Question: How could the parasite affect the human body?

Divya Venkatesh answered on 13 Mar 2014:

Let me count the ways – there are so many! Depends on the parasite.
Large parasites like worms stay in the intestine and probably eat all our food :), lay eggs etc.

Small ones like the trypanosomes can pretty much go anywhere they like by being carried around in our blood. The can cause red blood cells (RBCs) to be destroyed, causing tiredness (called anaemia) . Some small ones hide inside some of our body cells which are much bigger than them – obviously those cells will lose their function after being hijacked this way.

Parasites also release their waste and other material in the body which can be toxic to us – we have to put more effort into clearing these toxins and that takes a toll on us too.

And some devious ones like this one called toxoplasma gondii (we call it toxo for short) can also affect our behaviour by affecting levels of hormones like testosterone or brain chemicals like dopamine. Trypanosomes, once they get into the brain, can also cause people to lose their co-ordination, get confused and disturb their sleep cycle (from which the disease African sleeping sickness gets its name).

Parasites don’t always kill. Sometimes we don’t even know we have them because there are no symptoms. But they stay in us, as unwelcome guests and use our body for their survival, usually a great cost to our health.