Artistic image of a double helix strand of DNA with virus particles in the background and foreground. The virus particles are spheres covered in projecting spikes.

Researchers have used ancient DNA to trace how Marek's Disease Virus evolved to become more deadly. Image credit: BlackJack3D, Getty Images.

Published

15 Dec 2023

Ancient DNA reveals how a chicken virus evolved to become more deadly

An international team of scientists led by geneticists and disease biologists from the University of Oxford and LMU Munich have used ancient DNA to trace the evolution of Marek's Disease Virus (MDV). This global pathogen causes fatal infections in unvaccinated chickens and costs the poultry industry over $1 billion per year. The findings, published today in the journal Science, show how viruses evolve to become more virulent and could lead to the development of better ways to treat viral infections.

Viral particles – seen as circular and squiggle-like shapes – inside a human cell.

Electron Microscopy image of Marek’s disease virus particles replicating in the nucleus of an infected cell. Credit: The Bioimaging group, Pirbright Institute.

The team, which includes archaeologists and biologists, recovered and reconstructed ancient MDV sequences from archaeological chickens spanning the past 1,000 years. By comparing viral genomes derived from both modern and ancient birds, they were able to pinpoint the genetic alterations responsible for the increased virulence of the modern virus.

Based on the ancient genetic sequences, they were also able to resurrect ancient biological processes using cellular assays, demonstrating that ancient strains were significantly milder than their modern counterparts.

This breakthrough not only sheds light on the evolutionary history of MDV, but also holds promise for the development of more effective therapies against this devastating poultry disease.

This new study is based on DNA isolated from chicken bones that were excavated from 140 archaeological sites in Europe and the Near East. These ancient genomes revealed that MDV was widespread in European chickens at least 1,000 years before the disease was first described in 1907. This highlights the importance of preserving archaeological remains, especially given their power to reveal valuable insights into the evolution of virulence.

When first described, this disease only led to mild symptoms in older chickens. As chicken consumption dramatically increased in the 1950s and 1960s, MDV has continued to evolve and has become increasingly aggressive despite the development of several vaccines.

When first described, this disease only led to mild symptoms in older chickens. As chicken consumption dramatically increased in the 1950s and 1960s, MDV has continued to evolve and has become increasingly aggressive despite the development of several vaccines.
First author Dr Steven Fiddaman (Department of Biology, University of Oxford)

Professor Greger Larson (School of Archaeology, University of Oxford) co-senior author commented: 'We have seen how mitigating diseases often creates a selection pressure that increases the virulence of the virus. Being able to watch this process take place by sequencing ancient virus genomes shows just how dramatically the virulence of MDV has increased in the past century.'

Professor Adrian Smith (Department of Biology, University of Oxford), co-senior author said: 'Ancient DNA has provided us with a unique perspective on the emergence of MDV as a deadly chicken virus and may teach us lessons that are applicable to the control of other viral infections of medical and veterinary importance.'

The study Ancient chicken remains reveal the origins of virulence in Marek’s disease virus has been published in Science.

One of the ancient chicken bones used in the study. Credit: Olaf Thalmann.