- By Dr Sagarika Borah
Today is 6th July and is observed as “World Zoonoses Day”. The significance of this day is that it reminds us of the persistent threat of zoonotic diseases and the importance of coordinated efforts to prevent their transmission.
Most of the infectious diseases affecting humans are of animal origin. Any disease or infection that is naturally transmissible from animals to humans is referred to as Zoonotic disease. The World Health Organization (WHO) estimates that 61 percent of all human diseases are zoonotic in origin, while 75 percent of new diseases discovered in the last decade are zoonotic. Zoonosis is a great public health concern and a direct human health hazard that may even lead to death. Across the globe, the zoonotic diseases have caused an estimated 2.4 billion cases of illness and 2.7 million deaths in humans per year in addition to their negative effect on human health. Zoonotic outbreaks can also severely impact livestock production, trade and livelihoods. Recent outbreak of COVID-19 is the classical example of zoonotic disease which is caused by the virus SARS-COV2 and is believed to have started in Huanan Seafood Wholesale Market in Wuhan, China.
Every year, “World Zoonoses day” is observed on 6th July to commemorate the historic achievement of Louis Pasteur, who administered the first successful rabies vaccine on 6 July 1885. This day was first formally observed on July 6, 2007, to honour the 100th anniversary of Louis Pasteur’s death and to spotlight the continuing global threat of zoonotic illnesses. It helps to raise public awareness and to educate people on disease transmission pathways and preventive measures. Observance of World Zoonoses Day also supports scientific innovation in surveillance, diagnosis and vaccine development.
People can get zoonotic diseases directly or indirectly from animals like infected domestic animals, poultry, rodents, reptiles, amphibians, insects, and other wild animals. Diseases that are transmitted directly to humans from animals through media such as air are known as direct zoonoses. Avian influenza is one of the examples of direct zoonoses which is a viral disease that spreads from animals to humans through droplets or fomites. Infected animals can also directly transfer pathogens to susceptible humans by bites such as in the case of rabies, which is one of the deadliest zoonotic diseases. Arthropods like mosquitoes and ticks are often considered to be the only vectors; however, any animal that has the potential to transmit pathogens to humans can be considered a vector. Many zoonotic diseases have the potential to cover long distances and affect the world.
Domestic animals play a significant role in the transmission of various zoonotic diseases to humans and in many cases, they work as amplifiers of pathogens emerging from wild animals. Cattle, sheep, goats, dogs, cats, horses, pigs, and other domestic animals act as reservoirs of pathogens of domestic zoonoses and can transmit the diseases to humans. Pathogens can be transmitted through direct contact or animal origin foods. Examples of common zoonotic diseases that can be transmitted to humans from domestic animals include anthrax, rabies, tuberculosis, brucellosis, campylobacteriosis, leptospirosis, toxoplasmosis, , toxocariasis, listeriosis, rotavirus infection, Q fever etc.
Rabies may be the oldest zoonotic disease known to man and is most readily transmitted by the bite of an infected mammal. Domestic dogs are the main source of rabies deaths in humans contributing up to 99% of cases. Once clinical symptoms appear, rabies is certainly 100% fatal. Rabies is an important threat to public health. More than 55,000 people die of rabies every year in Asia and Africa and as many as 20,000 people die annually in India alone.
Tuberculosis is the most common zoonotic disease that comes from cattle to humans having serious public health significance. The disease has been significantly a cause for severe economic loss in animal production. Most humans are affected with tuberculosis through contaminated milk or via aerosols from coughing of infected animals. Though bovine tuberculosis has been greatly eliminated from developed countries, other parts of the globe are still facing serious zoonotic effects. Human tuberculosis is the second most common cause of death after AIDS.
Brucellosis is another common bacterial zoonotic disease causing over 500,000 human cases throughout the world every year. The disease is classified as a forgotten neglected zoonosis as per the WHO. It comes to humans through the consumption of unpasteurized milk or milk products. In humans, brucellosis mainly causes influenza-like infections, pneumonia and other complications including meningitis, endocarditis, septicemia, serious weakness, pain in muscle and joints, extreme headache, fever, and night sweats. Anthrax is also a deadly zoonotic disease which poses a significant public health importance. Japanese encephalitis is another common zoonotic disease caused by the Japanese encephalitis virus and spread primarily by the Culex mosquito. The outbreak of Nipah virus in Kerala is also an example of zoonotic diseases. Nipah virus was discovered when it caused a serious outbreak of viral encephalitis among pig farmers in Malaysia in 1998. The list is long. The World Health Organization (WHO) reports that there are over 200 known types of zoonotic diseases leaving the human population at high risk. These diseases can affect anyone, but farmers, livestock keepers, veterinarians, butchers and pet owners are at greater risk because of their close contact with animals.
Nowadays, people are more affectionate to companions and pet animals. This also puts human health at risk due to the possible spread of infections. In many houses now, pets of exotic species are kept along with common pets. Therefore, huge numbers of people are at risk of acquiring new zoonotic diseases from pets, companion animals and exotic birds and animals.
Food acts as an important medium to transmit pathogens causing diarrheal diseases. Many food-borne illnesses are caused by zoonotic pathogens. It is estimated that about 600 million (1in10 persons around the world) people annually consume contaminated food and water. Risk factors influencing food-borne zoonoses include handling and slaughtering of animals without appropriate precautions and consuming undercooked animal-based food.
In this context, there is an urgent need for an integrated strategy to prevent and control zoonotic diseases. For this, “One Health Approach” concept was adopted to properly deal with global health challenges. The one health concept encourages collaborations among wildlife biologists, veterinarians, physicians, agriculturists, ecologists, epidemiologists, and biomedical engineers to ensure favorable health for animals, humans and our environment. Since some zoonoses can spread swiftly across the globe to affect global communities, coordinated surveillance approaches at local, regional, national, and international levels are essential to control zoonoses.
India has taken several important steps to prevent and control zoonotic diseases. The government is promoting the National One Health Mission, which encourages collaboration between doctors, veterinarians, and environmental experts. The Integrated Disease Surveillance Programme helps in early detection and monitoring of outbreaks. The National Animal Disease Control Programme works to control major livestock diseases. Mass dog vaccination campaigns, food safety regulations and public awareness programmes are also being strengthened. Research institutions and veterinary universities continue to work on disease diagnosis, prevention and farmer education.
Zoonotic diseases are not new, but their frequency and spread have increased due to changing lifestyles, urbanization, deforestation, climate change and increasing movement of people and animals. The recent COVID-19 pandemic reminded the world how a disease can disrupt lives, economies and healthcare systems globally. Strengthening surveillance, improving public awareness, promoting vaccination and enhancing collaboration between veterinary and medical sectors along with environmental experts are key to preventing future outbreaks. By working together, we can reduce zoonotic risks and build a healthier, safer world for both humans and animals.
(The writer works at the ICAR-Krishi Vigyan Kendra, West Garo Hills, Meghalaya)
