When we hear the term ‘virus’ we mostly associate them as a threat and think that they are harmful, but contradictory to this belief, viruses are not harmful and are not always detrimental to our health as they help in fighting various diseases, some viruses also help in fighting cancer. With this article, we dive deep into the world of viruses and their ecosystems called virome.
The human body is nothing less than an ecosystem, the human body on average plays host to approximately 40 Trillion bacterial cells and along with that we also have the Human microbiome (a community of microorganisms, such as bacteria, fungi, and viruses, that live in a specific environment). These bacteria have a symbiotic relationship with us, they help in breaking down meals and synthesising the various vitamins and minerals in our body, along with helping in neutralising acid in the mouth and aiding in balancing the immune system but most importantly these useful bacteria take up intracellular space preventing the harmful bacteria from taking over. Although these bacteria help us in various aspects of our lives, this relationship between the bacteria and our body is very fragile as all these bacteria just look out for themselves, multiplying and increasing their numbers. To keep these bacteria at bay and to maintain a balance in our body we need a predator that can hunt these excessive bacteria (both good and bad) and viruses take up the role of maintaining this balance.
On average there are over 380 trillion viruses in the human body, and different species of viruses exist. Over 1,40,000 viral species live in the human gut, around 18 million on our skin and at least 10 billion in a single drop of our saliva, recent studies also show that even the cerebrospinal fluid that was first thought to be completely sterile contains thousands of viruses hence it is important for us to understand the role of these viruses in our human microbiomes.
A bacteriophage is a virus that attacks and infects bacteria. The name comes from 2 Greek words i.e. phagein, meaning “to eat” and Bacteria. Bacteriophages are of two types:
1) Virulent bacteriophages: which follow something called the lytic cycle (they break down the host)
2) Temperate bacteriophages which can follow both the lytic and lysogenic cycle (they can utilise the nutrients extracted from the host without killing it).
The viruses that affect and hunt the harmful bacteria in our body are the virulent bacteriophages. To understand the functioning of virulent bacteriophages and lytic cycles further, let’s take the example of a virus known as Lambda Phage where Lambda phage attaches itself to the bacteria E.coli with its spider-like legs which helps grab the bacteria for attachment. E.coli is useful for synthesising various vitamins, but it also has a virulent variant that is harmful and causes diseases like diarrhoea, infections of the urinary tract, pneumonia, sepsis, and other illnesses. Once attached the Lambda Phage penetrates the E.coli bacterium and with its syringe-like bottom injects its DNA disabling the bacteria’s defences and controlling the bacteria till it is completely exhausted of all of its resources, nutrients and energy. After this, the phage makes the bacteria burst releasing thousands of new young viruses into the body. Another approach that the virus takes is that instead of killing the bacterium it integrates and combines its DNA into the bacteria’s genome and if the bacteria reproduces the virus DNA in the bacteria also replicates. Once this integrated bacteria multiplies sufficiently and has favourable conditions the viral DNA reactivates and like a ticking time bomb it releases its viral DNA in action.
The oncolytic virus is a virus under research to be used to treat cancer. In simpler terms, a virus that hunts down cancer cells is known as an oncolytic virus. Oncolytic viruses can specifically infect and damage cancer cells while ideally sparing and ignoring normal cells. There are some strains of Newcastle Disease Virus and Reoviruses these viruses usually ignore the healthy cells and attack the cancer-infected tumour cells while the cancer cells are good at fighting the immune system they are not good at fighting back these viruses. Oncolytic viruses target the specific adaptations of cancer cells attacking them at sites where their defences are the weakest. Since these cells are mutated it is easy for the viruses to take over the cancer cells and multiply using these cancer cells as a virus production factory. Once the host cell is exhausted of its resources it explodes releasing multiple new viruses that will replicate the same action thus starting a chain reaction. While all this is happening the virus also attracts the immune cells which start attacking the tumour. Another interesting fact is that these viruses destroy the microenvironment that cancer cells create and use against the human body to keep the immune system at bay, despite these facts the virus is still under research and as a part of the research they are working very well with chemotherapy or radiation therapy. Scientists are working and researching these viruses to utilise their oncolytic abilities and save the lives of countless people.
In Conclusion, Viruses are not just harmful or not completely beneficial to the human body but like everything in life, they are like two faces of the same coin. In this world where there exists a single universe with approximately 200 billion galaxies and numerous planets in our own galaxy, we still are unable to determine the nature of one of the smallest living organisms like viruses. Hence, teaching us to not judge a book by its cover.