** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** INFECTIOUS BURSAL DISEASE VIRUS (IBDV) INFECTS CHICKENS AND IS OF MAJOR SIGNIFICANCE TO THE US POULTRY INDUSTRY. THE VIRUS CAUSES PRODUCTION LOSSES, AND CAN CAUSE BIRDS TO HAVE SUPPRESSED IMMUNE RESPONSES, WHICH THEN RENDERS THEM MORE SUSCEPTIBLE TO OTHER INFECTIONS, INCLUDING SOME THAT CAN BE SERIOUS TO THEIR HEALTH, LEADING TO FURTHER PRODUCTION LOSSES, AND SOME THAT CAN ALSO INFECT PEOPLE, FOR EXAMPLE SALMONELLA OR AVIAN INFLUENZA, WHICH ARE A RISK TO PUBLIC HEALTH. ENSURING OPTIMAL CONTROL OF IBDV IN POULTRY FLOCKS THEREFORE HAS AN ADDED BENEFIT BY IMPROVING THE CONTROL OF THESE SECONDARY INFECTIONS.NEW VARIANTS OF CONCERN OF IBDV MAY ARISE THAT CONTAIN CHANGES (MUTATIONS) IN THE SURFACE OF THE VIRUS THAT MEAN ANTIBODY RESPONSES INDUCED BY IBDV VACCINES ARE LESS EFFECTIVE, WHICH CAUSES VACCINES TO FAIL. THE DELMARVA (DMV) REGION IS A MAJOR POULTRY PRODUCING REGION OF THE USA, HOWEVER, THE LAST TIME A STUDY WAS CONDUCTED TO DETERMINE WHAT IBDV VARIANTS WERE CIRCULATING IN THE REGION WAS DONE 16 YEARS AGO. IN THE PRESENT PROPOSAL, OUR FIRST OBJECTIVE IS TO UPDATE THIS INFORMATION BY DETERMINING WHAT IBDV VARIANTS ARE CIRCULATING IN THE DMV NOW, AS WELL AS DETERMINING HOW MUCH DISEASE THEY CAUSE AND HOW EFFECTIVE VACCINES ARE AGAINST THEM.VARIANTS MAY HAVE SEVERAL MUTATIONS PRESENT ON THEIR SURFACE. HOWEVER, SOME MUTATIONS MIGHT HAVE MORE OF AN EFFECT ON ANTIBODY BINDING THAN OTHERS, AND SOME MUTATIONS MIGHT THEREFORE BE MORE IMPORTANT THAN OTHERS IN TERMS OF VACCINES FAILING. IN OUR SECOND OBJECTIVE, WE PLAN TO DETERMINE WHICH MUTATIONS ARE CRITICAL IN CAUSING A VACCINE TO FAIL, AND THEREFORE WHICH MUTATIONS SHOULD BE INCLUDED IN NEW, UPDATED VACCINES.IN ADDITION TO THE GRADUAL ACCUMULATION OF MUTATIONS OVER TIME (A PROCESS KNOWN AS ANTIGENIC DRIFT), IF BIRDS ARE SIMULTANEOUSLY INFECTED WITH TWO OR MORE STRAINS OF IBDV, THE VIRUSES CAN SHUFFLE THEIR GENES AROUND TO PRODUCE A NEW STRAIN IN A PROCESS KNOWN AS REASSORTMENT. HOWEVER, LITTLE IS KNOWN ABOUT HOW REASSORTMENT OCCURS IN IBDV, OR WHAT FACTORS PROMOTE, OR LIMIT IT. IN OUR THIRD OBJECTIVE, WE PLAN TO DEVELOP A SYSTEM FOR STUDYING HOW REASSORTMENT OCCURS, AND THEREFORE DETERMINE THE FACTORS THAT DRIVE OR CONSTRAIN IT. WE HOPE THAT IN THE FUTURE THIS COULD LEAD TO MORE METHODS TO STOP REASSORTMENT IN IBDV.