What Motivates Germs to Infect Our Bodies?

[mktsgm]

I wonder what could be the motive for a bacteria or a virus to invade our body. If it finds food in us, what serves as food?

What would have happened to that particular germ, had it not infected someone?

 

[DrClaude]

There is no motive. Bacteria and virus evolve randomly, under natural selection pressures. Whatever allows a bacterium or a virus to replicate will stick.

There is also a limit to infection. If an infection is too strong and kills its host before it can replicate and infect someone else, it will go extinct.

 

[jim mcnamara]

Humans have large number of friendly bacteria on the skin and in the gut. So not all germs are bad. Dr Claude's explanation is right on. You can google 'host parasite' and 'symbiosis' see what all of this is about.

 

[BillTre]

There is no motive. Bacteria and virus evolve randomly, under natural selection pressures. Whatever allows a bacterium or a virus to replicate will stick.

There is also a limit to infection. If an infection is too strong and kills its host before it can replicate and infect someone else, it will go extinct.

This wikipedia post elaborates a bit on this.

It is also interesting that by controlling environmental conditions, virulency (how nasty diseases are) of pathogens can be changed via evolution.
For example, Cholera can be influenced to evolve toward less virulent forms when water sanitation is improved (see question #5).

Using "motive" as a quick term for a direction evolution takes is a common, but incorrect, interpretation of what is going on.
There is, of course, no mind with a goal and no plan to do something before it happens.

 

[Fervent Freyja]

That viruses and bacteria can affect humans, for better or worse, is really a chance outcome. We can only utilize or be invaded by less than 1% of known viruses and bacteria. Bacteria are essential to human life, we are the ones most motivated to use them to our advantage. There are many species of both but very few in comparison are actually pathogenic.

What happens to them depends upon all sorts of conditions.

 

[mktsgm]

Thanks to all who have taken pains to answer my question.

A lion preys on a deer for it is its food. Similarly I would like to know when a bacteria invades a human body, is it seeking its food?

If so what exactly is its food in our body/cells?

This is my question.