Why were medieval monks so susceptible to intestinal worms?

Also to be avoided: Piss-chips - ie shared bar food/ snacks.

As far as I know, you can get some parasites (not sure about Ascaris specifically) just from walking around barefoot.

I know they aren't really that dangerous unless you have a really high worm load, or you're unlucky and one ends up in a part of your body where it doesn't normally live, but their lifecycle is thoroughly disgusting and terrifying. Definitely something I've stayed up at night freaking out about at a few points in my life.

I wonder how repulsive it actually was to people 1000 or 5000 or 10000 years ago though. In the wild – especially in the tropics – intestinal parasites are incredibly common in mammals, presumably including our ancestors. The invention of cooking must have reduced the parasitic load among hominins, however, as well as the discovery of soap. Various cultural taboos on eating or handling specific types of animals almost certainly originate from the desire to avoid parasites as well. Also, base parasitic load is reduced for people living in cooler climates, so worm infections may have become more yucky to Europeans not as accustomed to them.

There are lots of places today in the 3rd world where you shouldn't eat uncooked food (salad).

Are there effective best-practices to sanitize human waste for manuring? I’ve skimmed the “Humanure Handbook” which suggests a combination of composting (aerobic decomposition) and time (about one year). Are quicker and more energy-intensive options, like charring, equally effective at sanitization without removing plant nutrition?

Kudos for the "quest NPCs" joke.

My understanding is that they analyzed remains from Cambridge cemetery, meaning they were probably city-dwelling people and not peasants, so less prone to agricultural works where you catch the worms.

My suspicion is that villagers kept farm animals and mostly used their feces, while monks did not and utilised their own

Move to SE Asia and they are still quite common. It's pretty usual to "deworm" yourself with medicine 1 or 2 per year.

But I did a bit more reading on it and apparently infection rates are dropping fast and most cases are in rural areas. If you live in city, the infection numbers are pretty low.

For anyone curious, the (modern) guideline for humanure is to let it sit/compost for two years before using it, for the purpose of letting any parasites in it die. This is compared to 3-6 months for eg chicken manure (which is primarily, IIRC, about "mellowing" the fertilizer ie letting it undergo some chemical changes).

The headline also over-generalizes the results: perhaps using human excement as fertilizer was more common at Cambridge, but the study did not look at other monasteries (or other Medieval time frames). I wonder whether there is a reason to expect that farming practices were shared between monasteries.

It is hard for me to fathom that this article was written around such insignificant numbers .

11/19 Monks

8/25 Commoners

One bad meal could swing those numbers and adding to that the monks were more communal than individual families so more likely to affect them all.

Would combustion affect poop’s fertilizing qualities, or spread bad stuff around in the steam and smoke?

I am not sure human feces burn as well as herbivore manure.

Cow and horse feces look pretty different from human feces, drier and "herbal", and I would be surprised if they share the same combustive properties.

Sheep/goat/rabbit also seem naturally much drier than human tho I've never investigated their internals :)

Edit: on a second thought, cow shit is not particularly dry

It's quite hard too dry out faeces in the British climate. It's common in hot countries.

> I'm surprised that most people didn't pre-burn their dried feces before using it as fertilizer

This paper is about incineration of sewage sludge. They consider incineration at temperatures like 700C to 900C. Seems like you end up burning 98% of the nitrogen, which is then released as gas (bottom of page 12, just before Conclusions). The output ash only contains 2% if the input nitrogen.

Kind of defeats to point of using the output as fertilizer.

https://sci-hub.se/https://doi.org/10.1021/acs.energyfuels.5...

Thanks for the clarification of how this works! :-)

That one route of infection, most typically pin worms.

Intestinal worms can transmitted a number of different ways, but it's commonly the oral-fecal contamination route where feces comes in contact with food (when feces are used as fertilizer) or water (poor waste management) which is consumed.

However, hookworm larva can penetrate intact skin. Step in a puddle with bare (or exposed feet) and you can get infected.

Yes. Two tailed test gives p=0.0854

Do enough random microscopy on enough cemetaries and you have a tale to tell every time.

I'm not really convinced there's an actual story here.

It is, when you prior is that the populations should be different with a difference in the opposite direction.

But even than the magnitude of the observed effect is so noisy ( large type m error)

Good catch!

I'm more inclined to use a Bayesian approach here because we can't be certain about the probability of either population becoming infected. The 80% Credible Intervals for the two Beta distributions overlap: [1] and [2]. So indeed, the chance that either a monk or a normal villager would get infected by a parasite could be about the same.

I'm not sure if using Credible Intervals in this way is kosher, so someone feel free to critique. Ideally, if p is the unknown probability of a villager getting infected, and q is the unknown probability of a monk getting infected, then we need the posterior distribution of p-q. We have all the data needed to estimate this; you may use either simulations or characteristic functions to do it.

[1] - https://www.wolframalpha.com/input?i=Beta%2812%2C9%29+distri...

[2] - https://www.wolframalpha.com/input?i=Beta%289%2C18%29+distri...

Barnard's test is appropriate here, because while the experimental design is a 2-way contingency table, only the columns (# villagers and # friars) are constrained, the rows (# infected/ # not infected) are not. P value was just under 0.05.

I am not sure about these specific monks, but many would eat a minimal amount of meat (and it would typically be limited variety). They believed that giving up meat is a form of penance.

This is the most parsimonious explanation to me as well, unless there is a way to groundtruth egg preservation in each location, it seems quite likely that the proportion of eggs surviving 600-800 years will vary between locations.

This was an analysis of graves though, what individual people died with. I have no idea how or if burial rights were different for monks vs regular people. (both were probably christian, though there could well have been small differences which may or may not be significant.

Can't edit previous comment but - I tracked down the actual study, the soil was indeed from graves (right under the sacrum where the bowels were) and was compared to control samples by the head or feet of the grave. The friars were buried with clothes, the laypeople in shrouds so similar deal and the sites were a few hundred meters apart so about as well controlled as you could expect, I reckon.