How Do Viruses Reach Humans From Animals?

Table of Contents (click to expand)

Viruses, after mutating, develop the ability to infect two different species. Thus, a virus that infects a type of animal can now infect humans as well.

From microbes to the air around us, there is an entire world of things that humans cannot see. However, in some cases, this can be a great thing! How would you be able to enjoy your fresh fruit and muesli in yogurt if you could see the yogurt bacteria crawling all over your bowl? However, there is one type of fascinating organism that has perpetually confused and surprised humans in terms of its existence and function—a virus!

Diagram showing different kinds of viruses(GraphicsRF)s
Most common disease-causing viruses (Photo Credit : GraphicsRF/Shutterstock)

Viruses are the category of microbes that are not living, as they only begin to live once they’re inside the body of a host. Viruses are one of those parasites that infect a variety of species on this planet. They are capable of infecting humans, animals, plants, and even bacteria! Viruses cause some of the deadliest diseases and have also been the causative agents behind several epidemics. The question is… how do they move from animals to humans?!

Recommended Video for you:

If you wish to buy/license this video, please write to us at

What Are Viruses?

Viruses are parasitic organisms, namely those that derives their nutrition from a host while simultaneously doing significant damage. However, the most fascinating thing about viruses is that they are non-living when they’re outside the body of the host, and are only considered “alive” once they’re inside. This may be why studying viruses and decoding their course of action in causing a disorder has always been difficult for researchers.

Blue virus cells or bacteria on white background(SkyPics Studio)s
The structure of a virus (Photo Credit : SkyPics Studio/Shutterstock)

A typical virus contains genetic material that can either be composed of RNA or DNA. Sometimes a protein coat is also present surrounding the genetic material. The genetic material is the main element in causing disease. In humans, the DNA codes for proteins that ensure the healthy functioning of the human body. Once the virus enters its host, whether it is a human or an animal, it takes over the normal cell machinery to create its own type of infected cells, rather than the healthy cells that would otherwise be created. The DNA in these infected cells has come from the viral blueprint and is not made of normal human DNA.

The process can be understood with the following example. Imagine a ship carrying lots of goods to a port on an eastern coast. Now, during its journey, it gets attacked by a group of pirates. The pirates take over the direction of the ship and navigate to the western coast, where they can easily trade the goods for a large sum of money. Similarly, after a virus replicates its genetic material and produces lots of infected cells, it will overcome the attack of the immune system from the cells in the host and cause the disease.

Also Read: Do Viruses Do Anything Outside Of The Body?

What Are Mutations?

The course of action outlined above is almost universal for viral infections. However, as time goes by, viruses develop mutations, which increases their potential to infect more than one species. Remember, viruses can typically infect either a human or an animal, but after its genetic material is mutated, it may develop the ability to affect both human and animals.

A mutation is a change in the sequence of DNA that may occur as a result of improper replication or some other external factors, such as exposure to the ultraviolet radiation of sunlight. Mutations can also be inherited, and such types can cause diseases like sickle cell anemia and phenylketonuria. However, mutations are not always harmful. According to evolutionary science, mutations are the phenomena that gave rise to the wide variety of species and the diverse world that we see today.

DNA helix break or Replace for concept of Genetic engineering(Anusorn Nakdee)s
The pink segment represents a mutation (Photo Credit : Anusorn Nakdee/Shutterstock)

Viruses also develop mutations in similar ways. A virus that affects a pig might get a mutation that allows it to cause sickness in humans. However, it won’t be able to do this unless a number of mutations accumulate. Once the mutation becomes powerful enough to cause a disease, it will then be able to infect both pig and human cells. This is precisely how the swine flu virus, better known as the H1N1 virus, evolved to cause an illness that could be transferred from pigs to humans.

Also Read: How Do Viruses Mutate?

How Do These Viruses Reach Humans From Animals?

The simple answer to this question is through physical contact. The first case of swine flu in North America was reported in those individuals who were taking care of infected pigs in a barn. Recently, there was also a Nipah virus outbreak in some southern Asian countries. It was found that in these regions, individuals were infected by the virus through direct contact with infected pigs and their contaminated tissues.

In the summer in the largest agricultural area of the south of Russia, quarantine was declared(galitsin)s
Infected Pigs (Photo Credit : galitsin/Shutterstock)

Once the mutated virus comes into contact with humans, it enters the body. Here, the cells of the immune system try to attack the viral cell and suppress the infection, but now that the virus has developed a mutation, it overcomes the immune response by attaching itself to these cells with the help of proteins coded by the mutated DNA. Thus, the mutated DNA helps the virus take over the host’s machinery to suppress the immune response, multiply inside the host, and finally cause the disease to spread!

Also Read: How Do Scientists Find “Patient Zero” Of A Viral Pandemic?


Viruses are also known as the intermediates between the living and the dead, namely due to their ability to live only once they are inside the body of the host. However, an important point to note is that mutations take a lot of time to accumulate. The process is slow and doesn’t take place every day, but due to a variety of factors, such as habitat loss and contaminated food, several viral DNA strains are mutating like never before. As it turns out, the world has a lot more to worry about than just climate change!

How well do you understand the article above!

Can you answer a few questions based on the article you just read?

References (click to expand)
  1. Introduction to the Viruses. The University of California Museum of Paleontology
  2. Virus replication | British Society for Immunology. The British Society for Immunology
  3. Viruses: Structure, Function, and Uses - Molecular Cell Biology - NCBI Bookshelf -
  4. TED-Ed (2019). How do viruses jump from animals to humans? - Ben Longdon. Youtube
Share This Article

Suggested Reading

Was this article helpful?
Help us make this article better
Scientific discovery can be unexpected and full of chance surprises. Take your own here and learn something new and perhaps surprising!

Follow ScienceABC on Social Media:

About the Author

Bhoomika has a degree in Biological Sciences from Sophia Girls College, Ajmer. Apart from writing, she adores travelling to offbeat destinations that offer more than just tourism. Being a strong supporter of women in STEM, she derives her inspiration from trailblazing personalities such as Marie Curie and Jane Goodall.