared. As high as 75% of the diseases catalogued in this group are of zoonotic origin. They include dreaded human diseases such as HIV/Aids, Ebola, Avian influenza, Swine Flu, Zika, Nipah, Mers, and Sars; many of which have caused havoc in several parts of the world in recent times.
Covid-19 is the newest addition to this list.
While they are so prevalent, our responses towards these diseases have been far from satisfactory. It is unfortunate that a problem of such devastating potential has so far failed to elicit the required support from policymakers and resource allocators. Despite repeated warnings from conservationists, veterinarians and public health professionals about the possibility of zoonotic diseases causing large scale disruptions in human lives and activities, they were never given the warranted consideration, either in our planning or in action. It ultimately took a global pandemic of the current scale, coming with an enormous human cost, to spotlight the long-pending discussion on zoonotic diseases and the drivers behind them.
Though the natural genetic changes that make these pathogens more infectious and lethal are outside our control, several field observations and scientific investigations have established that the increased incidences of zoonotic diseases in recent times are a direct consequence of the ongoing abuse of nature.
Our irresponsible actions such as large scale deforestation and encroachment of pristine natural ecosystems; reckless land-use changes either to enhance agriculture and livestock productions, or to provide land for infrastructure and industrial developments; and unsustainable consumption, coupled with unregulated trade of wildlife and their derivatives, often via a long and unhygienic supply chain, provide the enabling conditions for such disease spillovers. These activities expose humans and their livestock to distant wild animals and the pathogens they carry, by shattering the intricate arrangements of niche-separation established through slow and delicate evolutionary manoeuvring by nature, spread over several centuries. The pathogens exchanged during these interactions often end up causing deadly diseases in their new and previously unexposed human hosts.
From this, it is evident that since such diseases are the outcomes of a complex interaction between the ecosystem, animals, and humans, a selective approach of dealing with only human health cannot succeed. Also, after closely witnessing the ongoing global struggle against the virus, it is clear that humanity cannot afford to deal with individual pathogens on a case-by-case basis, and certainly cannot bear the cost of more such pandemics coming in quick succession.
Hence, if we wish to minimise the risk of future pandemics and mitigate its impact, a long-term and holistic approach for ensuring wholesome planetary health, involves humans, animals (both domesticated and wild), and natural ecosystem’s health needs to be pursued. Such a comprehensive approach, recognized as One-Health, should be the target of all our preparedness and responses against the future pandemics of zoonotic origin.
In short, if we wish to aspire to a safe and disease-free future for us and our coming generations, we have to immediately start repairing our fractured relationship with nature. The time for doing this is fast running out, as the next pandemic might be around the corner.
Saket Badola, an Indian Forest Service officer; heads TRAFFIC in India. TRAFFIC is an international network that deals with wildlife trade issues
The views expressed are personal