Saturday, September 26, 2020

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!


  1. "...Parasites can be used as unique markers to investigate host evolutionary history, independent of host data. Here we show that modern human head lice, Pediculus humanus, are composed of two ancient lineages, whose origin predates modern Homo sapiens by an order of magnitude (ca. 1.18 million years). One of the two louse lineages has a worldwide distribution and appears to have undergone a population bottleneck ca. 100,000 years ago along with its modern H. sapiens host. Phylogenetic and population genetic data suggest that the other lineage, found only in the New World, has remained isolated from the worldwide lineage for the last 1.18 million years. The ancient divergence between these two lice is contemporaneous with splits among early species of Homo, and cospeciation analyses suggest that the two louse lineages codiverged with a now extinct species of Homo and the lineage leading to modern H. sapiens. If these lice indeed codiverged with their hosts ca. 1.18 million years ago, then a recent host switch from an archaic species of Homo to modern H. sapiens is required to explain the occurrence of both lineages on modern H. sapiens. Such a host switch would require direct physical contact between modern and archaic forms of Homo."

    Reed DL, Smith VS, Hammond SL, Rogers AR, Clayton DH (2004) Genetic Analysis of Lice Supports Direct Contact between Modern and Archaic Humans. PLoS Biol 2(11): e340.

  2. Speaking of South Park, one of the most recent episodes is completely focused on the human microbiome. You're going to want to check it out, Ugo!




Ugo Bardi is a member of the Club of Rome, faculty member of the University of Florence, and the author of "Extracted" (Chelsea Green 2014), "The Seneca Effect" (Springer 2017), and Before the Collapse (Springer 2019)