Detection of vvIBDV in Vaccinated SPF Chickens

The purpose of our experiment was to investigate, if apparently healthy, vaccinated chickens may be involved in maintaining and spreading infectious bursal disease virus (IBDV) in poultry environments. We aimed at simultaneous detection and identification of very virulent field strain IBDV (vvIBDV) as well as vaccine strain IBDV in experimentally infected chickens. Two groups of specific pathogen free (SPF) chickens were vaccinated using the intermediate infectious bursal disease (IBD) vaccine D78. Group 1 was vaccinated at the age of one week and group 2 at the age of three weeks. Both groups were challenged with vvIBDV at the age of four weeks. A third, vaccinated, non-challenged group served as negative control. No clinical symptoms were observed in any of these groups. The chickens were euthanised and submitted to autopsy and sample preparation in groups of three at fixed intervals from the age of 28 to 44 days. Gross pathological lesions were not observed. Lymphoid tissues from the bursa of Fabricius, bone marrow, spleen and thymus in addition to cloacal- and bursal swaps were analysed by one-step reverse transcription polymerase chain reaction (RT-PCR). Positive results were confirmed by two-step strain specific duplex (DPX) RT-PCR. The vaccine strain was detected in bursa tissues from all groups, while the challenge strain was detected in few bursal as well as non-bursal tissue samples. The results indicate a possibility of replication of vvIBDV in vaccinated chickens.