The place of ancient parasites in human disease and health
Heirloom parasites have affected people since our evolution in east Africa. Piers Mitchell says there are 16 parasites in the heirloom group including roundworm, whipworm, and beef tapeworm. Others are blood parasites, such as malaria. The souvenir parasites are those picked up from animals after humans left Africa. Some parasites can be traced to changes in farming methods, as people formed closer associations with animals, and used water for irrigation. Piers Mitchell studied the remains of Richard III exhumes in 2012 and found evidence of the heirloom parasite roundworm, but says for people with good health and diet, it was unlikely to cause problems.
Robyn Williams: So, do you have worms? Could they be good for you? Are there some diseases which we've had for so long we just tick over with them and they don't matter much? Professor Piers Mitchell from Cambridge has divided such maladies into two categories.
Piers Mitchell: Well, the heirloom parasites are the group of diseases that have affected people right throughout human evolution, where we originally developed in East Africa. The other group are souvenir parasites. So in the way that you might acquire a souvenir from going on holiday somewhere different to where you live, a souvenir parasite is a way we have of describing when people migrated out of Africa, moved to new areas of the planet and then acquired new parasites from the animals that were already living in that part of the world.
Robyn Williams: Which diseases are in the first category, the ones from ancient times?
Piers Mitchell: Well, I've identified 16 particular parasites within the heirloom group that evolved with us in Africa. Some of these are parasitic worms from our intestines, such as round worm, whip worm, beef tapeworm. Some of them are parasitic worms that live in the tissues of our body such as schistosomiasis, and others are single-cell parasites that live in our blood and our liver and spleen, for example malaria and leishmaniasis.
Robyn Williams: And of the second group, the ones we just pick up, do they have a more drastic impact on us?
Piers Mitchell: Well, there are several different groups that we find. So some of these souvenir parasites are particularly problematic in Southeast Asia where they originated, and often caught from seafood, either seafood or freshwater fish, so things such as the Chinese liver fluke. Then there are the parasites that seem to have come from South America, so we have a Pacific fish tapeworm, for example. And then there are single-celled parasites such as dysentery where the evidence suggests that Entamoeba dysentery may well have actually originated in animals in Europe.
Robyn Williams: Talking about animals, we've had civilisation maybe at a time when farms were being invented and we had animals around us constantly, maybe lots of cows, certainly dogs and pigs and so on. Were they the main source of big diseases like plagues?
Piers Mitchell: I am midway in a large project specifically to investigate this where I've set up a collaboration with many archaeologists who are excavating early towns and settlements in the Middle East. And what we're finding is that in the earliest villages there were individuals with some of these heirloom parasites such as whip worm, and we have found them 7000 or 8000 BC. And then as time goes by and people introduce new farming methods such as irrigation, that's when we are starting to find schistosomiasis which is a fluke, a flatworm that is contracted by people wading in warm freshwater that is infected with the parasite within freshwater snails. And so the very fact that they are changing their farming practices and using irrigation leads early humans to be more at risk of certain particular parasites.
Robyn Williams: And of course because of farming with slurry everywhere you often had a corruption of water that used to be drinkable and pure, and people famously, not least journalists these days, turned to beers and other things which they could rely on as not giving them disease. So was water corrupted by farming quite early on?
Piers Mitchell: That's certainly something I'd like to look at, and one thing that I'm interested in is did the invention of the toilet result in a better intestinal hygiene. So there are different ways that we can of course study this, but the parasites that are spread from faecal contamination of hands, so things like whip worm and round worm, these are very much the kind of parasites we would like to see whether they become less common after cesspools and toilets are invented. We see them in the Middle East perhaps a couple of thousand BC.
Robyn Williams: Let's look at some of those heirloom diseases, because the suggestion is that our immune system got used to many of these, and as we became, as you describe, cleaner and cleaner, the body which was used to responding to the continuing presence of these parasites kept looking around wondering where they were and became, if you like, sort of hyperactive. And so you had lots of allergies develop, especially in modern times, not in the presence of parasites but the absence of them. And it has been quite extraordinary to find that when those parasites are reintroduced, people often get better.
Piers Mitchell: That's the hypothesis that has been put forward over the last 10 years or so. There's one particular paper published in Science in 2002 proposing this, and there is a certain amount of anecdotal evidence in parts of the world where parasitologists go out and clear the local population of their parasites. I've heard a number of presentations where they show how a lot of the children then start to develop allergies over the next year. But what we really need to do now is randomised trials where we can scientifically prove this link rather than just noting an association, which is what people have done so far.
Robyn Williams: Well, of course the famous anecdote is of the person who gave himself…I think it was hook worm, and found that his symptoms kind of went away, and they had been crippling before. Now he has got a kind of business selling dried out versions of his faecal matter around the world which people can take.
Piers Mitchell: I'd very much like to see a nice scientific validated approach where people can make sure whatever treatments they are getting are completely safe. And to do this we need randomised trials where the placebo effect is removed. Because if you try and do something to your own body, you know what you've done and you may find the placebo effect improves your symptoms when there is no genuine effect. And if we can do a randomised trial where people don't know whether they've taken chalk or whether they've taken a true extract from a parasite, they will be in a much better position to show scientifically whether this really works.
Robyn Williams: Theoretically could it work possibly?
Piers Mitchell: Yes.
Robyn Williams: So taking the parasite which then tells your body, yes, here is the enemy and it's under control and you don't have to get quite so hyped up with the overreactions that the body otherwise would produce.
Piers Mitchell: That's right. And the trouble with setting up this kind of research is that many people are scared about the idea of having a parasite. They feel that is a bad thing. But if people change their mind to what parasites are in the way that it's common to have a yoghurt drink with healthy bacteria in, if you can change your thoughts so that you understand the concept of a healthy parasite as opposed to one that will cause you illness, then you may well find in the future people are much more open to the idea of having those kind of parasites that don't do much harm to us and consequently might be of benefit to people with bad allergies.
Robyn Williams: Yes, I notice people were terribly upset about the fact that Richard III was found to have round worm in him. This was perfectly normal - then.
Piers Mitchell: That's right, I published that paper in Lancet last week which showed Richard III did have round worm, but it is an heirloom parasite, so it's one of those diseases that our human ancestors would have had in Africa and when they migrated out of Africa. And if you have a very heavy load of parasites, yes, that can cause symptoms and can cause problems. But if you have a good diet with plenty of food and if you only have a small number of parasites, you probably wouldn't have had any problems from those parasites being there.
Robyn Williams: How did you get access to Richard III?
Piers Mitchell: Those excavating Richard III invited me to join their project. Most of the study is done by people at Leicester but they realised they needed my expertise, partially because I am the leading ancient parasite researcher in Britain and partially because he had scoliosis and they know I have a particular expertise in scoliosis as well.
Robyn Williams: Did you find anything else in Richard III?
Piers Mitchell: Well, not only his parasites and his scoliosis but also the weapon injuries that he had and also the genetic evidence that has been studied comparing him and his ancestors to make sure that firstly we have the right individual and secondly to look at the genetics. And that is an ongoing project where people will bring out more results in the next few months.
Piers Mitchell: Dr Piers Mitchell is a biological anthropologist at Cambridge.
- Piers Mitchell
- Division of Biological Anthropology
University of Cambridge
- Robyn Williams
- David Fisher