I always had a very basic view of how infectious diseases work: our bodies are normally clean and free of 'bad bugs', then we touch a door handle with all of those brightly coloured rods on it (as beautifully demonstrated in those Dettol adverts) , then we get ill. But is it really as simple as this?
The answer, of course, is no. Many bacteria coexist happily with us when found in the right areas of our body; sometimes even performing beneficial roles. However, when they are accidentally moved to the 'wrong' areas of our body, they can cause us problems. Hence why it's not okay not to use the excuse: "but they're my germs anyway!" for not washing your hands after doing a number two.
But there is a class of bacteria that are known as 'opportunistic', and not because they brownnose their bosses to try to gain a promotion; this opportunism is much more sinister than that. There are bacteria who have an arsenal of weapons they can use to take advantage of any hostile situations we might be facing to gain access to other areas of the body without permission. Let me show you an example.
Neisseria meningitidis is indeed a rod shaped bacterium (one of the few things the adverts haven't exaggerated), and can be found in the throats of perfectly healthy individuals. Under certain circumstances, like a viral infection, this bacterium can move from the welcome home of the throat to the battle ground of the blood. This movement is known as bacteremia, and can lead to more fatal conditions, most notably meningitis.
So why then, if they are able to invade the blood, don't they do it all the time? And how do they even do it in the first place? Well despite what most people think, the evolutionary goal of a bacterium is not necessarily to invade the body and kill it as soon as possible; bacteria that do this in nature are actually quite unsuccessful. The most successful bacteria are that ones that can form mutually beneficial relationships with us.
If at this point you still don't believe that most bacteria are friendly, then maybe you will believe me when I tell you that there are more friendly bacteria in your colon than all of the people who have inhabited the earth, ever. So take this as a warning to be wary of any cleaning company or news provider that tries to scare you with cries of 'BEWARE OF THE BACTERIA'. If it wasn't for bacteria you'd be dead already; but I digress.
These Neisseria have developed a system for sensing their surroundings, picking their moment, and shape-shifting into a well armoured tank that can roll into the blood stream without fear of attack. The key to this magic trick lies in a weapon called an RNA thermosensor.
When you are infected with a virus, your body temperature will rise as part of its immune response to get rid of the invader. So the naughty Nesseria sees its opportunity, the RNA thermosensors physically uncoil due to the higher temperature, and are translated into proteins that are used for invasion. This carefully designed domino effect allows the bacteria to time its invasion of the blood to a time when the immune system is a state of heavy austerity; it's too busy dealing with its deficit!
So are you terrified of this invisible enemy yet? Well, you shouldn't be. It's easy for anyone writing about science, especially those with no genuine interest in research, to whip up fear in their readers who aren't from scientific background. The point I'm trying to make is: infections are much more complicated than forgetting to wipe down all of your banisters with Dettol.