Question: Do you know how many parasites are in the body and how they make us sick? And if you do find out could you tell me?

Clare Harding answered on 7 Nov 2014:

So this will be a long answer because this is a great question!

So in the UK you probably don’t have any parasites (unless you’ve been on holiday recently) because mostly they don’t like the cold. But you do have about 100000000000000 bacteria in you, mostly in your intestines. (That’s 10x more than human cells in you!). These bacteria don’t make you sick and are probably important in keeping you healthy, some of them even help us absorb vitamins.

But, some bacteria do make you sick and they do it in lots of very, very clever ways. I used to work on one called Legionella which makes you sick by hiding inside the cells which are supposed to kill it. Some bacteria make toxins like botulism toxin (botox) which are so powerful that 1g could kill maybe 10,000,000 people. Other bacteria can change the way they look to your body meaning they can hide and your immune system cant find them.

But back to parasites, there are a number of different parasitic diseases ranging from tapeworm when you would only have 1 parasite to ascaries or Schistosomiasis where you can have thousands. In the case of something like severe maleria, you could have between 6000 and 200,000 parasites at one time if you were very sick.