Dear Editor,

Animals have played a significant part in human evolution. Henceforth, human and animal habitat sharing expanded, paving the way for the emergence of zoonotic illnesses.1 Zoonosis is defined as any illness or condition that can naturally spread from vertebrate animals to humans. More than 200 zoonoses are recognized in the world, which poses a severe threat to public health.2 The epidemiology of the following six zoonotic diseases— scrub typhus, leptospirosis, cutaneous anthrax, brucellosis, Lyme disease and Crimean Congo Haemorrhagic Fever—is evolving in India. 

Scrub typhus: It is caused by the bacterium Orientia tsutsugamushi, transmitted to humans through the bite of infected chigger mites. Rodents serve as the primary reservoir. The mites become infected when they feed on these rodents. In South India, the illness manifests usually during the winter months, while in the north, the peak occurs in post-monsoon, exhibiting seasonality.3,4 This disease, earlier known to be restricted to rural habitats, is currently reported from a variety of habitats ranging from hills to plains, forests to desert, agricultural to dry lands, and rural to urban areas.5 

Leptospirosis: It is caused by spirochete Leptospira, transmitted from animals to humans through primarily direct contact with the urine of infected animals, sometimes indirectly with the contact with water, soil, or food contaminated with the urine of infected animals. It is linked to substantial morbidity and mortality. Due to factors such as animal husbandry, unplanned urbanization, severe monsoons, and an agrarian lifestyle, the disease is most prevalent in southern, central, and eastern India. Many instances are recently recorded in northern part such as Uttar Pradesh, Gujarat, and Maharashtra.6 

Cutaneous anthrax: Bacillus anthracis is the causative agent of cutaneous anthrax, a zoonotic illness that typically appears following direct contact with animals or animal products contaminated with the disease.7 Herbivorous animals, such as cattle, sheep, and goats, are typically infected and eventually killed by the epizootic disease anthrax. It would not take long for anthrax to become recognized entirely as an enzootic illness in a given area, where the zoonotic transmission will likely start, and human cases will likely surface, posing a severe threat to public health.8

Brucellosis: It is caused by bacteria of the genus Brucella. It primarily affects animals but can be transmitted to humans, typically through direct or indirect contact with infected animals or their products. Human brucellosis has a general incidence of 17–34% in India.9 Both its prevalence and spread are influenced by procedures used to produce milk and milk products and animal husbandry techniques.10

Lyme Disease: This anthropo-zoonotic disease is transmitted by an arthropod vector and is caused by many genospecies of the pathogenic spirochete Borrelia burgdorferi. The primary method of human transmission is by tick (Ixodes spp.) bite. Reports of instances of Lyme disease in India have come from Himachal Pradesh, Haryana, Bihar, Uttarakhand, Uttar Pradesh, Maharashtra, and some regions of south India. Northeastern Indian states have reported a 13% seroprevalence of Borrelia-positive cases. There have also been reports of Ixodes ticks in the Himalayan region.11

• Crimean Congo Hemorrhagic fever (CCHF): It is caused by the CCHF virus (CCHFV). It is transmitted to humans by nosocomial infection, tick (Hyalomma) bites, crushing ticks with bare hands, and contact with infected animals or people’s blood or bodily fluids.12

The following factors influence the changing epidemiology of zoonotic diseases in India.

• Urbanization and deforestation: A higher population density encourages deforestation. There is a decline in the “recorded forest area” in the tribal districts, which account for 60% of all forests in India.13 These factors contribute to the emergence and reemergence of zoonotic diseases originating in arthropods and rodents, including leptospirosis, dengue, and japanese encephalitis, because of the disruption of the natural habitat of wildlife and increased breeding grounds for vectors.14
• Vector genetics and competence: Viral adaptability to individual hosts and their ability to increase are caused by genetic reassortment, genetic recombination, and mutations. Influenza outbreaks are a prime example of this. The ability of diverse virus strains and mosquito species to infect, spread, and transmit viruses is known as vector competence.15 Aedes albopictus can now spread the chikungunya virus within a few days of ingesting infected blood, suggesting it is a more potent vector.14 Such attributes increase the challenge of dealing with epidemics or pandemics caused by rapidly evolving pathogens and their simultaneously adapting vectors.
• Increased Human-Animal Interaction: Growing human-animal interactions put human lives at constant risk by opening doors for the spread of new contagious diseases. Animals are forced to seek food in nearby human homes due to declining biodiversity, increasing conflict and interaction between humans and animals. To accommodate the need for meat, emerging nations have also begun to engage in intensive animal agriculture, mostly raising chickens and turkeys under lengthy shadows. Typically, between 15,000 and 50,000 birds are raised in this manner. The unnatural confinement of several animals indoors in a small area with restricted air flow and the generation of copious amounts of waste likely facilitate the quick selection, amplification, and spread of zoonotic infections.16
• Antimicrobial Resistance (AMR): Antimicrobial resistance in animal husbandry is mainly caused by antimicrobial usage. When a microbe no longer reacts to a medication to which it was previously sensitive, AMR emerges. Animal feed also contains antibiotics. Approximately 3% of the antimicrobials used in food animals worldwide are consumed by animals in India.17 
• Widespread International travel: Globally, the number of people travelling abroad has grown dramatically, accelerating the spread of infectious diseases, including zoonotic diseases, from one continent to another.

Therefore, developing and nurturing an efficient epidemiology surveillance network and exhaustive national territorial meshing is needed to capture animal diseases, including zoonotic and emerging diseases. Understanding the evolving epidemiology with respect to agent, host and environment through focused research and availing a database for the same is required. Ultimately, the need of the hour is employing a multidisciplinary, intersectoral one-health approach to reduce this ever-increasing trend of zoonotic diseases.

CONFLICTS OF INTEREST STATEMENT 

The authors declare no conflict of interest. 

 

SOURCE OF FUNDING 

None 

 

AUTHOR’S CONTRIBUTION

SH: Writing the draft

YAB: Conceptualization; Review & Editing

MH: Review & Editing

PA: Supervision; Review & Editing

REFERENCES

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13. Forest Survey of India. India State of Forest Report 2019. Ministry of Environment Forest and Climate Change. 2019. Accessed June 28, 2024. www.fsi.nic.in 

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