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Zoonotic diseases, or zoonosis (zoonoses in plural), are infections or diseases that are passed on from animals to human beings. 

Severe acute respiratory syndrome coronavirus 2 or SARS-CoV-2, the virus responsible for the 2019-20 COVID-19 outbreak, is only the latest such pathogen to cause havoc worldwide.

HIV/AIDS is an example of a zoonotic disease, as it crossed over from primates to humans in the 1920s in what is now the Democratic Republic of the Congo.

Swine flu is another example. It started out as a type of bird flu that couldn't affect humans, till it mutated inside a pig (swine) to become a pathogen that can indeed harm people—swine flu caused an outbreak that started in America in 2009 and spread as far as India. 

According to a study published in the journal Philosophical Transactions of the Royal Society, as many as 1,415 different pathogens cause diseases in humans. Of these, 868 or a staggering 61%, are zoonotic.

It is also estimated that of an additional 175 pathogens responsible for emerging diseases today, 132 may be zoonotic.

Zoonotic diseases can be of varying types, from routine infections that can go away in a matter of days to severe and life-threatening ones, much like the new one that has resulted in a global pandemic that has lasted over seven months. So far, more than 12 million people have been infected by COVID-19 and the death toll has crossed 555,000 the world over.

Read more: World’s deadliest viral infection

COVID-19 is a zoonotic disease

COVID-19 is suspected to have spread from the wet market (an animal, seafood and wild meat market) of Wuhan in China. Ever since then, there has been growing concern about diseases that can be passed on from animals—either by eating their meat or by being in close contact with them—in the future.

The SARS-CoV-2 virus, which causes COVID-19, is one of seven known coronaviruses that infect humans. Historically, these viruses have been passed on from bats to either humans or to other animals that act as carriers as well.

A carrier, also known as a vector, is a living being that carries the disease but doesn't get sick—mosquitos and ticks are prime examples of vectors.

Earlier coronaviruses were responsible for the outbreaks of Severe acute respiratory syndrome SARS in 2002 and Middle East respiratory syndrome or MERS in 2013.

  1. Types of zoonotic diseases
  2. How zoonotic diseases spread
  3. Symptoms and diagnosis of zoonotic diseases
  4. Prevention of zoonotic diseases

Types of zoonotic diseases

Zoonoses are caused by different kinds of pathogens that can cause:

Some of the common carriers of such pathogens are mosquitos, which are known to spread infections such as malaria, dengue fever and chikungunya.

There are several zoonotic diseases that have frequent outbreaks, as well as others that are rarer by comparison. However, such zoonotic diseases have made their presence felt all throughout human history. Some of the common zoonotic diseases are:

How zoonotic diseases spread

There are a few different ways that zoonoses infect and spread into a human population:

  • Insect bites from mosquitos or ticks
  • Eating contaminated meat or produce from infected animals
  • Aerosol transmission, or through the air
  • Through close contact with animals, such as in farms or poultry farms
  • Touching an infected part of an animal, and catching the infection

The spread of diseases like swine flu and bird flu is said to have started through pig and poultry farms, where people came into contact with infected animals, who then passed the disease onto others through other modes of transmission.

Even families owning pets at home are at risk of contracting zoonotic disease through ticks and other insects.

Symptoms and diagnosis of zoonotic diseases

Zoonotic diseases are caused by different pathogens—many of the symptoms are specific to the kind of pathogen that has infected the human body. As mentioned earlier, some diseases are more dangerous than others, and due precaution must be practised either while handling animals in a farm, zoo or similar environments, or at home, if you have pets.

Initial symptoms of zoonotic diseases, especially those caused by insect bites, can range from rashes on the skin, fever, headaches or dizziness, while in respiratory infections such as COVID-19, signs of breathing difficulty, chest pain, cough, fever, diarrhoea and several others can be seen in patients who may have come in contact with the pathogen either through an animal or by breathing in contaminated air.

Any of the above-mentioned signs developing should warrant a visit to the doctor to get it thoroughly investigated. Doctors usually take blood samples and perform other tests to arrive at the right diagnosis, and advise the next course of action.

Larger animal bites such as from dogs must be attended to immediately to avoid diseases such as rabies. Doctors usually give anti-rabies injections in such cases, or vaccines should be taken in advance to prevent such zoonotic diseases in the future as well.

Some individuals, however, are more at risk of contracting zoonotic diseases, either due to a weakened immune system, age (such as young children, people older than 60 years of age), life stage such as pregnancy, or those suffering from pre-existing conditions such as cancer, diabetes or HIV/AIDS.

Prevention of zoonotic diseases

While emerging zoonotic diseases from unknown pathogens pose a serious risk to life for many people—COVID-19 has been a case in point—the risk posed by several zoonoses in the past have reduced due to the development of vaccines that can prevent such diseases from infecting an individual. Treatment options have also become available to cure patients of infections that may have claimed thousands of lives in the past.

Read more: Vaccine made out of mosquito spit out to stop next disease outbreak

The outbreak of mosquito-borne diseases such as malaria, dengue fever and chikungunya almost every year in various parts of India and other tropical regions means preventive measures must be followed to protect people and their families. The outbreak of other zoonoses caused by the practices of animal farming can also be avoided by enforcing the right safety regulations, which can prevent large numbers of people from getting infected.

Some daily practices that people can follow to prevent the onset of various zoonotic diseases are:

  • Practising proper hand hygiene by washing hands with soap and water, or cleaning them with alcohol-based hand sanitizers when soap and water are not available.
  • Using mosquito repellents in the form of ointments, sprays or patches in monsoon seasons. You could also use a mosquito net.
  • De-infecting homes with sprays and getting indoor spaces cleaned through periodic pest control measures
  • Buying fresh produce such as meats, animal products, fruits and vegetables, washing them properly before use and cooking them properly before consuming them. (Read more: How to wash fruits and vegetables during the COVID-19 pandemic)
  • Be up to date on your pets' vaccinations and take them to the vet for their regular checkups.
  • Look out for ticks in and around your house if you live with pets, and use the right sprays and pest control to keep your family safe.
  • Avoid animal bites and frequent contact with animals other than your pets.
  • Wear masks and gloves when working in an animal farm and handling sick animals, and avoid touching your face or any foods after handling them.
  • Report to a doctor immediately in case an animal bites or scratches you—clean the wound properly.
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