In the light of recent surge in incidence of zoonotic diseases, discuss in detail about the zoonotic diseases and their management in India.
Infectious animal diseases are spreading to previously unaffected regions and species, with nearly half (47 per cent) capable of zoonotic transmission or spreading between animals, according to the inaugural State of the World’s Animal Health report released by the World Organisation for Animal Health (WOAH) on May 23, 2025.
Increasing distribution and intensity of diseases such as African Swine Fever (ASF), avian influenza, foot and mouth disease (FMD) and peste des petits ruminants (PPR) was highlighted by the report, warning that their proliferation was destabilising agrifood systems. These disruptions threatened global food security, public health and biodiversity.
Zoonotic diseases:
- The word ‘Zoonosis’ (Pleural: Zoonoses) was introduced by Rudolf Virchow in 1880 to include collectively the diseases shared in nature by man and animals. Later WHO in 1959 defined that Zoonoses are those diseases and infections which are naturally transmitted between vertebrate animals and man.
- Zoonoses may be bacterial, viral, or parasitic, or may involve unconventional agents.
Classification of zoonotic diseases:
According to the Etiological (Originating) Agents
- Bacterial zoonoses: e.g. anthrax, brucellosis, plague, leptospirosis, salmonellosis, lyme disease
- Viral zoonoses: e.g. rabies, arbovirus infections, KFD, yellow fever, influenza
- Rickettsial zoonoses: e.g. murine typhus, tick typhus, scrub typhus, Q-fever
- Protozoal zoonoses: e.g. toxoplasmosis, trypanosomiasis, leishmaniasis
- Helminthic zoonoses: e.g. echinococcosis (hydatid disease), taeniasis
- Fungal zoonoses: s e.g. deep mycosis – histoplasmosis, cryptococcosis
- Ectoparasites: e.g. scabies, myiasis
According to the mode of transmission
- Direct zoonoses: Transmitted from an infected vertebrate host to a susceptible host (man) by direct contact, by contact with a fomite or by a mechanical vector. Eg: rabies, anthrax, brucellosis etc.
- Cyclozoonoses: Require more than one vertebrate host species, but no invertebrate host for the completion of the life cycle of the agent, e.g. echinococcosis, taeniasis.
- Metazoonoses: These are transmitted biologically by invertebrate vectors, in which the agent multiplies and/or develops and there is always an extrinsic incubation (prepatent) period before transmission to another vertebrate host e.g., plague.
- Saprozoonoses: These require a vertebrate host and a non-animal developmental site like soil, plant material, pigeon dropping etc. for the development of the infectious agent e.g. aspergillosis.
According to the reservoir host
- Anthropozoonoses Infections: Transmitted to man from lower vertebrate animals e.g. rabies, leptospirosis, plague, arboviral infections, brucellosis and Q-fever.
- Zooanthroponoses Infections: Transmitted from man to lower vertebrate animals e.g. streptococci, staphylococci, diphtheria, enterobacteriaceae, human tuberculosis in cattle and parrots.
- Amphixenoses Infections: Maintained in both man and lower vertebrate animals and transmitted in either direction e.g. salmonellosis, staphylococcosis.
Factors Influencing Prevalence of Zoonoses
Ecological changes in man’s environment
- Exploitation of new territories and natural resources like harnessing the power of rivers, constructing roads and pipelines through thinly populated areas, clearing, irrigating and cultivating new land, deforestation lead to entering of humans in the unaccustomed ecosystem in which potential pathogens form part of the biotic community (natural focus).
- Large scale expansion of agricultural and engineering resources, construction of dams, artificial lakes, irrigation schemes, clearing of forests -all these lead to changing of the biting habits of the blood sucking vectors and alteration in the population of reservoir animals which has led to the spread of such diseases.
- Handling animal by-products and wastes (occupational hazards). For eg- anthrax in carpet weavers, live stock raisers and workers with animal hair in the textile industry, leptospirosis in rice field workers, listeriosis in agricultural workers etc.
- Increased movements of man: Land development, engineering project work, pilgrimages, tourism, etc. expose the people to contaminated food and water.
- Increased trade in animal products: Wool, bone meal, meat, etc. from an area where some of the zoonoses are endemic, are likely to introduce the disease into new territories.
- Transportation of virus infected mosquitoes: Eg- Aircraft, ship, train, motor and other vehicles bring the viruses in to a new area, e.g. yellow fever Chikungunya fever, dengue fever etc.
- Cultural anthropological norms: For eg- in Kenya, people allow the dogs and hyenas to eat human dead bodies infected with hydatidosis. This helps to perpetuate the transmission cycle of the disease.
Current surge in zoonotic diseases around the world:
- Avian influenza, also known as bird flu or highly pathogenic avian influenza (HPAI), had devastated bird populations over the past two decades, causing the loss or culling of more than 630 million birds. In 2024 alone, the virus affected new regions and species, including mammals.
- In a notable shift, more countries reported HPAI outbreaks in non-poultry species (55) than in poultry (42). A total of 2,570 non-poultry outbreaks and 943 poultry outbreaks were recorded. Particularly concerning was the doubling of outbreaks in mammals, to 1,022 in 2024 from 459 in 2023, raising alarms about cross-species transmission and potential adaptation to humans.
- Bluetongue virus: A total of 3,626 bluetongue outbreaks were reported by 24 countries. It is a viral disease that affects ruminants like sheep, cattle and goats, spread by tiny biting midges.
- FMD: 18 countries reported a total of 216 outbreaks, including 29 exceptional epidemiological events. Germany experienced its first FMD outbreak since 1988 and EU’s first since 2011. Meanwhile, a zone within South Africa recorded the first occurrence of serotype SAT 3, while Iraq and Kuwait have reported the first occurrence of serotype SAT 1 in the country or zone.
- Lumpy skin disease: 319 outbreaks were reported from 11 countries, including 11 exceptional epidemiological events. The disease was detected for the first time in northern Africa, with outbreaks reported in Algeria, Libya, and Tunisia, as well as Japan. It also reoccurred in Eastern and Southern Asia.
- New World screwworm: 8,363 outbreaks were reported by seven countries, involving 13 exceptional epidemiological events. The disease was detected for the first time in Mexico in December 2024, while it reoccurred in Nicaragua, which accounted for over 60 per cent of the reported outbreaks. Other affected countries included Belize, Costa Rica, El Salvador, Guatemala and Honduras.
- Peste des petits ruminants: Once confined to the Global South, PPR recently re-emerged in Europe, with outbreaks in Greece, Romania, and Bulgaria in 2024 and in Hungary in January 2025. Despite years of progress in PPR control the disease spread to regions previously free of the disease, prompting serious concern and increased vigilance among veterinary authorities.
Zoonotic Diseases and India
- India is among the top geographical hotspots where zoonotics diseases are a major public health issue causing high burden of morbidity and mortality.
- High priority zoonotic diseases like Brucellosis have emerged from Haryana to Goa, incidence and prevalence of occupational zoonotic disease like Anthrax have affected human health throughout.
- Similarly, Bovine tuberculosis (bTB) is a chronic disease of cattle that impacts productivity and represents a major public health threat and is considered endemic in India.
- Further, being among the highest bacterial disease burden in the world, antibiotics, therefore, have a critical role in limiting morbidity and morality and consequently Antimicrobial Resistance (AMR) has huge implications for India.
- Major public health zoonotic diseases in India include Rabies, Brucellosis, Toxoplasmosis, Cysticercosis, Echinococcosis, Japanese Encephalitis (JE), Plague, Leptospirosis, Scrub typus, Nipah, Trypanosomiasis, Kyasanur forest disease (KFD) and Crimean-Congo haemorrhagic fever (CCHF).
- According to the National Centre for Disease Control (NCDC), about 75% of emerging and re-emerging infections are zoonotic, and new pathogens (viruses) continue to emerge and spread across countries.
Measures Taken to Control Zoonotic Diseases
Following Programmes have been launched under National Centre for Disease Control:
- Integrated Disease Surveillance Programme (IDSP)
- National Programme for Containment of Anti-Microbial Resistance
- National Viral Hepatitis Surveillance Programme
- Strengthening Inter-sectoral coordination for prevention and control of Zoonotic Diseases of Public Health Importance
- National Rabies control programme
- Programme for prevention and control of Leptospirosis
To limit the spread of highly damaging diseases like avian influenza, FMD and PPR, the global community must strengthen international cooperation and ensure equitable access to safe, effective vaccines, alongside other control measures.
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