How Does Zoonosis Transfer From Animals To Humans? 
A critical reason for the spread of zoonotic diseases is rapid urbanization and the loss of natural habitats for wild animals.
World Health Organisation (WHO) defines zoonotic diseases as any infection transmitted from animals to humans (and vice versa). Among the human pathogens, approximately 61 per cent are zoonotic. Consequently, they are of significant public health concern worldwide, with some spreading across the globe, as seen in the ongoing covid-19 pandemic.
According to Dr Supradip Ghosh, Director and Head, Critical Care Medicine, Fortis-Escorts Hospital, Faridabad, potential sources of zoonotic pathogens can be both domestic and wild animals. However, approximately 71 per cent of emerging zoonoses are sourced from wild animals. Markets selling exotic meats are especially high-risk areas with a potential for spreading hitherto undocumented zoonoses. Also, people staying closer to the wilderness are at a higher risk of contracting zoonoses. One important reason for the spread of zoonotic diseases is rapid urbanization and the loss of natural habitats for wild animals leading to increasing contact between animals and humans. Agricultural workers are at a higher risk of getting zoonotic infections because of the apparent reason.
Zoonotic Diseases And Human Transmission
Zoonotic diseases can be transmitted to humans directly through media such as air, fomites, ingestion of food or through contact with body fluids (e.g. saliva, blood, urine, faeces). One classic example of the direct spread of zoonoses through the air is avian influenza, a viral disease that spreads through droplets of fomites.
- Infection can spread to humans through contact with non-intact skin like cutaneous anthrax. Interestingly, anthrax pneumonia, the more dangerous anthrax, is spread by inhalation of anthrax spores. Diseases like rabies, a universally fatal viral infection, spread through the saliva of an infected animal (e.g. dog, monkey, bat or racoon) when the animal bites humans.
- Some zoonotic diseases are spread by ingesting undercooked contaminated meat/egg or unpasteurized milk, including common bacterial infections like typhoid fever, parasitic infections like trichinellosis, or viral infections like a rotaviral disease.
- For example, the origin of the recent monkeypox epidemic is possibly related to the consumption of undercooked meat from infected animals like wild squirrels. Zoonotic diseases can also spread from infected humans to others, e.g. Ebola or monkeypox.
Can Zoonoses Spread Indirectly?
Zoonoses can also spread indirectly through vectors, e.g. mosquitos, ticks, or other vectors. Some examples of mosquito-borne zoonotic diseases include dengue, chikungunya, yellow fever, West Nile fever, Japanese encephalitis etc. In addition, several zoonotic infections are spread through tick-bite, e.g. rickettsial infection, babesiosis etc.
“An Ounce Of Prevention Is Worth A Pound Of Cure”
Simple measures like hand washing, safe drinking water consumption, or proper cooking can prevent many zoonotic diseases.
- Vaccinating pets against diseases like rabies is recommended. In addition, handling sick animals or animals with open wounds should be avoided unless with gloved hands.
- Animal shelters should be cleaned regularly, following standard guidelines. Sickness in animals, especially those kept in herds, e.g. poultry farms or barns, should be reported to appropriate authorities.
- It is essential to avoid getting bitten and scratched by animals. While in the wild, clothing gear must be relevant, and one should be alert around animal habitats.
- If bitten, the exposed area must be washed thoroughly with soap and running water. To avoid its spread, being informed and aware of zoonotic diseases is vital.
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