Ancient chicken remains reveal the origins of virulence in Marek’s disease virus

Abstract

The pronounced growth in livestock populations since the 1950s has altered the epidemiological and evolutionary trajectory of their associated pathogens. For example, Marek’s disease virus (MDV), which causes lymphoid tumors in chickens, has experienced a marked increase in virulence over the past century. Today, MDV infections kill >90% of unvaccinated birds, and controlling it costs more than US$1 billion annually. By sequencing MDV genomes derived from archeological chickens, we demonstrate that it has been circulating for at least 1000 years. We functionally tested the Meq oncogene, one of 49 viral genes positively selected in modern strains, demonstrating that ancient MDV was likely incapable of driving tumor formation. Our results demonstrate the power of ancient DNA approaches to trace the molecular basis of virulence in economically relevant pathogens.

Editor’s summary

Marek’s disease virus (MDV) causes tumors in chickens and has increased in virulence over the past century. Fiddaman et al . studied ancient DNA from chickens to reveal the evolutionary history of this once mild disease (see the Perspective by Duchene). They sequenced MDV DNA from 15 ancient chickens, finding that these strains were basal to modern ones and identifying multiple fixed genetic changes. Testing the ancient version of the gene Meq , a regulator of tumor formation, the authors found that virulence was greatly reduced compared with modern versions. These results shed light on the evolution of virulence in a major disease in modern agriculture. —Corinne Simonti

Abstract

Functional paleogenomics reveals the molecular basis for increased virulence in Marek’s disease virus.