Unfortunately, the more you learn about these micro-organisms, the less at ease you will feel. It’s comforting though to remember that in human v virus warfare, our bodies’ defence strategies are in the main as sophisticated as the viruses’ attacks. The fact that the human race is still around at all means that as a race we have always been able to withstand extinction despite any viral attack. Of course, very many individuals have unfortunately lost the battle along the way ...
So: some terminology and explanation:
Firstly, a virus is not a bacteria. Repeat: IT’S NOT A BACTERIA! Even, pedantically, it's not a bacterium, which is what you have when a single bacterium gets separated from his bacteria.
This is probably the most prevalent confusion there is, the idea that all small disease-causing micro-organisms are generic "germs" and somewhat similar. Viruses and bacteria are NOT similar, and although both can cause illnesses ranging from the very serious to the hardly-notice-it type, they have completely different ways of operating ...
Viral illnesses include: Influenza, the Common cold, Rabies, Chicken pox, Measles, Aids, Hepatitis A, B, C, D, E, Polio, Herpes, and Smallpox. Meanwhile, there are some syndromes or illnesses which can be caused by both viruses and bacteria, such as diarrhoea, pneumonia, tonsillitis and meningitis.
Secondly, viruses are tiny. A virus in a cell is like a pea in a pillow... only smaller. OK, so all micro-organisms are small by human standards - but on average, viruses are far smaller even than bacteria.
This means that unlike bacteria, they can often only be seen with an electron microscope, and perhaps more worryingly, they can easily, for example, pass through the material of a surgical mask. It also means that if scientists don’t know what they’re looking for when there’s an outbreak of an unidentified disease, it can take a long time to find it, let alone learn how to combat it...
You can think of a bacterium as being an independently viable unit. Like a family in a dormobile. They may need to take food and water on board, but they’re basically fine by themselves, living on the road. Viruses by comparison are hitchhikers. They cannot survive long on their own, and certainly can’t thrive and replicate. They need the living cells of a ’host’ to do their business, and they are extremely good at doing this. Once in a host’s body, they can take advantage of the body’s own cells to manufacture vast quantities of new virus particles - enough to swamp the body’s defences, at least temporarily.
Considering how virulent an attack of the flu can be, it’s interesting to compare that while a human is thought to possess somewhere between 28,000 and 120,000 genes, a flu virus contains only TEN genes. (Some plant viruses can go so far as to have only ONE gene.)
Is a virus ’life’ as we know it? That’s a much-debated theoretical question. The tricky answer is that it depends on your definition of ’life’. Most scientists consider that life must have certain characteristics, eg. be able to reproduce, grow and develop, show variations based on heredity and be responsive. But when it comes to viruses, many of these criteria can be argued over, so viruses represent a real grey area. This is either confounding OR great for a pub discussion if you’re feeling argumentative. NB if you get bored discussing biological viruses, try the same discussion about computer viruses. Clearly they’re not life... or could they be??
Look around you - any plants, insects, animals or even other members of your family ... are all full of viruses. It’s thought that they have co-evolved with other life forms since the beginning of time - and they are present in the genome of even a new born baby.
If you’re writhing at the thought of your own body being full of viruses, it’s important to remember, many viruses are not harmful to their host. Because the virus and host have been together for millennia, they have developed a stable relationship together. That’s not to say they’re actually good for the host. The most useful virus we have come across is one that makes patterns on tulips. But they’re not actually "helpful" to the flower - just the florist!
The trouble often comes when the viruses ’jump species’. It’s estimated that 25% of viruses which affect animal populations - including humans - have originated from other animal species. These are viruses that were stable where they were, but when they reach a new species, they cause disease. These are known as ’emergent’ viruses. Why viruses can become so virulent when they infect a new species isn’t known, but devastating examples from the last couple of decades include HIV, which originated in chimps; Hantavirus, which originated in mice; Ebola, the origin of which is still unknown and Influenza which originates in birds.
To be ’emergent’ a virus has to cause an epidemic. This is defined as an outbreak that affects a whole community, not just individuals. If this happens on a global scale, it’s upscaled to a ’pandemic’..
That’s what some people say...
We humans have created conditions which make it far more easy for viruses to get out and about. We’ve hacked into new environments such as rainforests and disturbed the wildlife - and virus populations. People can get literally halfway round the world in 24 hours thanks to air travel - and consequently so can any virus they’re carrying.
And because our cities are now huge overcrowded masses of people, it’s very easy for an infection to be transmitted abundantly even before the carrier may realise they’re ill...