Ancient Viking poop helped scientists map the genetics of a 5000-year-old parasite

Researchers from the University of Copenhagen have used fossilized eggs in up to 2500-year-old stool samples from Viking settlements in Copenhagen and Viborg to genetically analyze one of the oldest human parasites, whipworm, according to a press release published by the institution.

The study reveals the global distribution of the whipworm, which has developed a complex relationship with humans over thousands of years. The parasite strives to remain "under the radar" to avoid repelling, giving it more time to infect new people. It is already known from previous studies that the whipworm activates the human immune system and gut microbiome, which is advantageous to both the host and the parasite.

Paving the way for more effective anti-worm drugs

Even though whipworm is rarely seen in industrialized countries and has a minor negative impact on healthy individuals, the parasite is thought to infect more than 500 million people in developing countries.

"In people who are malnourished or have impaired immune systems, whipworm can lead to serious illness," says Professor Christian Kapel of UCPH’s Department of Plant and Environmental Sciences. "Our mapping of the whipworm and its genetic development makes it easier to design more effective anti-worm drugs that can be used to prevent the spread of this parasite in the world's poorest regions."

The egg capsules' incredibly resistant chitin enabled whipworms' internal DNA to remain well-preserved while the eggs were buried in moist soil. The scientists separated the eggs under a microscope, sieved them from the stool, and then exposed them to genetic analyses they had been perfecting for years in earlier investigations.

"We have known for a long time that we could detect parasite eggs up to 9000 years old under a microscope. Lucky for us, the eggs are designed to survive in soil for long periods of time. Under optimal conditions, even the parasite's genetic material can be preserved extremely well. And some of the oldest eggs that we’ve extracted some DNA from are 5000 years old. It has been quite surprising to fully map the genome of 1000-year-old well-preserved whipworm eggs in this new study," explains Kapel.

Preventing serious negative effects

The research team then examined the ancient stool samples gathered from various locations and compared them with contemporary samples received from people with whipworms from around the world. This provided them an insight into the evolution of the worm over ten-thousands of years.

"Unsurprisingly, we can see that the whipworm appears to have spread from Africa to the rest of the world along with humans about 55,000 years ago, following the so-called 'out of Africa' hypothesis on human migration," stated Kapel.

As mentioned above, a whipworm infection can have a beneficial impact on a healthy host. When it comes to severe infections, on the other hand, it can lead to dysentery, anemia, and rectal prolapse, and in children, it can impede healthy growth.

The researchers believe that this new research could help develop new ways to prevent such effects.

The findings have been published in the journal Nature Communications.

Abstract:

The neglected tropical disease trichuriasis is caused by the whipworm Trichuris trichiura, a soil-transmitted helminth that has infected humans for millennia. Today, T. trichiura infects as many as 500 million people, predominantly in communities with poor sanitary infrastructure enabling sustained faecal-oral transmission. Using whole-genome sequencing of geographically distributed worms collected from human and other primate hosts, together with ancient samples preserved in archaeologically-defined latrines and deposits dated up to one thousand years old, we present the first population genomics study of T. trichiura. We describe the continent-scale genetic structure between whipworms infecting humans and baboons relative to those infecting other primates. Admixture and population demographic analyses support a stepwise distribution of genetic variation that is highest in Uganda, consistent with an African origin and subsequent translocation with human migration. Finally, genome-wide analyses between human samples and between human and non-human primate samples reveal local regions of genetic differentiation between geographically distinct populations. These data provide insight into zoonotic reservoirs of human-infective T. trichiura and will support future efforts toward the implementation of genomic epidemiology of this globally important helminth.