Mpox, Nipah virus, bird flu: Why are zoonotic diseases on the rise?

The rapid spread of a new strain of mpox, formerly called monkeypox, triggered the World Health Organization (WHO) to declare it a ‘public health emergency of international concern' in August. The viral disease, which has mainly affected Africa, has also been reported in other countries. India reported its first mpox case last week, although it was declared an isolated case with no link to the new strain of the virus.

Mpox is a zoonotic disease that can spread from animals like monkeys to humans. Similarly, other zoonotic diseases have also affected public health in recent times. Nipah, Zika and Chandipura viruses, which wreaked havoc in India and other parts of the world in the past few months, can all spread from animals to humans. Cases of avian influenza (bird flu) have also been reported in humans.

Given the severe health concern zoonotic diseases pose, mid-day.com speaks to Dr. Rituja Ugalmugle, Internal Medicine, Wockhardt Hospitals, and Dr. Disha Padalkar, Consultant Pediatric Infectious Diseases, Ankura Hospital for Women and Children, Pune, who decode why infections are spreading from animals to humans, the possible implications of this trend and steps that can be taken to prevent this public health concern.

What are zoonotic diseases?
Ugalmugle: Zoonotic diseases are infections caused by bacteria, viruses or parasites that spread between animals and humans. They can result from direct contact, through contaminated food or water or via vectors like mosquitoes. Common examples include rabies, avian influenza (bird flu) and Covid-19.

Padalkar: As per WHO, zoonotic disease is any infection that is naturally transmissible from vertebrate animals to humans.

How do viruses transmit from animals to humans?
Ugalmugle: Viruses transmit from animals to humans through direct contact with infected animals, consumption of contaminated animal products or exposure to vectors like ticks or mosquitoes. Sometimes, viruses mutate to infect humans, as seen with SARS, MERS and Covid-19, enabling human-to-human transmission.

Padalkar: Viruses can transmit from animal to humans by direct, indirect contact or through insect vectors. Direct contact can occur through an infected animal's bodily fluids such as blood, saliva, urine etc. An example is rabies infection. Indirect contact can occur by touching contaminated soil or feed and then touching your face, mouth or eyes. Viruses are also transmitted to humans through insect bites after the insect has fed on an infected animal.

Why have there been rising instances of zoonotic diseases in recent times, especially after the Covid-19 pandemic?
Ugalmugle: The rise in zoonotic diseases post-COVID-19 may be due to increased human-animal interactions, habitat destruction and intensive farming practices. Globalisation and climate change also contribute, creating environments where pathogens can jump between species more easily and spread more rapidly.

Padalkar: Emerging infectious diseases are diseases that have newly appeared in a population or have existed but are rapidly increasing in incidence. As per various studies, 60-70 per cent of them are zoonotic diseases. These are slowly increasing in number in the last half-century. After COVID-19, these are being reported and getting attention.

A new outbreak of zoonotic diseases continues to occur as the human-animal interface grows. Destruction of animal habitats and human population sprawl increases contact between human and wild animals. Studies have shown a rise in the incidence of these diseases, particularly in tropical, bio-diverse areas.

Also Read: Mpox: Mumbai doctors highlight why the viral disease is deadly

Does climate change play a role in the spread of zoonotic diseases?
Ugalmugle: Yes, climate change influences the spread of zoonotic diseases by altering animal migration patterns, increasing vector populations (e.g., mosquitoes) and disrupting ecosystems. Warmer temperatures can extend the range of disease-carrying insects and force wildlife into closer contact with humans, increasing transmission risks.

Padalkar: The availability of suitable vectors is a precondition for the emergence of new zoonotic diseases. Climate change has catastrophic effects on human, animal and environmental ecosystems. It can also result in human socio-demographics and migration. The complex interaction between climate change and ecosystem disturbance along with exposure to vector insects or wild animals results in the emergence of zoonotic diseases.

What are the possible implications of this trend?
Ugalmugle: The rise in zoonotic diseases threatens global public health, leading to new pandemics, overwhelming healthcare systems and economic strain. In the long term, frequent outbreaks may weaken immune systems, increase antibiotic resistance and create a need for rapid medical advancements to combat emerging diseases.

Padalkar: Emerging zoonotic infectious diseases affect human health in different ways. These long-term outcomes include the pandemic (Covid-19), recurring outbreaks (Ebola virus disease), neurological effects (Nipah virus can cause neurological effects in survivors) and sometimes it might result in antibiotic resistance. On a large scale, they can cause economic losses and public health burdens.

Do zoonotic diseases affect children differently?
Padalkar: Children have immature immune systems. Hence, sometimes zoonotic diseases can affect them differently. They have a higher risk of contracting disease. The severity of the diseases may also vary in children. For example, the Covid-19 infection was not that severe in children as compared to the adult population. In contrast, the recent outbreak of Chandipura virus infection in 2024 in the western and central parts of India affected children under 15 years with death in 33 per cent of infected children.

Also Read: Chandipura virus: Know all about the infection that has claimed children's lives in Gujarat

How can one contain or prevent the spread of zoonotic diseases?
Ugalmugle: Preventing zoonotic disease spread involves reducing human-wildlife contact, ensuring proper sanitation in livestock practices and controlling vector populations. Public education, vaccinations, safe food handling and maintaining healthy ecosystems are essential measures. Monitoring wildlife health and early detection systems can help mitigate outbreaks.

Padalkar: Zoonosis involves the interaction of humans, animals and the environment. Hence multi-sectoral measures are necessary to ensure effective control. The following precautions are required to prevent this.
• Surveillance is crucial to prevent and control zoonotic diseases. Identification of "hot-spot areas" and monitoring is necessary. All potential sources such as exotic animals and birds need to be subjected to surveillance.
• There's a need for mass campaigning to increase public awareness about such diseases.
• Ensure safe food production of animal origin.
• Some zoonoses spread through vectors like mosquitoes, ticks and lice. Hence, successful vector control strategies are necessary.
• Ensure safe infectious disease testing laboratories to avoid the accidental spread of zoonotic diseases.

Disclaimer: This content is for informational purposes only and should not be considered professional medical advice.