Holobiont Science: Sometimes a Little Vague, but Always Interesting

 

Holobiont science is sometimes a little vague, but always interesting. Here is an example.In this paper, http://www.zoologia.hu/list/Why_infest.pdf, Rozsa and Apari argue that head lice in humans is a useful symbiont because it generates an immune response that helps protect humans from body lice, which can be dangerous as vector for harmful bacteria. (the photo above is from the paper)

 

It is an interesting story where you learn that there are at least two types of lice living with humans. And you learn that apes have only one kind, probably because they are uniformly hairy. Rozsa and Apari go on suggesting that the "touching heads" human habit has the specific purpose of diffusing health lice in such a way to spread the immunity to body lice. Apes, they say, don't touch each other's heads because they don't have such a need. 

 

Which is, as I said, very interesting, but is it true? Honestly, it gives you the idea that the authors are piling up one hypothesis after the other, none of them being really supported by data. For instance, in the places where I live, there is no habit of touching heads as a form of salutation or an expression of friendship. Then, are we sure that apes touch heads less frequently than humans do? I don't think we have solid statistics on that point. Besides, why are body lice dangerous, but not head lice? One more mystery of holobionts! 

 

But it is nevertheless a nice idea that adds a little more to the complexity of the idea of holobionts. And the picture that illustrates the paper (in lieu of non-existing data) is truly charming. Two distinguished professors exchanging lice. Wonderful!

Where you could buy live lice in Florence, 50 years ago.

 

According to what I heard from the people who remember these things, I think I was able to locate where you could buy live lice in Florence to swallow to cure your jaundice. A typical holobiont thing to do. 

The old lady who sold these lice lived - I believe - in the house with the small arched door of this street called "Via Camaldoli." She was called "La Pidocchina," that is, "the little lady louse."

I didn't try to ring the bell to ask if someone in there still sold live lice. But, who knows?

The Truth about Lice Revealed. A new discovery about the human holobiont

 "Lice Capades," an episode of the TV series "South Park." Lice are being understood as an important part of the human holobionts and, who knows? One day they may be considered as an essential component of human health, just as gut bacteria. 

 

Today I had a little revelation on lice. I had been writing about some recent discoveries on the beneficial effects of lice on human health and I had reported a story that I heard from my wife about people swallowing live lice as a remedy for jaundice (hepatitis b). And of people in Florence selling lice just for that purpose. But I wasn't sure if it was a real story or a legend. 

But, today, I heard a talk by Maurizio Naldini, a Florentine journalist, who told several stories about the Florence of his youth. And, yes, he had met in person the woman who sold lice! It was true: people would buy lice in Florence as late as some 50 or 60 years ago. 

The curious thing about this story is that Mr. Naldini had no idea of why people bought lice and what they did with them. So, he listened with great interest to my wife telling him the story of lice being swallowed inside a wheat wafer to cure jaundice. 

In my case, hearing Mr. Naldini had a different effect. Now that I knew that the story was most likely true, then I could examine it more in depth. Of course, the idea that lice would suck out the bile of jaundice makes no sense. Swallowed lice (dead or alive) can hardly suck anything. But then, why would people do such a thing? 

Of course, there is a tradition for people paying good money to do the strangest things when they are sick and they think something can help. CBS has a list of the 15 most bizarre (and disgusting) cures ever invented, and it is surely interesting to learn about such ideas as placing a dead mouse in the mouth to cure toothaches or using crocodile dung as a contraceptive. But they don't mention lice!

Yet, even the most bizarre ideas have an origin and I think that the lice market of Florence had a justification, probably better than that of crocodile dung. It has to do with the concept of holobiont, the fact that the human body (just as that of most animals) is an incredibly complex assemblage of creatures. Most of them very small (bacteria and viruses), some a little larger (lice and others), and with the actual human organism as just one of the many, although surely the biggest. 

Now, holobionts exist, and if something exists it means there are good reasons for it to exist. Most of the creatures that populate the human holobiont are there for a reason. Maybe they are just harmless commensals but in many cases, they are useful symbionts. And that may well be the case of lice, too. 

I already mentioned a study that found "Unexpected Benefits from Lice." The little critters seem to boost the human immune system. But there may also be another benefit. You see, there are three kinds of lice inhabiting the human holobiont: the body louse, the head louse, and the pubic louse. 

Of these three, the only one that may be harmful to human health is the body louse. It may be because it is a relatively recent human parasite having developed in parallel with the use of clothing. But another study argues that the "good" head lice can be beneficial in stimulating the development of an immune response against the "bad" body lice. So, if you have (or have had) head lice, you are healthier.

Perhaps this is the key to the story of the market of lice in Florence. Ancient Florentines knew little about immunity, but they may well have noted that people who had head lice were less prone to have body lice. Perhaps even that head lice could help people get rid of body lice.  Lice don't jump around or fly, so moving from one body to another is not so easy. And so they would ask their friends and relatives if they could give a hand in passing lice to someone who was lice-deprived. Then, why not? Some enterprising people thought they might make a little cash by providing others with a commodity that was needed: lice. 

Maybe this was the origin of the legend that my wife told me. Once that lice were understood as beneficial, it was natural that they could be tested on other kinds of illnesses. Then, the placebo effect would convince people that lice were effective in curing jaundice. With the more enlightened (so to say) 20th century, lice of all kinds became anathema and a social stigma, But the idea that you could eat lice in a wafer to cure a rather stubborn illness such as jaundice remained for some time. 

It is an interesting story that goes in parallel with that of the discovery of the bacterial flora in the guts. Some people understood right away their importance and their beneficial effects, but others thought that it was not hygienic having bacteria in your guts and thought it was a good idea to get rid of them. Now, of course, you buy probiotic supplements just to get more good bacteria inside your guts. Who knows? Maybe one day it will be fashionable to buy head lice in a pharmacy in order to prime people's immune systems!

And this is the story. The more things you know, the more you discover. And so, onward, fellow holobionts!

 

Note: After publishing this post, I received a link from Jan Barendrecht to a paper that describes how swallowing lice was considered a therapy for several kinds of illness in Spain. But not just in Spain. The authors say that: 

Numerous authors show that using animal resources as therapy is a widely distributed atavistic practice [52,53], a fact that is demonstrated by the use of head louse against jaundice in distant geographical areas [54,55]. Its use is particularly common in the Hebrew culture. Izaak Walton in his famous book “The Compleat Angler” (published in 1653) records that the Jews were the first to say that swallowing live lice is a good remedy for jaundice [56]. For their part, the German rabbi Yair Bacharach (1639–1702), author of the collection of responsa known as “Havvot Yair” (“Villages of Yair”), indicates that the patient should take 8 lice taken from his/her own head–see Rosner and Bleich 2000 [57]. Ben-Ezra in 1949 recorded in Horodetz (one of the oldest Jewish communities in Russia-Poland) the introduction of lice in an omelette as treatment [58]. In Latin America there are also references to this medical practice. In this case, the remedy would have been brought by the Spanish conquistadors and assimilated by the Spanish American folk medicine in an eclectic form [9]. The recommended number of specimen to take in Chile, Peru, Guatemala and Argentina is 4 or 5 with examples found using measures such as a thimbleful [59-62].

Unexpected Symbionts: What if Your Health could Benefit from Creatures you Normally Despise?

 

"Lice Capades" (2007). An absolutely wonderful episode of the "South Park" series. The world as seen from the viewpoint of lice. Fantastic. 

In Italy, there is a legend that says you may be cured of hepatitis b (jaundice) by eating lice. It is not just a vague legend, I personally know people who swear they were cured of jaundice by doing exactly that. Apparently, in the 1960s, there were still people who sold live lice packed in a small wafer (where they got the little beasties is anybody's guess). No trace of this story can be found on the Web nowadays, I can only relate it from what relatives and acquaintances tell me. But I have no reason to doubt that it was a common belief some 50 years ago, although it may have been limited to Tuscany, or perhaps only Florence. There are reports of people eating lice in other cultures and, of course, monkeys, apes, and other furry animals do that all the time. 

About this story, let me say that I am a big fan of evidence-based medicine and I am the first to doubt this story (and, also, I never had lice in my life). But, once you acquire the concept of "holobiont," you start reasoning that lice must have accompanied the human organism for millions of years. And, if they did, there has to have been some reciprocal adaptation and -- why not? -- mutual benefit. Of course, as a human being, you won't even remotely imagine that lice may be good for your health. But are you sure? 

At this point, you start searching the web and, surprise! (or maybe not), you immediately find an article titled "Unexpected Benefits from Lice" Look, this is serious stuff, evidence-based, not old folks' tales. And they say: 

Parasites such as lice have a role in the conditioning of a 'natural' immune system and reducing the likelihood of immune dysfunctions,

Of course, that's true for mice, but there is no reason to believe that it wouldn't work for human organisms, as well. Some people have said exactly that, "lice can be good for you." Maybe that's a bit optimistic but, surely, there is no reason to fall into hysterical reactions when dealing with lice in children. In some cases, lice may be bad for your health, but the little critters are not a major threat.

So, may lice be a symbiont rather than a parasite? As usual, the boundary between the two categories is fuzzy. Likely, no creature living inside the human holobiont is 100% parasitic. Most of those that lived with us for millions of years surely have at least some beneficial effects. And let me tell you just one thing: my mother-in-law holobiont had flatworms for most of her life. She turned 100 two months ago and she is in reasonably good health for her age. Would there be a correlation? At least, you can't rule that out!

You see how ideas interlock with each other and branch out generating new ones? Once you have the concept of holobiont, you have access to a whole new host of concepts. It is the beauty of the world we live in: truly Gaia takes many forms!