Zoonoses and Climatic Change: A Double Threat to Global Health

Zoonoses and Climatic Change: A Double Threat to Global Health

Dhanya Sharma¹* Kumar Shubham²

¹College of Veterinary Science, Khanapara, Guwahati, India

²National Dairy Research Institute, Karnal, Haryana, India

Abstract: Zoonotic diseases are transmitted between animals and humans and are increasingly influenced by climate change. Environmental disruptions elevate the risk of zoonotic transmission. India is particularly vulnerable to climate-sensitive infections, including Nipah virus, Kyasanur Forest Disease (KFD), Chikungunya, Dengue, Malaria, Leptospirosis, Scrub Typhus, Japanese Encephalitis, Anthrax, and Rabies. In response, the Indian government has initiated key programs such as the National One Health Mission 2025, National Animal Disease Control Programme (NADCP), internationally supported Pandemic Fund projects, mobile veterinary services, and public education campaigns. Despite these efforts, significant obstacles remain: delayed detection and reporting of outbreaks, limited disease surveillance infrastructure, insufficient research funding, low levels of public awareness, and inadequate coordination among human health, veterinary, and environmental sectors. To overcome these challenges, emerging veterinarians and engaged citizens need to embrace the “PPR” strategy, Prevention, Preparedness, and Response, guided by the One Health approach. This integrated model is vital for safeguarding animal, human, and ecosystem health against the mounting threat of climate-induced zoonoses.

Keywords: Zoonoses, Climate change, Zoonotic spillover, India, One Health approach

Introduction:

Zoonoses are diseases caused by pathogens like viruses, bacteria, fungi, or parasites that can be transmitted between animals and humans, either directly (via bites, contact, or aerosols) or indirectly (via vectors, food, or water) [WHO, 2023]. Globally, zoonoses are responsible for approximately 60% of all infectious diseases in humans and 75% of emerging infections [NCDC, 2024]. In parallel, climate change is altering biological and ecological systems in ways that increase risk and spread of zoonotic diseases. This dual force creates a global health threat, especially in India with its dense population, rich biodiversity, agricultural dependency, and rapidly changing climate.

How climate change fuels genetic disease spread?

1. A)Habitat Loss and Wildlife Encroachment

When forests dry up or are cut down, wildlife is forced to migrate closer to villages and farms. In Kerala, fruit bats that normally live deep in forests now feed in orchards near homes. This change has been linked to Nipah virus spillovers.

1. B) Vector Expansion
   • Mosquitoes like Aedes spp., ticks, and sandflies thrive in warmer, wetter, or more variable climates.
   • Longer breeding seasons and new geographic rangeslead to wider spread of diseases like Dengue, Chikungunya, Malaria, and Kyasanur Forest Disease (KFD).

1. C) Changes in Animal and Rodent Populations

Rodents are vectors for many diseases. As they thrive in conditions of abundant food and mild winters; erratic rainfall and urban waste allow rodent populations to rise, raising the risk of plague, hantavirus, and leptospirosis.

1. D) Flooding, Extreme Weather, Contamination

Climate-linked extreme weather events such as flooding, droughts, and heatwaves increase the risk of zoonotic diseases. These events also increase waterborne zoonotic illnesses due to contaminated drinking water, like echinococcosis, taeniasis, and toxoplasmosis.

“Zoonotic diseases prevalent in India and their links to climatic factors.”

1.Nipah Virus

Kerala has faced several Nipah outbreaks since 2018, with an increased number of fatalities in July 2025. Fruit bats (Pteropus giganteus), the natural hosts, are moving closer to human settlements due to habitat loss and variable climate.

Recent Trends: Repeated outbreaks in Kerala (2018, 2019, 2021, 2023) with case fatality rates of 40–75%.

2. Kyasanur Forest Disease (KFD/Monkey fever)

Forest ticks of the genus Haemaphysalis spinigera in the Western Ghats transmit KFD. Deforestation and warming temperatures allow the ticks and their small mammal hosts, like monkeys, to move into new regions. Seasonal forest visits by villagers and farmers increase exposure.

3. Dengue, Chikungunya, Malaria

There is an increasing prevalence of both dengue and Chikungunya outbreaks in India, especially in warmer and humid urban and suburban areas. Due to climate change, their spread is further facilitated by more rainfall, warmer and more humid winters, and greater expansion of the Aedes mosquito.

4. Leptospirosis and Scrub Typhus

Following severe monsoons or flooding, there is an increase in cases of Leptospirosis, particularly in Mumbai and the coastal states, due to enhanced interaction between rodents, livestock, and humans. Scrub typhus, which is spread by chigger mites (Trombiculidae), tends to increase during the monsoon months in rural and forested areas, and an increase has also been noted in Rajasthan.

5. COVID19 (SARSCoV2):

Likely emerged via bat reservoir spillover, potentially influenced by habitat disruption, wildlife trade and meat consumption along with climate change affecting bat ecology. India’s genomic surveillance through INSACOG (Indian SARSCoV2 Genomics Consortium) explains the burning issue.

6. Emerging and Neglected Threats: Chandipura, Plague, Q Fever

• Chandipuravirus, a “rabies like” zoonosis linked to sandflies, has caused fatal outbreaks in children in Gujarat.
• Plagueremains a risk where rodent populations surge after climate disturbances.
• Q fever and Brucellosisare also a threat to farmers and veterinarians, and their risk rises with changing climate patterns.

Table 1 summarizes important zoonotic diseases prevalent in our country

Table 1. Major Zoonotic Diseases in India and Their Climate Linkages

Disease	Pathogen / Vector	Reservoir Host(s)	Climate Influence	Key Indian Hotspots
Nipah Virus	Paramyxovirus	Pteropus fruit bats	Forest loss, shifting fruiting seasons, monsoon stress	Kerala, West Bengal
Kyasanur Forest Disease	Flavivirus / Haemaphysalis ticks	Monkeys, small mammals	Warmer, humid microclimates; forest fragmentation	Karnataka, Kerala, Maharashtra
Leptospirosis	Leptospira spp.	Rodents, livestock	Flooding spreads bacteria in water	Maharashtra, Gujarat, Kerala
Dengue & Chikungunya	Flavivirus / Aedes mosquitoes	Humans (amplifying hosts)	Extended breeding in prolonged wet & warm conditions	Nationwide urban & periurban
Scrub Typhus	Orientia tsutsugamushi / chiggers	Rodents	Longer monsoons increase chigger populations	NE India, Himachal, Uttarakhand
Chandipura Virus	Rhabdovirus / sandflies	Small mammals	Vector range expands with hot and dry periods	Gujarat, Andhra Pradesh
Plague	Yersinia pestis	Rodents, fleas	Rodent surges after erratic rainfall and mild winters	Western Rajasthan, Himachal
Rabies	Lyssavirus	Dogs, wild carnivores, bats	Displacement of stray and wild carnivores after floods	Nationwide rural & periurban
Japanese Encephalitis	Flavivirus / Culex mosquitoes	Pigs, water birds	Heavy monsoons and waterlogging increase mosquito density	Uttar Pradesh, Bihar, Assam
CrimeanCongo Hemorrhagic Fever	Nairovirus / Hyalomma ticks	Livestock, ticks	Hot, dry seasons favor tick survival and activity	Gujarat, Rajasthan
Avian Influenza (H5N1/H9N2)	Influenza A virus	Migratory birds, poultry	Climate shifts alter migratory routes; flooding risks	Assam, West Bengal, Kerala
Anthrax	Bacillus anthracis	Livestock, wild herbivores	Droughts and floods expose dormant soil spores	Odisha, Andhra Pradesh, Jharkhand

 

Climate Change Trends & Projections in India

Temperature Increase: The Intergovernmental Panel on Climate Change (IPCC), Geneva, Switzerland has predicted an average temperature rise of 1.5-5.8°C across the globe during the 21st century, with more intense and prolonged heatwaves and erratic rainfall patterns.

Precipitation Variability: More frequent and intense monsoon along with floods and droughts, tend to disturb environmental and socio‑ecological systems.

Forest Ecosystem Stress: Western Ghats and other biodiversity hotspots face drying, habitat manipulation and altered species distributions

Human Displacement & Urbanization: Climate‑forced migration leads to increased density and often poor sanitation conditions increasing risk of zoonotic spillover.

Table 2. Climate Change Mechanisms Driving Zoonotic Spillover

Climate Factor	Ecological Effect	Impact on Zoonotic Diseases	Examples in India
Rising Temperatures	Longer vector breeding cycles; faster pathogen replication	Extended transmission seasons for vectorborne diseases	Dengue, KFD, CCHF
Erratic Monsoon Rainfall	Waterlogging and intermittent dry spells	Increases mosquito and rodent breeding	Dengue, JE, leptospirosis
Floods & Cyclones	Pathogen spread via water; displacement of wildlife	Waterborne and rodentborne outbreaks	Leptospirosis, Anthrax, Rabies
Droughts	Scarce water forces wildlifelivestockhuman interaction	Greater spillover risk from shared resources	Nipah virus, Anthrax
Habitat Loss & Fragmentation	Wildlife encroaches into farms and villages	More frequent humanwildlife contact	Nipah virus, KFD, Avian influenza
Rodent Population Surges	Mild winters and food availability boost reproduction	Rodentborne zoonoses intensify	Plague, Hantavirus, Scrub Typhus
Shifting Migratory Patterns	Birds alter routes and timing due to climate variability	New introduction routes for avian-borne pathogens	Avian influenza (H5N1, H9N2), JE

National Efforts and One Health Approach:

Key initiatives include:

• National One Health Mission (January 1, 2025)aims for cross-sector surveillance and rapid response to zoonoses.
• The National Animal Disease Control Programme (NADCP)seeks to unify surveillance efforts across human, animal, and environmental health sectors, promoting coordinated action for the detection and prevention of zoonotic diseases. Its targeted interventions include controlling brucellosis and foot-and-mouth disease (FMD), administering anti-rabies vaccinations, and implementing sterilization measures for stray dogs.
• G20 Pandemic Fund Projectswith support from the World Bank and WHO and FAO with a fund of USD 25 million (2024–26) to improve lab capacity and genomic surveillance.
• Mobile Veterinary Units and community outreachin highrisk rural and forest areas.

Gaps, Challenges, and Research Needs:

1. Surveillance & Research Gaps

Institutional barriers, funding constraints, and limited awareness and untimely reporting hinder full adoption of One Health practices.

2. Public Awareness & Risk Communication

Poor awareness among at-risk populations limits uptake of preventive measures such as vaccination, vector avoidance, and hygienic practices.

3. Integration Across Sectors

Animal health, human health, forestry, agriculture, environmental agencies, and local governments need stronger coordination in planning and outbreak response.

• Role of Veterinarians and Students –

Prevention, preparedness, and response (P-P-R) for Zoonoses

As veterinarians, we are at the frontline of zoonotic prevention. The risk of disease due to climate change makes our position even more important. We can-

• Monitor and reportunusual animal illnesses early.
  • Educate farmerson safe livestock practices, vaccination, and hygiene.
  • Participate in One Health researchon wildlife, vector, and livestock health.
  • Encourage climate-sensitive animal management, such as sustainable grazing and habitat preservation.In order to minimize spillovers, simple measures like farmer training, rodent control, and vaccination programs can have a significant impact.

India and other nations- a comparative study:

India is highly vulnerable to diseases that spread from animals to humans due to its tropical climate, rich biodiversity, close contact between people and livestock, and frequent extreme weather. The Global One Health Index (GOHI) rates India with a high vulnerability score of about 80 out of 100, but its readiness is low at around 45 out of 100. In comparison, countries like the USA, UK, Australia, and Germany have lower vulnerability scores of 30 to 40 out of 100 and higher readiness scores ranging from 82 to 88 out of 100. This difference is due to better monitoring, coordination across sectors, biosecurity measures, and health systems that can withstand climate challenges. Among its South Asian neighbors, Nepal and Bangladesh face similar vulnerabilities but have weaker monitoring systems. Sri Lanka is slightly less vulnerable. Overall, South Asia is a hotspot for diseases sensitive to climate change, with India at the center of regional spillover risks.

Conclusion

Climate change is making zoonotic diseases more common by disturbing nature, increasing human animal contact, and helping disease carrying insects spread. India is especially at risk because of its large population, diverse wildlife, and frequent extreme weather.

Working together through the One Health approach by protecting animals, people, and the environment is the best way to prevent future outbreaks.

As Rudolf Virchow (1821–1902) who introduced the term zoonoses, thus emphasizing its integrative meaning famously commented,

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