RESUMEN
OBJECTIVE: To use specific real-time qPCR to determine (1) the vaccination success of Rispens CVI988 vaccine in feathers and dust; (2) persistence of Rispens infection in vaccinated layer chickens; (3) extent of co-infection with wild-type Marek's disease virus (MDV) in vaccinated layers; and (4) presence of Rispens virus in unvaccinated broiler flocks. METHODS: Feather, dust and serum samples were collected from birds aged 3 days to 91 weeks from three layer farms. qPCR was used to detect MDV and Rispens in DNA extracted from dust and feathers. Previously tested MDV-positive dust samples from 100 broiler flocks were tested for the presence of Rispens using qPCR, while serum samples were used to detect anti-MDV antibody using ELISA. RESULTS: Overall, 66% and 93% of feather and dust samples, respectively, from Rispens-vaccinated layers were Rispens-positive. Viral load in these samples varied between farms during early life, reaching readily detectable levels at 2-3 weeks of age. Vaccinated chickens maintained a high Rispens load in feathers and dust and high MDV antibody levels until 91 weeks of age. MDV infection was detected in 6.7% of feather samples from vaccinated chickens. Rispens virus was detected in 7% of samples from unvaccinated broiler flocks. CONCLUSION: Vaccine take can be measured effectively by Rispens-specific qPCR of feathers or dust from approximately 3 weeks post vaccination. Infection with Rispens is persistent, with lifelong shedding and serological response. The detectable infection rate of vaccinated chickens with MDV is low and there is preliminary evidence of escape of Rispens virus to unvaccinated flocks.
