Parasitism

BBC Radio 4 - In Our Time, Parasitism

"[They make up] Half the world's biomass - humans have 400 parasites knocking about the most of us...

Most of the cells within your skin are not your cells - they're the cells either of parasites or of bacteria who for the time being are being helpful rather than parasitic but can switch... the proportion of cells in your body which are human are equivalent to your left leg from the knee to the toe. That's the only human cells. All the rest are other cells...

If the hosts are too successful... if you grow mice in the lab... and ensure there is absolutely no other living creature, parasite or bacteria or anything else within these mice: they're called axenic mice, then they're very very feeble and weak and they die... Many things which have been thought to be harmful parasites, almost inevitably turn out to be doing good things as well as bad things...

'The famous mitochondria... started life off at the dawn of time as an intracellular parasite, has been reduced by this battle between the host and the parasite to become an essential part of the cellular machinery but can now and again itself, tiny as it is, turn on its owner and destroy it'

'Parasites can have a positive and good'

'Trouble is, words like positive and good don't really belong in biology. It turns into theology then'...

There is a strong tie between various psychiatric conditions things like schizophrenia, depression and so on. People with those conditions are much more likely to have the toxoplasma in their brain and there are claims - and the figures are fairly impressive - that if you look at people who have been killed by dangerous driving, they are twice as likely to be have been infected by toxoplasma as is the general population...

A lot of parasites, for example some of the worms that infect our guts, lay their eggs and they come out in our feces and they go into the environment. And because those eggs then have to last survive very well in the environment in order for the next host to pick them up, they are very resistant in the environment so they got hard shells around them and so on. So that means that quite often they are very well preserved in archaeological remains...

When flush toilets first came in to Brian what did they do to Cholera? They made it worse. Because what happened was that they just pumped it straight into the river Thames...

If we were to remove all parasites quite simply in nature there would, nature would be less diverse. We would see less diversity at the genetic level, looking at traits and behaviors. Even talking about all the different ways that parasites can shape hosts' behaviors and traits and appearance and also genes. But also at the ecosystem level.

So it's been shown recently in the tropics that if there is one particular host species which is quite dominant in the community the parasites can target that species, knock it back and that would let otherwise inferior competitors to flourish. That is until they themselves become common and parasites can go after them...

There is a new wave of research showing that the microbes residing within us and ones as part of our microbiome, the microbial community that we harbor can actually provide a barrier of defense against parasitic infection"