A close look at the toilets of the past and the excrement of the Vikings has provided a new perspective on the relationship between humans and the worms that parasitized them.

By extracting DNA from a range of sources, including “archaeologically speaking latrines” containing the excrement of Vikings dating back 2,500 years, researchers have reconstructed the genome of one of the oldest known human parasites.

The findings show that trichocephalus (Trichuris trichiura) has been living and adapting to humans for at least 55,000 years.

New information about the biology and behavior of these hidden little parasites will help develop methods to prevent their spread, the researchers said.

One of the oldest human parasites

“In people who are malnourished or have a compromised immune system, trichocephalus can lead to serious illness,” says zoologist Christian Kapel, from University of Copenhagen.

“Mapping the trichocephalus and its genetic development facilitates the design of more effective anti-worm drugs that can be used to prevent the spread of this parasite in the poorest regions of the world,” adds the researcher.

Although the worm is now rare in industrialized parts of the world, it is estimated to infect as many as 795 million people globally, according to the CDC, especially in regions with poor sanitation.

How is trichocephalus transmitted?

Its eggs pass in human faeces; they can be transmitted by the fecal-oral route, when contaminated faecal matter enters soil or water, which are then ingested by another host.

Once safely in the intestinal tract of a new host, the egg hatches and the female worms will lay eggs continuously at a rate of up to 20,000 per day once they reach maturity. The trichocephalus can live up to a year, thus producing a large number of offspring, which are then expelled in the feces to continue the cycle.

“The eggs lay in the soil and develop for about three months. Once mature, they can survive even longer in the wild as they wait to be consumed by a new host, in whose digestive tract they will hatch,” explains Kapel.

“Their entire life cycle is adapted to survive in the soil as long as possible,” says the researcher, quoted by Science Alert.

What role did Viking excrement play in the discovery?

It is this durability in the soil that allowed the team to sequence the ancient DNA found in fossilized Viking droppings. The eggs have a hard chitin shell, preserving the DNA inside, adapted to survive for a long time in the soil environment.

So it was the eggs, not the dried bodies of the mature worms, that the researchers were able to sequence, obtained from Viking settlement sites in Viborg and Copenhagen, as well as sites in Latvia and the Netherlands.

A total of 17 different ancient samples were studied under a microscope to isolate the eggs, which were then sifted from the surrounding fossil matrix of droppings and subjected to genetic analysis.

Viking excrement has been compared to modern excrement

The team also examined contemporary samples from humans around the world, as well as monkeys, to compare them to ancient genomes.

“Unsurprisingly, we can see that trichocephalus appears to have spread from Africa to the rest of the world with humans around 55,000 years ago, following the so-called ‘out of Africa’ hypothesis of human migration,” says Kapel.

The results suggest that the parasite has adapted in ways to work with the human body, rather than against it, to remain undetected, completing its life cycle outside and spreading to as many hosts as possible.

The worm could also have beneficial effects

It is also possible that, at least in some cases, a mild case of hookworm infection may have a beneficial effect on a healthy host. Studies have shown, for example, that pig trichocephalus increases the diversity of healthy gut bacteria and decreases bacteria associated with poor health in pigs.

But for a severe infection, the consequences are rather unpleasant, including dysentery, anemia and rectal prolapse, and in children can inhibit healthy growth. This new research, scientists say, may help provide new tools to prevent this.

Why was trichocephalus widespread in Viking times?

“During the Viking Age and up until the Middle Ages, there were not very good sanitary conditions or well-separated cooking and toilet facilities,” says Kapel.

“These things gave the trichocephalus much better opportunities to spread. Today, trichocephalus is very rare in the industrialized part of the world. Unfortunately, favorable conditions for the spread still exist in the less developed regions of the world”, concludes the researcher.

The research was published in Nature Communications.

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