Researchers at Penn State and the U.S. Department of Agriculture have identified 10 regions in the genome of Marek's disease virus that are likely linked to increased virulence, according to an Aug. 3 announcement. The findings could inform future vaccine development aimed at preventing more severe outbreaks in poultry.
Marek's disease is a highly contagious herpesvirus that primarily affects chickens, causing tumors and paralysis but does not infect humans. Widespread vaccination since the 1970s has reduced its impact on the poultry industry, but some strains have evolved greater virulence and can evade existing vaccines.
The research team sequenced genomes from 65 strains of Marek's disease virus collected between 1962 and 2016, classifying them into four categories based on severity and ability to overcome vaccine protection. By comparing these sequences, they found nearly 800 sites with single-letter DNA differences among strains as well as several insertions or deletions. A family tree constructed from these data showed that all highly virulent strains shared a common ancestor.
Alejandro Ortigas-Vasquez, graduate student at Penn State and first author of the study published July 29 in Science Advances, said, "We found that all of the highest virulence strains in our sample shared a common ancestor. So, somewhere in this grouping of strains, a mutation or set of mutations must have occurred to allow them to break through vaccine protection. This narrows the search for DNA variants responsible for the most virulent strains." He added, "We found 10 genomic variants that were statistically associated with virulence... The strongest of these associations was with a type of DNA variant called a tandem repeat where a segment of DNA gets duplicated. The next step will be to test the function of these variants."
Co-author Andrew Read said, "This work shows the importance of sustained, collaborative research... That foundational knowledge is what ultimately will enable us to develop better tools to protect animal health and food production."
The study was funded by multiple agencies including programs supported by the National Science Foundation, National Institutes of Health, U.S. Department of Agriculture under award numbers R01GM105244 and R01GM140459, as well as support from Pennsylvania Department of Health Commonwealth Universal Research Enhancement Program.
