Location: Endemic Poultry Viral Diseases Research
Project Number: 6040-32000-074-04-A
Project Type: Cooperative Agreement
Start Date: Feb 15, 2016
End Date: Feb 14, 2020
Marek’s disease (MD), a lymphoproliferative disease of chickens caused by the highly pathogenic Marek’s disease virus (MDV) is one of the most serious chronic disease problems that costs the worldwide poultry industry $1-2 billion per year. Efforts to control this agriculturally relevant disease have focused on biosecurity, vaccination, and selection for genetic resistance. However, there is a lack of epidemiological studies that examine how the virus is spread from bird-to-bird. In particular, it is not known whether current control efforts also reduce transmission of MDV. Transmission and spread of an infectious agent like MDV depends on both (1) how susceptible non-infected individuals are, and (2) the infectivity or propensity of transmitting the infection. There is evidence for considerable phenotypic variation in infectivity for many pathogens, which may also have a genetic component. Up to now, however, obtaining reliable estimates for host genetic infectivity has proven difficult as appropriate quantitative genetics methods were lacking. Our colleagues at Roslin Institute have recently developed the theoretical framework and Markov chain Monte Carlo (MCMC) algorithms that allow us to estimate host (genetic) susceptibility and infectivity from binary disease data. In this project we will apply these to MD in poultry. Our US-UK collaborative approach to this project will leverage our US scientists’ expertise in MD pathogenesis complemented by our UK collaborators’ expertise with statistical tools and immune genetics. In this project, we hypothesize that poultry vaccinated against MD and with greater genetic resistance to MD are also less infectious, and we address the following objectives. 1. Determine to what extent poultry with genetic resistance to MD are also less infectious. 2. Determine to what extent vaccination against MD also reduces infectivity. 3. Identify phenotypic markers for host infectivity.
We will be conducting a series of experiments utilizing virus donor and contact recipient birds coming from genetically inbred chicken lines. Donor birds will be varied by MD genetic susceptibility or vaccination status. Infection rates in recipient birds will be measured at frequent time points. Duration of infectivity will be assessed in experiments where donor birds are transferred to a series of isolators with new recipient birds. Additional experiments to will include donor birds from a series of inbred recombinant congenic strains (RCS), which are derived from our inbred MD resistant and susceptible lines and enable us to quickly map QTL for infectivity. Our colleagues at Roslin Institute will perform MCMC algorithms for estimating host (genetic) resistance and infectivity that will be adapted and refined for application to the experimental data.