Comparison of Traditional and Sequenced-Based Pathotyping of Marek's Disease Virus Field Strains
Avian Disease and Oncology Laboratory
2013 Annual Report
1a.Objectives (from AD-416):
1) To characterize contemporary Marek's disease virus strains and correlate virulence with multiple other factors. .
2)To sequence informative variable regions within the viral genome of these field strains to analyze the molecular epidemiology of these isolates.
1b.Approach (from AD-416):
The primary goal of this study is to determine if MDV has increased in virulence compared to the last comprehensive set of MDV isolates that were solicited and pathotyped nearly 15 years ago. Objective 1 addresses this goal and will also examine if virulence has changed on farms in which isolates have been previously isolated, and whether strains are evolving differently in separate geographic locations or chicken lines. In Objective 2, we will take advantage of next generation sequencing (NGS) power to molecularly characterize samples collected from farms for pathotyping. Our primary goal will be to determine if polymorphisms in the MDV genome are associated with pathotype and other measured MD-associated traits. We will also determine if MDV sequences differ among isolates from the same bird, farm, geographic location, or over time in order to gain better understanding of the evolutionary trends of the virus. These methods will provide information on the diversity of MDV sequence variation and may lead to alternative methods of pathotyping.
For Objective 1, we contacted our various stakeholders and spread the word that we are seeking samples from flocks that are experiencing current Marek’s disease problems. As of this report, we have collected blood and dander samples from flocks in Iowa, Pennsylvania, Delaware and Nebraska. We have successfully isolated 9 field isolates for pathotyping of the 18 proposed isolates, which is used to classify the virulence of the virus isolates. We expect to receive additional isolates later this year and anticipate collection of any remaining isolates needed next year. Pathotyping trials are ongoing for all current year virus isolates.
Objective 2 involves whole genome sequencing of the three most virulent isolates from the first year of the project and will commence after the completion of this year’s pathotyping trials.