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Zoonoses: Preserving biodiversity is the key

The Last Jungle in Cambodia, Orange Dust, near Sihanoukville, Deforestation in Cambodia. Image credit: Igor Sokolov / 123rf Zoonoses concept.
Deforestation scenes from Cambodia. Deforestation and loss of biodiversity is a risk factor for the emergence of zoonoses. Image credit: Igor Sokolov / 123rf

This week marked an importance observance which went overlooked by large swathes of the media, including this publication. World Zoonoses Day took place on July 6th, coinciding with the anniversary of the first rabies vaccine administered by French biologist Dr Louis Pasteur in 1885. 

Zoonoses, as explained by the World Health Organization (WHO), refer to “any disease or infection that is naturally transmissible from vertebrate animals to humans.” However, the World Biodiversity Council estimates there to be 1.7 million undetected viruses in the animal kingdom. Of these, 827,000 could spread to humans.

The COVID-19 pandemic drew attention to zoonoses, with the most common theory being that the disease in itself a zoonosis spread from animals to humans in a wet market in Huanan – considered to be the crisis’s “Ground Zero”. It is worth noting, however, according to one study published in May that “more investigation is still needed to determine the origin of the pandemic. Theories of accidental release from a lab and zoonotic spillover both remain viable. Knowing how COVID-19 emerged is critical for informing global strategies to mitigate the risk of future outbreaks”. Nonetheless, even as we investigate the origins of this crisis, it is important to note that zoonoses are a public health risk and deserve our attention. 

In India, the problem is mounting. As a study published last year outlined, “zoonotic diseases have been increasing globally as well as in India. Of 1407 human pathogens, 816 were zoonotic…These include 538 bacteria and rickettsia, 317 fungi, 208 viruses, 287 helminths, and 57 protozoa. The study also highlighted that as many as 177 (thirteen percent) of the total pathogens were emerging or reemerging, and of these 130 (75 percent) were classified as zoonoses.” 

In India, the study states, “the major public health zoonotic diseases are rabies, brucellosis, toxoplasmosis, cysticercosis, echinococcosis, Japanese Encephalitis (JE), plague, leptospirosis, Scrub typhus, Nipah, trypanosomiasis, Kyasanur forest disease (KFD), and Crimean-Congo hemorrhagic fever. The CBHI provisionally reported around 110 cases of rabies, 1674 cases of JE, 14971 cases of H1N1, 57813 cases of chikungunya, 4380 cases of kala-azar and 101,192 cases of dengue during 2018.” 

Tick Arachnid Parasite Insect Laboratory Tweezers Macro photo Encephalitis Virus or Lyme Borreliosis Disease or Monkey Fever Infectious Dermacentor KFD zoonotic. Image credit: mironovm / 123rf
Ticks are the primary means by which zoonotic diseases such as KFD and lyme disease are spread. Image credit: mironovm / 123rf

Meanwhile, new ones are emerging. “A systematic review of zoonotic diseases in India,” the study states, “concluded that new zoonotic diseases such as cutaneous leishmaniasis, Japanese Encephalitis, leptospirosis, and scrub typhus are spreading to a much wider area at an alarming rate. The reemergence of neglected zoonotic diseases such as KFD can be problematic due to the unavailability of strategies and policies to fight against them.” 

That study notes that India’s efforts to tackle zoonoses include “an active effort to strengthen surveillance for early diagnosis and effective, timely containment. The National Centre for Disease Control plays an important role in strengthening capacity across the country and bringing together epidemiologists, microbiologists, veterinarians, entomologists, etc., to effectively launch required multi-sectorial [sic] action to address zoonotic diseases.” It also highlights that “one of the areas where research is required is behavioral aspects of zoonotic diseases for safe handling of animals by humans.

“This requires a close collaboration between various sectors especially veterinarians and health personnel to put in place effective preventive practices among animal breeders and rearers. There is also a need for strengthening surveillance with a strong laboratory network to pick up diseases both in animals and humans early to launch prompt containment action before an outbreak becomes an epidemic.” 

How best to address zoonoses additionally comes down to tackling our environmental crisis – in particular preserving biodiversity. “Researchers have increasingly raised alarms about the infectious disease risks of biodiversity loss,” said Greenpeace East Asia Forests and Oceans Project Manager Pan Wenjing. “These viruses are naturally isolated away from us by ecosystems that provide a buffer zone. We’re steamrolling right through that ecological buffer. The Chinese government last year took a few decisive steps forward with bans on wildlife breeding and consumption for food. But more needs to be done, in China and elsewhere. Global health crises like the COVID-19 pandemic will happen more often if we fail to protect natural ecosystems globally.” 

As Greenpeace outlines, “along with direct contact with wild animals, the destruction of natural ecosystems facilitates the infectious disease spread through a host of factors. For example, rich biodiversity protects humans from disease transmission from mosquitos because it dilutes large single-species populations. And areas with higher bird diversity showed lower rates of West Nile virus infections because mosquitos, as a vector of infection, were less likely to find suitable hosts. Other examples of infectious diseases increasing because of ecosystem encroachment, include yellow fever, Mayaro, and Chagas disease in the Americas.

“The global scale and rapid rate of natural ecosystem destruction brings increased disease risks. The main causes are direct human encroachment, resource exploitation, and high-intensity agribusiness and industrial agriculture.” 

File:Activities for world environment day in Bhopal (2).jpg. From Wikimedia Commons, the free media repository
A World Environment Day display in Bhopal. Image credit: Suyash Dwivedi [CC BY-SA 4.0 (]
As my colleague Nick Witts of Health Issues India reported earlier this year, environmental degradation has been associated with the outbreak of COVID-19. In India, where environmental degradation has been on an upswing, heeding calls for the 2021-30 period to be the decade of ecosystem restoration is imperative. 

“The COVID-19 pandemic is a result of the degradation of natural areas, species’ loss and exploitation,” said United Nations Environment Programme India Country Office Head, Atul Bagai. “This needs to change. India is already making a concerted effort to reduce carbon dioxide emissions and be part of the global effort to reach net-zero emissions by 2050. India must intensify these efforts to prevent, halt, and reverse the degradation of ecosystems.”

Deforestation Image ID: 115995103 (L) Image credit: max5128 / 123rf. Land diversion article illustration.
Scenes of deforestation pictured in the Himalayas. Image credit: max5128 / 123rf

Deforestation, too, can act in some manner as a disease vector leaving populations exposed to infectious disease, as my colleague Nicholas Parry noted last year. “In India, across the Western Ghats, deforestation is giving rise to higher rates of Kyasanur forest disease (KFD),” he outlined. “KFD is caused by the Kyasanur forest disease virus (KFDV), which is spread to humans by tick bites or through contact with an infected animal, such as a monkey — hence the commonly used name “monkey fever”. 

“The disease is endemic in south Asia and made headlines in Karnataka last year following a KFD outbreak. At the time, lapses in protocol on the part of the state health department concerning vaccination were flagged…Experts found through satellite imagery that areas prone to outbreaks coincided with those that were currently witnessing deforestation. This deforestation typically meant that human activity in the area increased, often bringing farm animals which could also potentially harbour the ticks.” 

Zoonoses are undoubtedly a multifaceted problem and tackling them must incorporate an environmental angle. The costs of neglecting action to tackle them are dire, as the Convention on Biological Diversity notes in stark terms. “Emerging zoonotic diseases threaten human and animal health, economic development and the environment,” they state. “The greatest burden of zoonotic disease is borne by poor people, but emerging infectious diseases impact everyone, with monetary losses of emerging infectious disease much greater in high-income countries. Given that a single zoonotic outbreak can incur trillions of US dollars in costs across the globe, prevention is significantly more cost-effective than response.” 

The World Wildlife Fund (WWF) warns that “today, the risk of another disease jumping from animals to people is higher than ever.” As such, they exhort, “the answers lie in fixing our broken relationship with nature. We have created environments that put all of us at risk. But by taking steps to protect the planet, we can protect people from a future pandemic…Zoonotic diseases are a stark reminder of how people and nature are interconnected. Human activities that encroach upon wild places increase our contact with wildlife and the risk of spillover events. To lower that risk, we must rebalance our relationship with nature.” 

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