By Shafia London
We have all had colds or the flu with symptoms of fever, congestion, coughing, sore throat. Colds and flu (influenza) are caused by viruses. Viruses are responsible for many other serious, often deadly, diseases including AIDS, Ebola haemorrhagic fever, infectious hepatitis, and herpes. In this edition, we look at how can viruses cause so much trouble? What makes us so vulnerable to them?
We live in a sea of organisms. Bacteria, viruses, parasites, and other life forms great and small are everywhere. Animals and plants are full of them! Most cause no harm in the bodies in which they have evolved — even humans. Ebola does not cause disease in bats. Neither does coronavirus. Some of the viruses that have caused great harm to humans in recent decades —including this new coronavirus and its predecessors, SARS and MERS — have jumped from animals to humans. That was also true for the virus that causes AIDS. As human behaviour changes, whether it’s our dietary habits or growth of cities that push us into contact with things we weren’t previously in contact with, we get exposed to new viruses. They cause disease in our bodies because they are new to us — they’re exploiting a new habitat.
For example, a little boy goes outside and plays near a tree where bats roost, he might pick up a piece of fruit that has some bat poop or bat saliva on it and put that in their mouth, and then an opportunity has been created for the virus that live in the bat’s body to enter into a human body. We know that with Ebola, there was a single spill over event — the first case was a 2-year-old child in West Africa who was playing near a tree where bats live.
Viruses can get into the body through the mouth, nose, breaks in the skin, eyes and genitals (privates). Once inside, they find a host cell to infect they can stop body parts from working properly or attack and damage a part of the body. For example, cold and flu viruses will attack cells that line the respiratory or digestive tracts. The human immunodeficiency virus (HIV), which causes AIDS, attacks the T-cells of the immune system.
Regardless of the type of host cell, all viruses follow the same basic steps in what is known as the lytic cycle. It gets in and hijacks the human cell’s machinery. Instead of the cell doing what it is supposed to do, the virus turns it into a machine to make more of the virus. It goes and goes and goes until the immune system stops it. Viruses act as blueprints or a code to turn cells into machines to make more virus.
The new viruses break free from the host cell by destroying the host cell or break away (budding) with a piece of the cell membrane surrounding them. Once free from the host cell, the new viruses can attack other cells. Because one virus can reproduce thousands of new viruses, viral infections can spread quickly throughout the body.
The sequence of events that occurs when you come down with the flu or a cold is a good demonstration of how a virus works:
- An infected person sneezes near you.
- You inhale the virus particle, and it attaches to cells lining the sinuses in your nose.
- The virus attacks the cells lining the sinuses and rapidly reproduces new viruses.
- The host cells break, and new viruses spread into your bloodstream and also into your lungs. Because you have lost cells lining your sinuses, fluid can flow into your nasal passages and give you a runny nose.
- Viruses in the fluid that drips down your throat attack the cells lining your throat and give you a sore throat.
- Viruses in your bloodstream can attack muscle cells and cause you to have muscle aches.
Your immune system responds to the infection, and in the process of fighting, your body temperature increases. This fever helps you to fight the infection by slowing down the rate of viral reproduction, because most of your body’s chemical reactions have an optimal temperature of 98.6 degrees Fahrenheit (37 degrees Celsius). If your temperature rises slightly above this, the reactions slow down. This is why a temperature check is a good indicator of a viral attack. This immune response continues until the viruses are eliminated from your body. However, if you sneeze, you can spread thousands of new viruses into the environment to await another host.
Then the virus starts to spread. Next time, we look at how viruses spread!
Shafia London holds a BSc (1st Hons) Major Biochemistry and Double Minors in Communication and Human Resource Management from the University of the West Indies. She is a MSc Biochemical Engineering Graduate of the world-renowned University College London. Before returning to the Caribbean, she worked briefly as a researcher with University College London studying the use of Pichia pastoris in commercial vaccine production through recombinant DNA techniques. She then switched to business and is now completing and MBA and is the Commercial Manager, Banks Holdings Ltd group of companies — manufacturers of Banks beer, Deputy Beer, Plus, PineHill Dairy juices and Milks among other popular products