Ancient research helps the present
New information about the biology and behavior of these sneaky little parasites may help find ways to prevent their spread, according to scientists.
“In people who are malnourished or have a compromised immune system, the slimehead can lead to serious illness,” says zoologist Christian Kapel from the University of Copenhagen.
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“Our mapping of the tapeworm and its genetic evolution facilitates the design of more effective anti-worm drugs that can prevent the spread of this parasite in the world’s poorest regions.”
Although tapeworm is now rare in industrialized parts of the world, according to the CDC, it is estimated to infect up to 795 million people worldwide, especially in areas with poor sanitation.
Lloyds Bank coprolite: petrified human faeces dug up by archaeologists from a Viking site at Coppergate, England. Contains pollen grains, cereal bran and many eggs of tapeworms and worms (intestinal parasites)Source: Wikimedia Commons, Linda Spashett Storye book, CC BY 2.5
It reproduces quickly and lasts
Its eggs pass through human faeces and can be transmitted by the fecal-oral route, when contaminated faecal matter enters soil or water, which is then ingested by another host.
Once the tapeworm eggs reach the safety of the new host’s intestinal tract, they hatch, and the female worms begin laying additional eggs continuously at a rate of up to 20,000 per day as soon as they reach adulthood. They can live up to a year, producing huge numbers of offspring – which are then excreted in the faeces to continue the cycle.
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“The eggs lie in the ground and develop for about three months. After ripening, they can survive even longer in the wild because they wait for a new host to consume them, in whose digestive tract they then hatch,” explains Kapel. “Their entire life cycle is adapted to survive in the soil as long as possible.”
It is this resilience in soil that allowed the team to sequence ancient DNA found in ancient fossilized human poo. The eggs have a shell made of hard chitin, adapted for long-term survival in the soil environment, in which the DNA contained in it is preserved.
The dung hid treasures
Thus, the researchers were able to sequence the eggs, not the dried bodies of the adult worms, recovered from the sites Viking settlements in Viborg and Copenhagen as well as from locations in Latvia and the Netherlands.
They studied a total of 17 different ancient samples under the microscope to isolate the eggs, which they then separated from the surrounding fossil matrix of the dung and subjected to genetic analysis.
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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 stilts spread from Africa to the rest of the world together with humans about 55,000 years ago, consistent with the hypothesis of human migration out of Africa,” says Kapel.
A model in the Viking Museum (Vikingemuseet) in the Danish city of Aarhus shows what the city might have looked like during the Viking AgeSource: Wikimedia Commons, Leif Jørgensen, CC BY-SA 4.0
It can be beneficial in moderate amounts
The results suggest that the parasite has adapted to the human body rather than going against it, which helps it go unnoticed, live out its life cycle and spread to as many hosts as possible.
It is also possible that, at least in some cases, a mild case of tapeworm infection can have a beneficial effect on a healthy host. For example, studies have shown that slime increases the diversity of healthy gut bacteria and reduces the number of bacteria associated with poor pig health.
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However, with a severe infection, the consequences are more unpleasant and can include dysentery, anemia and rectal prolapse, and in children can prevent healthy growth. New research may help find new ways to combat it, according to scientists.
“During the Viking era and the deep Middle Ages, hygienic conditions were not at a high level, and there was no proper separation of kitchen and toilet facilities,” says Kapel.
“This gave the minnow a much better opportunity to spread. Today it is very rare in the industrial part of the world. In less developed areas of the world, unfortunately, there are still favorable conditions for the spread.”