US-UK Collab: The consequences of transmissible vaccines on disease ecology and pathogen evolution: Marek's disease virus as a case study

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Decades of evidence from Human and Veterinary Medicine has undoubtedly demonstrated the important role of vaccination in the control of infectious diseases. Transmissible vaccines, or self-disseminating vaccines, are vaccines capable of transmitting between individuals. Such vaccines, by nature of their ability to disseminate to hosts that were themselves not directly vaccinated, show substantial promise for interventions in wildlife populations, because each administered vaccine has the potential to reach otherwise inaccessible potential hosts. They may also be useful on farmed populations such as fish or chickens where vaccinating every animal will be difficult. Moreover, such vaccines might be capable of persisting in the animal population over time, reducing the urgency to vaccinate every time populations turn over, such as during reproductive seasons or between farm cohorts. However, the effects of such transmissible vaccines on the virus dynamics and evolution of pathogens, as well as potential recombination have not been examined. This project is developed from the findings of the previous EEID grant, where we found that the more efficient Rispens vaccine against Marek's disease is transmissible between birds. So the concept of the investigation is to examine more about the transmission dynamics and protection of transmissible vaccines that spread between birds. As part of the project, we will investigate whether transmissible vaccine can also drive virus evolution to greater virulence and whether such vaccines can contribute to recombination. The key question we will try to answer using controlled experiments in chickens as to whether transmissible vaccines will make things better or worse. So far a number of theoretical studies on transmissible vaccines have not given conclusive answers. We believe that the efficient transmissible vaccine model in Marek's disease will be valuable to examine how the theory and empirical data can be combined to ask what the overall consequences of transmissible vaccines are on disease ecology and evolution.