Zoonosis: Diseases of Animal Origin

Protection of Forests, Biodiversity and Creation Robust Veterinary Infrastructure is the Need of the Hour for the Survival of Mankind

Zoonosis: Diseases of Animal Origin
Zoonosis: Diseases of Animal Origin

 Instances of so many disease outbreaks, like Ebola, Severe Acute Respiratory Syndrome (SARS), Bird Flu, Swine Flu etc. over the past few years including the present COVID-19 outbreak has reignited  the curiosity, of not only the scientific community but also the common people,  about a special class of diseases known as Zoonotic diseases.

A zoonotic disease or zoonosis refers to “any disease or infection that is naturally transmissible from vertebrate animals to humans”.


Disease or infection that is naturally transmissible from vertebrate animals to humans is called zoonosis. Zoonotic disease may be viral, bacterial or any other unconventional agents. The COVID-19 pandemic has shown the world the drastic impacts of zoonotic diseases. In recent years zoonotic diseases have increased for example swine flu, avian flu, nipah virus infection and the most recent COVID-19.

This is however not a new class of diseases. As a matter of fact, there had been disease outbreaks of such kind before in human history, as for example, the West Nile Virus (a disease said to have been transmitted to humans from birds),  outbreak in North America in 1999, Bubonic Plague (believed to have been transmitted from rodents) which had been the cause of the infamous “Black Death” pandemic in Europe and Asia during the 14th century.

The term Zoonosis was coined by a German physician, Rudolf Virchow in the mid 1800s.

According to United Nations Environmental Program (UNEP) nearly 60% of all previously known infectious diseases and nearly 75 % of all new and emerging forms of infectious diseases in humans are zoonotic in nature.

Transmission of Zoonotic Diseases Info 2
Transmission of Zoonotic Diseases

Transmission of Zoonotic Diseases

Zoonotic diseases can spread from animals to humans through various ways. Some of them includes:

Direct Contact– It involves coming into contact with saliva or excreta of infected animals.

Indirect Contact- It involves coming into contact with the areas where the infected animals live, like aquariums, chicken coops, pet habitats etc.

Vector Borne- It involves the transmission of disease by vectors, which are living organisms that can transmit infectious diseases between humans or from humans to animals. Most common form of the vectors include mosquitoes, fleas etc.

Water Borne- It involves coming into contact with water that has been contaminated with the excreta of infected animals.

Some Well Known Global Zoonotic Outbreaks of the 21st Century and Their Casualties 

Some well-known global zoonosis outbreaks of the 21st century include:


Believed to have been transmitted from Civet cats, the outbreak of SARS (Severe Acute Respiratory Syndrome) in the year 2002 had resulted in more than 700 deaths across 29 countries worldwide and an estimated economic casualty of around $41.5 billion. The pathogen that had caused the disease is known by the name of SARS coronavirus (SARS-CoV).

Avian Influenza Outbreak of 2004

Believed to have been transmitted from the poultry farms of Vietnam and Thailand, the Avian influenza outbreak in Asia in the year 2004, have caused deaths of more than 100 people between 2004 and 2006, according to World Health Organization (WHO) . It has also resulted in economic loss of around $ 20 billion. It was caused by a strain of virus known as H5N1.

Ebola Virus Disease (EVD) Outbreak of 2014

The EVD disease outbreak in the year 2014 in Africa was declared by WHO as ” Public Health Emergency of International Concern”.  The disease was believed to have been transmitted to human population from body fluids and excreta of infected animals like fruit bats gorillas etc. mainly found in the African rain forests, possibly due to humans coming in close contact with these animals on account of forest loss.


The present Coronavirus disease outbreak, which started in Wuhan, China is as yet one of the worst biological hazards that the world has faced in the 21st century. Noting the fast spread of the virus across the world since December 2019, WHO declared the disease to be a pandemic in March 2020. Till now the disease has claimed more than 5 lakh human lives worldwide with USA and Brazil bearing the maximum brunt of the casualties. The disease is said to have been transmitted from the Seafood wholesale markets of Wuhan.

Zoonotic Diseases in India

India is considered to be one of the  ‘hotspots’ of Zoonotic diseases, as many of the diseases that frequently affects its populace are of animal origin and these diseases have been creating a huge burden to the country in terms of morbidity and mortality.

Some of the major zoonotic diseases that frequently affects the Indian population includes Rabies, Japanese Encephalitis, Nipah virus infection, Kyasanur Forest Disease (KFD) etc. among many others.

Primary Causes of increasing spread of Zoonosis Info 1
Primary Causes of increasing spread of Zoonosis

Primary Causes of increasing spread of Zoonosis

According to UNEP, some of the primary reasons that leads that leads to the transmission of animal diseases into human population includes:

Livestock Farming and Animal Husbandry

Domesticated animals serve as a ‘bridge’ for the pathogens originating in the animal populace to enter into human populace, what makes matter worse is the large scale use of antibiotics, in the livestock industry, for the purpose of maintaining the health of animals and the productivity of livestock products. This has led to many pathogens developing immunity to most first-line drugs (those drugs that are “first prescribed against a disease, due to their less side effects and high clinical efficacy”). This condition is known as Antibiotic Resistance.

Environmental Changes

Changes for example in patterns of weather, extreme weather events, can modify the areas of distribution of the disease-causing pathogens and the vectors of the disease. As one of the primary causes of climate change, the global warming is also responsible for pushing the infected host animals into new territories thereby spreading diseases into new areas.

Ecological Disturbances

Ecological disturbances resulting in particular from human activities like deforestation, migration, agricultural intensification, encroachment into forests etc. creates change in the behavioral pattern of the pathogens and hosts (both human and animal). An effect of this is the increasing proximity of the human and wildlife populace and providing gateway to the zoonotic pathogens to exploit multiple hosts.

Steps Taken by the International Organizations and The Government of India to Control Spread of Zoonotic Diseases

Several initiatives have been taken at the global level, by various International Organizations and also by the government of India in response to the increasing threat of spread of zoonosis. Let us discuss some of them.

Some of the major initiatives at the international level include:

Promotion of “One Health”

 The conception of “One Health” as defined by the One Heath initiative Task Force (OHITF) refers to “the collaborative efforts of multiple disciplines working, locally, nationally and globally, to attain optimal health for people, animals and our environment”.

The framework for the implementation of the conception of “One Health” was developed by a joint collaboration of the Food and Agricultural Organization (FAO) , World Health Organization (WHO),  World Organization for Animal Health (OIE), UNICEF, United Nations System Influenza Coordination and World bank, in the year 2008.

Some of the chief International organizations who are at the forefront in the promotion of the conception of “one health” includes: WHO, OIE, FAO, CDC (Centers for Disease Control and Prevention) among others.

Animal Disease Detectives Programme

In the wake of the COVID-19 crisis a 3-year training program to create a unique team of individuals known as “animal disease detectives” has been established under the patronage of The Australian Department of Foreign Affairs and Trade. The objective of this team is to “engage with the government animal health authorities and educators in the Asia-Pacific region  for strengthening the capacity to detect, respond, control and prevent animal disease outbreaks “.This will mainly be based in South-East Asia and Pacific. For the training of the members of this team a consortium of veterinary scientists has been created.

As far as India is concerned, the central government has its own set of initiatives launched via the National Centre for Disease Control (NCDC). This includes: The Integrated Disease Surveillance Programme (IDSP) (which is a World Bank Supported Program under the ministry of Health and Family Welfare), National Programme on Containment of Antimicrobial Resistance  (which was launched as a part of 12th five year plan), National Viral Hepatitis  Surveillance Programme etc. among many others.

Recently, the Government of India also launched the National Animal Disease Control Programme , which is a 100 % central government funded programme, whose objective is to vaccinate 500 Million livestock and 36 Million Female Bovine Calves with the twin aims to control the spread of Foot and Mouth Disease (FMD) and Brucellosis by 2025 and full eradication of these two diseases by 2030.

The central also has plans to make veterinary public health a part of its National Health Mission and to conduct research studies on the economic impact of zoonotic disease outbreaks, which will in turn help the medical and veterinary communities to prepare guidelines for the prevention and control of these diseases, well in advance before any future outbreaks.

Challenges in Controlling Zoonotic Diseases in India 

Considering the unique socio-economic scenario of India, it is quite understandable that controlling any form of disease outbreaks and in particular outbreaks of zoonosis is a formidable task.

Firstly, the huge population of India on the one hand and the unchecked unsustainable human activities on the other hand make it an extremely challenging task to prevent human and animal interactions.

Secondly a large section of Indian populace is poor and many of these poor people are dependent on rearing animals for their livelihood. This brings them in close contact with animals and poses the risk of catching zoonotic infections.

Also lack of robust vaccination programmes, poor surveillance infrastructure combined with lack of mass awareness about these diseases and lack of proper diagnostic infrastructure facilities make it extremely difficult to prevent and control the spread of diseases.

Conclusion and Way Forward

The Biodiversity of the forests serve as a ‘containment bottle’ for the zoonotic pathogens, where they coexist ‘harmlessly’ with the animal and plant populace. It is therefore in the interest of the survival of mankind to make all possible efforts to conserve these forests and prevent any form of unsustainable activities there.

Also, Environmental Impact Assessments should be done on a frequent basis for different construction projects along with this environmental clearance procedures for different developmental projects should be made more stringent.

The government should also make efforts to plug the loopholes in the implementation processes of the existing vaccination programmes, implement robust surveillance mechanism so as to detect the  diseases and infections at the source level (i.e. the animals) itself so as to prevent ‘spillover’ of the pathogens into human community. Also, more and more veterinary institutions must be created and for that the Public-Private-Partnership gateway may be employed. The decision of the government to make veterinary public health a part of its National Health Mission is therefore a right step in this regard.

Large scale mass awareness programmes are also very important to educate the people regarding these diseases and their prevention. Various e-governance initiatives and media can play a vital role in this regard.


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