17.12.2023

Fiddaman et al., Science 382, 1276–1281 (2023)

A new study published in Science discusses the use of viral paleogenomics to study the origins of virulence in Marek's disease virus (MDV), a highly contagious virus that affects chickens. By sequencing MDV genomes from archeological chicken remains, researchers have discovered that the virus has been circulating for over 1000 years. 
The increase in virulence and clinical pathology of MDV infection has likely been driven by a combination of factors. First, the growth in the global chicken population since the 1950s led to more viral replication, which increased the supply of new mutations in the population. In addition, the use of imperfect (also known as “leaky”) vaccines that prevent symptomatic disease but do not prevent transmission of the virus likely shifted selective pressures and led to an accelerated rate of MDV virulence evolution. Combined, these factors have altered the evolutionary trajectory, resulting in modern hyperpathogenic strains.
The study also found that the two major modern clades of MDV were likely established before the earliest documented increases in MDV virulence in the 1920s. The article provides insights into the epidemiological and evolutionary trajectory of pathogens like MDV and highlights the potential of viral paleogenomics in understanding the origins of viral diseases.