Using faecal samples from Viking latrines, researchers at the University of Copenhagen have genetically mapped one of the oldest human parasites, the whipworm. The mapping reflects the global distribution of the parasite and its interaction with humans, a delicate relationship that can make us healthier or sicker.
Using fossilized eggs in faeces up to 2,500 years old from Viking settlements in Denmark and other countries, researchers from the Department of Plant and Environmental Sciences at the University of Copenhagen and the Wellcome Sanger Institute (UK) made the largest and most thorough genetic analysis of one of the oldest parasites found in humans, the whipworm.
The study, published in Nature Communications, presents completely new knowledge about the parasite’s development and prehistoric distribution. This knowledge can be applied to efforts to prevent drug resistance of the parasite and its future spread.
The study suggests that humans and the parasite have developed a delicate interaction over thousands of years in which the parasite tries to stay “under the radar” to avoid being repelled, allowing it more time to infect new people. From other studies, whipworm is known to stimulate the human immune system and gut microbiome, to the mutual benefit of both host and parasite.
while whipworm (Trichuris trichiura) is now rare in industrialized countries and mostly causes minor problems in healthy individuals, with the parasite estimated to affect 500 million people in developing countries.
In people who are malnourished or have a compromised immune system, whipworm can cause serious illness. Our mapping of the whipworm and its genetic evolution facilitates the design of more effective anthelmintic drugs that can be used to prevent the spread of this parasite in the world’s poorest regions.”
Professor Christian Capel, UCPH Department of Plant and Environmental Sciences
Fossilized toilet faeces from Copenhagen and Viborg
Eggs, not worms, allowed researchers to examine the genetic material of whipworms thousands of years old. Thanks to the extremely durable chitin in the egg capsules, their internal DNA was well preserved while the eggs were buried in moist soil.
By examining fossilized stool samples previously found in the latrines of Viking settlements in Viborg and Copenhagen, the researchers isolated the eggs under a microscope, sifted them from the feces and subjected them to advanced genetic analyses, which the researchers had been perfecting for years in previous studies.
“We’ve known for a long time that we can detect parasite eggs up to 9,000 years old under a microscope. Lucky for us, the eggs are designed to survive in the soil for long periods of time. Under optimal conditions, even the genetic material of the parasite can be preserved extremely well. And some of the oldest eggs we’ve extracted some DNA from are 5,000 years old. It was quite surprising to completely map the genome of 1,000-year-old well-preserved whipworm eggs in this new study,” explains Christian Capel.
The researchers examined archaeological samples of feces from several sites. These ancient genetic samples were compared with modern samples obtained from people with whipworms from around the world. This has provided researchers with an overview of the worm’s genome and its evolution over ten thousand years.
“Not surprisingly, we can see that the whipworm appears to have spread from Africa to the rest of the world together with humans around 55,000 years ago, following the so-called ‘out-of-Africa’ hypothesis of human migration,” explains Christian Capel.
It can live undetected in the intestines for months
A whipworm can grow five to seven centimeters in length and live unnoticed in the intestines of a healthy individual for several months. During this time, it continuously lays eggs, which are excreted in the feces. In people with weakened immune systems, worms can cause a wide range of gastrointestinal diseases, malnutrition and even stunting in children.
The worms are transmitted by the faecal-oral route, meaning microscopic parasite eggs in the soil can be spread in drinking water or food, then ingested through the mouth of a new host.
“The eggs lie in the ground and develop for approximately three months. Once mature, the eggs can survive in nature even longer while waiting to be consumed by a new host, in whose digestive tract they will then hatch. Their entire life cycle is adapted to survive in the soil as long as possible,” explains Christian Capel.
As such, the golden years for these worms in our part of the world were when our toilet and kitchen conditions, as well as personal hygiene, were vastly different than today.
“During the Viking Age and the Middle Ages, one did not have much sanitation or well-separated cooking and toilet facilities. This has allowed the whipworm to spread much better. Today it is very rare in the industrialized part of “Unfortunately, favorable conditions for its spread still exist in the less developed regions of the world,” says Christian Capel.
- The new study provides the first in-depth and complete genetic mapping of the whipworm. Until now, only limited segments of the genome were known.
- The parasite spread from Africa to the rest of the world with our human ancestors.
- Among other things, the researchers collected samples of feces with whipworm eggs from Viking settlements in Denmark, Latvia and the Netherlands.
- The ancient genetic samples were compared to modern samples from people with whipworms from many different countries in Africa, Central America, Asia and Europe.
- The US Center for Disease Control (CDC) estimates that 604-795 million people are infected with trichuriasis worldwide. Source: Pullan, RL, Smith, JL, Jasrasaria, R. & Brooker, SJ (2014) Global number of infections and burden of disease from soil-transmitted helminth infections in 2010. A parasite. Vectors 7, 37.
- The study was led by the University of Copenhagen’s Department of Plant and Environmental Sciences, Section of Organismal Biology and was done in collaboration with the Wellcome Sanger Institute (UK).
University of Copenhagen – Faculty of Natural Sciences
Doyle, SR, et al. (2022) Population genomics of ancient and modern Trichuris trichiura. Nature Communications. doi.org/10.1038/s41467-022-31487-x.