A potential system for the isolation and propagation of porcine deltacoronavirus using embryonated chicken eggs

Porcine deltacoronavirus (PDCoV) is a novel swine enteropathogenic coronavirus that leads to acute diarrhea/vomiting, dehydration, and mortality in seronegative neonatal piglets. As widely known, attempts to culture porcine enteropathogenic coronaviruses, such as PDCoV and porcine epidemic diarrhea virus, in cells have been proven to be difficult. This study aimed to establish an efficient and cost-effective culture system for PDCoV using embryonated chicken eggs (ECEs) to enable future vaccine production and efficient virus isolation from infected animals. The inoculation of samples into the allantoic cavity of 3- to 7-day-old ECEs yielded efficient virus propagation even from porcine fecal samples. Virus propagation in 2- and 8-day-old ECEs were confirmed in 30.0 % and 11.1 % of the samples, respectively. This indicates that susceptible cells rapidly develop in 2-day-old ECEs and differentiate to mature cells that are nonsusceptible to PDCoV in 8-day-old layer chicken ECEs. Furthermore, our study demonstrated that PDCoV can be passaged in 6-day-old ECEs with high viral replicative efficiency. This technique for propagating PDCoV using ECEs is a powerful tool that could be utilized for PDCoV vaccine development and virus isolation from poultry, livestock, and wild animals.