**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** CHICKENS ARE COMMONLY INFECTED WITH A VIRUS, INFECTIOUS BURSAL DISEASE VIRUS (IBDV), THAT CAN DAMAGE THEIR IMMUNE SYSTEMS. AS A RESULT OF THIS REDUCED IMMUNE CAPACITY, WHEN A CHICKEN IS INFECTED WITHINFLUENZA VIRUS (IAV)THEY MAY HAVE MORE SEVERE DISEASE OVER A LONGER TIME, MAY PRODUCE MORE VIRUS TO INFECT NAIVE BIRDS, AND MAY BE MORE SUSCEPTIBLE TO INFECTIONS FROM WILD BIRDS THAN CHICKENS WITH A FULLY FUNCTIONING IMMUNE SYSTEM. IBDV CAN ALSO INFECT WATERBIRDS THAT ARE THE RESERVOIR HOSTS OF IAV. THIS STUDY WILL EXAMINE HOWIBDV AND ITS IMMUNE SYSTEM EFFECTS WILL CHANGE IAV TRANSMISSION AND EVOLUTION IN POULTRY, AND ON THE SHEDDING OF OTHER VIRUSES IN WATERBIRD POPULATIONS. THIS INFORMATION WILL THEN BE USED IN TRANSMISSION AND SURVEILLANCE COMPUTER SIMULATION MODELS TO UNDERSTAND THE IMPACT OF IBDV EXPOSURE ON AN IAV OUTBREAK IN POULTRY AND HOW LONG IT MIGHT TAKE TO DETECT THAT OUTBREAK. IBDV AND ITS EFFECT ON IMMUNE FUNCTION MAY ALSO ALTER THE EVOLUTION OF IAV WHICH WILL BE ASSESSED IN THIS WORK.MOREOVER, A WILD WATERBIRD POPULATION IN WHICH IBDV HAS BEEN DETECTED WILL BE USED TO DETERMINE THE PREVALENCE OF THE VIRUS AND HOW IT AFFECTS THE IMMUNE SYSTEMS OF WILD WATERBIRDS IN THE UK, AND THE CONTRIBUTION IT MAKES TO THE TRANSMISSION OF OTHER VIRUSES.