Continuous cell lines from the muscovy duck as potential replacement for primary cells in the production of avian vaccines

Veterinary vaccines contribute to food security, interrupt zoonotic transmissions, and help to maintain overall health in livestock. Although vaccines are usually cost-effective, their adoption depends on a multitude of factors. Because poultry vaccines are usually given to animals with a short life span, very low production cost per dose is one important challenge. Other hurdles are to ensure a consistent and reliable supply of very large number of doses, and to have flexible production processes to accomodate a range of different pathogens and dosage requirements. Most poultry vaccines are currently being produced on primary avian cells derived from chicken or waterfowl embryos. This production system is associated with high costs, logistic complexities, rigid intervals between harvest and production, and supply limitations. We investigated whether the continuous cell lines CR and CR.pIX may provide a substrate independent of primary cell cultures or embryonated eggs. Viruses examined for replication in these cell lines are strains associated with, or contained in vaccines against, egg drop syndrome, Marek's disease, Newcastle disease, avian influenza, infectious bursal disease, and Derzsy's disease. Each of the tested viruses required the development of unique conditions for replication that are described here and that can be used to generate material for in vivo efficacy studies and to accelerate transfer of the processes to larger production volumes.