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Listen to Story In the post-Covid-19 era, scientists remain on high alert for infections emerging from every corner of the world. After bird flu began annihilating millions of animals in the UK, US, Australia, Antarctica and the sub-Antarctic islands, in 2021, several variants of H5N1 emerged, including the less virulent H9N2 strain in India's West Bengal. Meanwhile, mpox, earlier known as monkeypox , made headlines for its global spread in 2022.
These viruses, which were first found in animals, have now successfully jumped to humans, transmitting newer infections, the nature of which is keeping scientists on their toes. WHAT IS THIS PHENOMENON? This phenomenon of animal-to-human transmission is known as zoonoses and the diseases are called zoonotic diseases. These infections are caused by a pathogen, which could be bacteria, virus, fungi or parasites that jump from animals to humans in close contact.
The most common zoonoses have been Ebola, and salmonellosis, which have shown recurring outbreaks. Some diseases, such as HIV, which began as a zoonosis, later mutated into human-only strains. The latest in the least of similar transmission are mpox, bird flu and the SARS-C0V-2 that led to the Covid-19 pandemic.
These illnesses are increasingly becoming a public health concern, especially with the rising interaction between humans and animals. After bird flu began annihilating millions of animals across the globe. (Photo: AFP) Microbiologist Dr Varsha Shridhar, who specialises in infectious diseases and Director and Co-founder of Molecular Solutions Care Health spoke about the causes and implications of zoonotic diseases, and how climate and public health preparedness can combat them.
According to Dr Shridhar, zoonotic diseases can originate from a wide range of animal hosts, including bats, birds, and even mammals. "In the last 20-25 years, we've noticed that many of the severe infections in humans come from animals. The pathogens may not cause significant harm to their natural animal hosts but can lead to severe outbreaks when they infect humans," Dr Shridhar told IndiaToday.
in. One of the most well-known zoonotic diseases is HIV (Human Immunodeficiency Virus), which originated in monkeys and apes as a virus called SIV. While these animals carry the virus without much harm, the virus made a "jump" to humans, likely through activities such as the consumption of bushmeat, leading to the global HIV/AIDS epidemic.
Similarly, other zoonotic diseases, such as SARS and Covid-19, have had devastating global impacts. WHY ARE ZOONOTIC DISEASES ON THE RISE? Zoonotic diseases are not new. They have been around for centuries.
However, Dr Shridhar pointed out that human activities are increasingly exacerbating the spread of these diseases. "Deforestation, industrialisation, and increased human interaction with animals are creating more opportunities for pathogens to leap from animals to humans," she explained. Other zoonotic diseases, such as SARS and Covid-19, have had devastating global impacts.
(Photo: Getty Images) As human populations expand into animal habitats, the chances of coming into contact with potential zoonotic pathogens rise. THE ROLE OF CLIMATE AND HUMAN IMPACT Climate change is another major factor contributing to the spread of zoonotic diseases. The destruction of natural habitats, changes in weather patterns, and the extinction of certain animal species all play a role in destabilising the delicate balance between humans, animals, and the environment.
Dr Shridhar cited the example of the 1918 influenza outbreak, where disrupted bird migrations due to unusual weather patterns facilitated the spread of the deadly H1N1 virus (swine flu). Not all diseases transmitted by animals are considered zoonotic. For example, while malaria and dengue are transmitted to humans via mosquitoes, they are classified as vector-borne diseases, not zoonotic.
Zoonotic diseases, on the other hand, must meet two criteria: they originate in animals, and once they infect humans, they can be transmitted from person to person. SARS-CoV-2, the virus responsible for Covid-19, is an example of a zoonotic disease that meets both criteria. Dr Varsha pointed out the broader issue of biodiversity loss and environmental degradation as key factors in the rise of zoonotic diseases.
"When we destroy ecosystems, we increase our exposure to animals and insects that carry diseases," she said. The impact of climate change on disease transmission is a reminder of how interconnected the health of humans, animals, and the environment truly is. HOW CAN WE STAY SAFE? While zoonotic diseases are a global issue, Dr Shridhar stressed that people can take certain steps to protect themselves.
" Practising good hygiene , such as washing your hands regularly and keeping your surroundings clean, is essential," she said. While this advice may seem simple, she acknowledged that it can be difficult for many people, particularly those living in poverty or without access to clean water and sanitation. Mpox disease causes blisters in the hands.
(Photo: Reuters) The microbiologist encouraged people to be mindful of their interactions with animals, particularly in areas where zoonotic diseases are common. She also highlighted the importance of a healthy lifestyle, including eating nutritious food and maintaining a clean living environment , to boost immunity and reduce the risk of infections. NEED FOR PUBLIC HEALTH PREPAREDNESS On a larger scale, Dr Shridhar emphasised the importance of public health systems in tackling zoonotic diseases.
"Surveillance plays a crucial role in identifying outbreaks early, but integrating data from different sources, human, animal, and environmental, is key," she said. Precision Health, a platform that Dr Shridhar is involved with, enhances public health preparedness by collecting and analysing data from various sectors to predict and prevent future outbreaks. Public health systems also need to become more responsive to local conditions.
"We need a dual strategy that incorporates both bottom-up and top-down approaches. Local communities should be empowered to provide data, which can then inform targeted interventions at the grassroots level," she said. Zoonotic diseases pose a growing threat to global health and both individual actions and systemic changes are needed.
By improving hygiene, supporting environmental conservation, and strengthening public health systems, we can reduce the risk of zoonotic outbreaks and create a safer world for future generations..
