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What is a virus and how does it work?
We've all become more familiar with scientific terms, but do you really know your viruses from your bacteria?
Viruses drift on air currents, float in liquids and lie on surfaces. They enter when the host is eating or breathing.
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What is a virus?
A virus is a tiny infectious particle. It can be made up of a single or double string of genetic material, which is encased in a coat of protein. Viruses can be up to 500-times smaller than bacteria. While bacteria can be seen with simple light-based microscopes, viruses cannot. This made viruses invisible to scientists until the development of powerful electron-microscopes in the 20th century. Because of this, viruses were only identified for the first time about 100 years ago.
Unlike bacteria, viruses can only survive in living cells. Viruses trick or force the host cell to replicate itself. Bacteria are susceptible to antibiotics, viruses are not.
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How does a virus invade a living cell?
On the surface of every living cell there are a series of receptors which act like locks in doors. These locks can only be opened by a virus that has the right key to unlock the cell door. Having this key is a result of evolution – the virus with a key that fits, is the disease that infects the host’s cell. Once the door is unlocked, a string of genetic material enters the host’s cell and tricks it into making copies that then infect other cells. Coronaviruses use their spikes to stick to the lining of body cavities. This is particularly the case in the respiratory system. The virus attaches to the lining of the air passages and many patients with Covid-19 can develop severe respiratory distress.
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How do we defend ourselves?
Our outer layer of skin is tough. We have mucus and tears and stomach acids to destroy viral invaders. Tiny hairs in our noses and throat help to trap and expel invaders, including viruses. When these fail, we have specialised cells, antibodies and T Cells which gobble these aliens up. The antibodies and T cells roam along our arteries and veins to discover and destroy cells already infected. They also share and store memories of previous invaders so that the next time a virus enters your body, they will quickly recognise and destroy it. This is your immune system giving you immunity to infectious disease.
When does a virus cause an epidemic or a pandemic?
An epidemic is an infectious disease that is widespread in a community at a particular time. A pandemic is an epidemic occurring worldwide, or over a very wide area, crossing international boundaries and usually affecting many people. The biggest infectious disease threat to human existence are viruses. Epidemics of influenza, measles, chickenpox, mumps, German measles, HIV, and Ebola have all been caused by viruses.