Discuss about emerging zoonotic diseases, their prevalence and effects on animal and human population.

Prevalence of Emerging Zoonotic Diseases

The prevalence of emerging zoonotic diseases is a growing concern globally and particularly in countries like India, which serve as hotspots for their emergence due to diverse ecosystems, high population density, and extensive human-animal interface.

• Global Scenario:
  • Approximately 60% of all known infectious diseases in humans are zoonotic.
  • A staggering 75% of emerging infectious diseases (EIDs) are zoonotic in origin, with most originating from wildlife.
  • The World Health Organization (WHO) estimates that zoonotic diseases cause about 1 billion cases of illness and millions of deaths annually worldwide.
  • Viral zoonoses are particularly concerning, accounting for 75% of emerging infectious diseases.
• Indian Context:
  • India has witnessed several major zoonotic outbreaks, including Nipah virus, Kyasanur Forest Disease (KFD), H1N1 influenza, and COVID-19.
  • A recent analysis of India's Integrated Disease Surveillance Program (IDSP) data (2018-2023) revealed that over 8% of infectious disease outbreaks were zoonotic.
  • Zoonotic outbreaks in India consistently peak during June, July, and August.
  • The Northeast region of India contributed 35.8% of zoonotic disease outbreaks during 2018-2023, followed by the southern (31.7%) and western regions (15.4%).
  • Japanese encephalitis (29.5%), leptospirosis (18.7%), and scrub typhus (13.9%) were the most common zoonotic outbreaks reported under IDSP during this period.
  • The outbreaks of emerging zoonoses like Nipah virus disease, CCHF, KFD, and Zika virus disease have increased in the 2014-2023 period compared to 2009-2013.

Effects on Animal Population

Emerging zoonotic diseases can have devastating effects on animal populations, impacting their health, welfare, productivity, and even biodiversity.

• Direct Health Impacts:
  • Morbidity and Mortality: Many EZDs cause severe illness and death in affected animals. For example, highly pathogenic avian influenza (HPAI) can lead to mass mortality in poultry, and African Swine Fever (ASF) is highly fatal in pigs.
  • Reduced Productivity: Even non-fatal infections can lead to reduced growth rates, decreased milk or egg production, and impaired reproductive performance in livestock, severely affecting agricultural economies.
  • Compromised Animal Welfare: Sick animals suffer, leading to welfare concerns, requiring intensive care, and potentially culling to prevent further spread.
• Economic Impacts on Livestock Sector:
  • Trade Restrictions: Outbreaks can lead to national and international trade bans on live animals and animal products, causing significant economic losses for farmers and industries.
  • Culling and Depopulation: Large-scale culling of affected or exposed animals is often necessary to control outbreaks, resulting in direct financial losses for farmers.
  • Increased Costs: Higher costs for surveillance, diagnostics, vaccinations, biosecurity measures, and treatment further burden the animal husbandry sector.
• Wildlife and Biodiversity Impacts:
  • Wildlife Mortality: EZDs can decimate wild animal populations, affecting ecosystem balance. For instance, Kyasanur Forest Disease primarily affects monkeys.
  • Conservation Concerns: The introduction of pathogens from domestic animals or humans can threaten endangered wildlife species.
  • Ecosystem Disruption: Changes in wildlife populations due to disease can have cascading effects on food webs and overall ecosystem health.

Effects on Human Population

The impacts of emerging zoonotic diseases on human populations are far-reaching, affecting public health, economic stability, social structures, and global security.

• Public Health Impacts:
  • Morbidity and Mortality: EZDs cause widespread illness, hospitalizations, and deaths, exemplified by the COVID-19 pandemic, Ebola, and Nipah virus outbreaks.
  • Healthcare Burden: Outbreaks strain healthcare systems, requiring significant resources for diagnosis, treatment, critical care, and public health responses.
  • Long-term Health Consequences: Some zoonoses can lead to chronic health issues, disabilities, and reduced quality of life in survivors.
  • Antimicrobial Resistance (AMR): The widespread use of antibiotics in animals contributes to the development of drug-resistant pathogens, complicating treatment in humans.
  • Mental Health Impacts: Pandemics and outbreaks can cause widespread anxiety, fear, and psychological distress among populations.
• Socio-economic Impacts:
  • Economic Losses: Global pandemics like COVID-19 have caused trillions of dollars in economic losses due to lockdowns, disrupted supply chains, reduced productivity, and trade impacts.
  • Livelihood Disruption: Farmers, livestock workers, and those dependent on animal-related industries face severe income losses and livelihood destruction during outbreaks.
  • Food Security: Diseases affecting livestock can impact food production and availability, threatening food security, especially in vulnerable communities.
  • Travel and Tourism: Outbreaks often lead to travel restrictions and a decline in tourism, affecting entire industries and national economies.
  • Social Disruption: School closures, social distancing measures, and restrictions on public gatherings disrupt social life and community functions.
• Global Health Security Threats:
  • Pandemic Potential: Many EZDs have the potential to cause global pandemics, as demonstrated by COVID-19, posing an existential threat to global health security.
  • Inequity: Resource-poor communities and low-income countries often bear a disproportionate burden of zoonotic diseases due to weaker surveillance and response systems.
  • Geopolitical Instability: Widespread disease outbreaks can exacerbate existing social and economic inequalities, potentially leading to instability.

Factors Driving Emergence and Spread

The increasing incidence of emerging zoonotic diseases is driven by a complex interplay of environmental, societal, and biological factors:

• Environmental Degradation and Land Use Change: Deforestation, agricultural expansion, and human encroachment into natural habitats increase contact between humans, livestock, and wildlife, facilitating pathogen spillover.
• Climate Change: Alters the distribution of disease vectors (like mosquitoes and ticks), hosts, and pathogens, expanding the geographic range of diseases and creating new transmission pathways.
• Globalization and Travel: Increased international travel and trade facilitate the rapid global spread of pathogens, as seen with SARS-CoV-2.
• Agricultural Intensification: Crowded animal populations in industrial farming settings can act as reservoirs for pathogens and accelerate their evolution and transmission.
• Urbanization and Population Growth: Densely populated urban areas can amplify disease transmission, and informal settlements often lack adequate sanitation, increasing risk.
• Wildlife Trade and Consumption: Wet markets and the trade in exotic animals create opportunities for novel pathogens to jump species barriers.
• Antimicrobial Misuse: Inappropriate use of antibiotics in both human and animal health contributes to the rise of drug-resistant strains, making diseases harder to treat.

The interconnectedness of human, animal, and environmental health highlights the indispensable role of a 'One Health' approach for integrated surveillance, early detection, rapid response, and sustainable prevention strategies against emerging zoonotic diseases.