Crossing borders: Tracking the spread of zoonotic diseases

Bengaluru: India is grappling with a deepening public health challenge, driven by shifting climate patterns and rising ecological disruptions. Zoonotic diseases, once sporadic and geographically contained, are now spreading across borders with greater speed and reach, threatening the health of both humans and animals and testing the limits of the country’s healthcare systems.

According to the World Health Organisation (WHO), zoonoses constitute a large percentage of new and existing diseases in humans across the world. A recent report by the World Organisation for Animal Health (WOAH) shows that 47% of global animal disease outbreaks between 2005 and 2023 were zoonotic, that is, infectious diseases that are naturally transmissible from animals to humans and can spread amongst human beings. The impact of such diseases has been stark in India.

Each year, India reports a steady increase in cases of zoonotic diseases, accompanied by high mortality and morbidity rates. These efforts to control the outbreaks are hindered by fragmented responses, an overburdened healthcare system, and a lack of coordinated, actionable strategies to effectively address the issue.

The Covid-19 (SARS-CoV-2) pandemic, which originated due to a zoonotic spillover event (transmission of pathogens from wild animals to human beings), had a devastating impact on people across India. 

Between January 31, 2020 and December 31, 2024, a total of 4.5 crore Covid-19 cases and 5.33 lakh deaths were reported, according to the Ministry of Health and Family Welfare dashboard. 

Other animal-borne diseases, such as dengue and rabies, also pose a significant public health threat. India accounts for 36% of the world’s rabies deaths. Dog bites remain the primary cause of human rabies. 

In Karnataka, dog bite cases have been steadily increasing. According to data from the Integrated Disease Surveillance Programme (IDSP), there were 1.63 lakh cases in 2022, 2.32 lakh in 2023, and 3.61 lakh in 2024.

In the same year, Karnataka reported 42 rabies-related deaths, a sharp rise compared to the single-digit figures recorded in previous years. This spike is partly attributed to Karnataka’s decision to make rabies a notifiable disease in December 2022.

Telangana reported zero suspected human rabies fatalities from 2022 through January 2025, but dog bite incidents remain alarmingly high. Telangana experienced its worst year for seasonal diseases in 2024, recording 10,077 confirmed dengue cases alongside 13,592 suspected chikungunya cases. 

Andhra Pradesh documented 2,45,174 dog bite cases in 2024, while Telangana recorded 1,21,997 cases during the same period. 

Dengue cases have also surged across several states. According to the Department of Health, Government of Karnataka, over 32,000 dengue cases were reported in 2024. More than half of these were recorded in Bengaluru. 

In Tamil Nadu, dengue has emerged as the most concerning vector-borne disease. In 2024, the state reported 26,740 cases and 13 deaths. This marks a significant increase since the 2017 outbreak, which saw 23,035 cases and 63 deaths. 

Other zoonotic diseases, including leptospirosis, scrub typhus and encephalitis, also saw an increase in 2024 compared to 2023.

Since the 2018 Nipah outbreak in Kerala, which claimed 20 lives in Kozhikode, the virus has been recurring every year, mostly in the northern districts of the state. 

Mosquito-borne illnesses typically surge during monsoon and post-monsoon periods, affecting urban and rural populations alike.

Why are we seeing this rise? 

A senior researcher, who works for the National One Health Mission, notes that the spread of animal-borne diseases is attributable to various factors, including climate change, rapid and unplanned urbanisation, fragmentation of forest area, close animal-human interaction and increased disease surveillance. India launched the National One Health Mission (NOHM) in 2022 to address health challenges and reduce the burden of zoonotic diseases. 

For instance, deforestation and land-use change in the Western Ghats have brought humans into closer contact with wildlife. Here, there is a risk of contracting the Kyasanur Forest Disease (KFD) through tick vectors, says Swetavalli Raghavan, advisor to the Karnataka government on Antimicrobial Resistance (AMR). “In urban areas, inadequate sanitation, stagnant water, and animal waste facilitate the spread of resistant microbes, particularly, in densely populated areas,” she says.

There is a noticeable pattern in the rise of viral infections, many of which are zoonotic, spreading from animals to humans and, in some cases, further through human-to-human transmission, notes Dr Ishwar Gilada, a Mumbai-based expert in infectious diseases.

“Over the past four decades, we have seen repeated outbreaks and epidemics caused by zoonotic viruses. These patterns suggest that the human race remains at constant risk of major health crises, driven by ongoing interactions and conflicts between humans, animals, and birds,” he tells DH. 

Monitor and control

The need to monitor and control outbreaks in the poultry population in case of H5N1 is all the more important, in addition to avoiding over-intrusion in animal habitats, Dr Gilada says.

“We also commonly see Respiratory Syncytial Virus (RSV) and Human Meta-Pneumo Virus (HMPV) infections. Influenza A also causes Avian flu, Swine flu, Equine flu, Canine flu and Bat flu, among others,” says Dr Gilada.

According to Dr V Ramankutty, a well-known public health expert from Kerala, contamination of waterbodies and lapses in garbage disposal could be possible reasons for the increasing number of communicable diseases and animal-borne diseases.

“To give more emphasis on preventing the outbreak of such diseases along with curing, an efficient team needs to be built up and doctors should be given career incentives for carrying out research and studies on preventive measures,” he says.

It could also be true that advancements in medicine are helping in the detection of infections like amoebic meningoencephalitis, he added. “More focus should be given to prevention rather than cure. Services of ICMR-National Institute of Epidemiology in Chennai should be more effectively utilised,” Dr Ramankutty adds.

Way forward

The NOHM focuses on integrated disease surveillance, strengthening laboratories, and promoting research and development of diagnostics, therapeutics, and vaccines for priority diseases. It also aims to build capacity through professional training, improve data and information sharing, and engage communities in disease prevention efforts.

The country’s first One Health institute, coming up in Nagpur, will focus on human, animal and environmental health, tracking diseases across human beings, animals and the environment to enable early detection.

As many as 20 research projects worth Rs 23.37 crore, conducted by research institutes such as Indian Council of Agricultural Research and the Indian Institute of Science, are being funded under NOHM. In 2024, an Indian Council of Medical Research study on select slaughterhouses in Punjab, Assam and Telangana was launched, aiming to build a real-time surveillance model for detecting zoonotic diseases among slaughterhouse workers, with a budget of Rs 13.75 crore over three years.

There are also Central projects on pan-India syndromic surveillance for four major respiratory viruses — SARS-CoV-2, RSV, HMPV, and Nipah — across 73 sites, and an Acute Encephalitis Syndrome surveillance, according to the senior One Health researcher.

Karnataka has established a One Health Taskforce, bringing together experts from public health, animal husbandry, wildlife, and environment departments. Bengaluru is one of the pilot sites for a One Health surveillance initiative (led by the One Health Trust and the National Centre for Biological Sciences), which monitors zoonotic pathogens and resistance genes in animals, humans and environmental samples.

Swetavalli Raghavan advises the establishment of a statewide “One Health Surveillance Grid” – a digital, real-time dashboard linking hospitals, veterinary clinics, and environmental labs to track zoonotic diseases, AMR hotspots, and vector presence, to power predictive mapping and early warning alerts for outbreaks.

Additionally, expanding urban surveillance to monitor sewage and river water in Bengaluru, Mangaluru, and Mysuru for resistant genes and zoonotic pathogens will help identify emerging health threats early, before clinical symptoms appear in humans, she says.

Implementation 

The issue lies in the implementation of the One Health approach. “Across the world, we are used to working in silos. One Health challenges us to work in less siloed ways,” says Dr Prashanth N Srinivas, director, Institute of Public Health, Bengaluru, pointing out KFD as an example.

“What we do before and between outbreaks matters, not just developing and administering vaccines. The geographic reach of the disease (KFD) is increasing. We need to step up surveillance on birds, cattle, and wild animals, besides humans. The forest department, and human and veterinary health workers must all do surveillance and have a common pool of data to collaborate. This has not been institutionalised yet,” he says, emphasising data sharing and collaboration at panchayat, district and state levels.

Highlighting how land use change is an important reason for the number of disease cases going up, he calls for ecological countermeasures to prevent pathogen spillovers and pandemics. “We have to put a stop to sudden massive land use changes in forests.”

In April this year, a comprehensive research project estimated at Rs 19 crore was launched, aiming to develop a real-time surveillance model to detect and diagnose zoonotic diseases in bird sanctuary workers and nearby residents. 

With India being a vital hub along the Central Asian migratory bird flyway, bird sanctuaries represent an area where the risk of zoonotic transmission is heightened. Sanctuary workers, including rescue teams and veterinarians, are especially vulnerable due to their close proximity to wild and migratory birds.

A study on bird-human interaction and a surveillance system for zoonotic spillovers will be conducted by ICMR in select bird sanctuaries and wetlands across Sikkim, Maharashtra and Tamil Nadu. It will involve periodic sampling of birds and environmental specimens to screen for emerging pathogens, utilising advanced diagnostic tools like Next Generation Sequencing (NGS) for the early identification of novel infections.

(With inputs from Arjun Raghunath in Thiruvananthapuram, Mrityunjay Bose in Mumbai, E T B Sivapriyan in Chennai, S N V Sudhir in Hyderabad, Sumir Karmakar in Guwahati)