Persistence and Tissue Distribution of Infectious Bursal Disease Virus Serotypes 1 and 2 in Turkeys

Two experiments were conducted to determine the persistence and tissue distribution of serotypes 1 and 2 of infectious bursal disease virus (IBDV) in specific-pathogen-free and vaccinated turkeys. In Experiment 1, three groups of 2-wk-old turkey poults, including a negative control group, were used. In groups 1 and 2, 13 poults in each group were challenged with either serotype 1 (STC) or serotype 2 (OH) strains using an inoculum of 10(4) 50% embryo infectious dose (EID50)/0.2 ml/bird. Thymus, bursa, spleen, kidney, lungs, liver, pancreas, caecum, and breast and thigh muscles were sampled at predetermined intervals. The bursal tissues from birds inoculated with either serotype were reverse transcriptase-PCR (RT-PCR) positive up to 21 days postinoculation (DPI). In both groups virus isolation from bursas was possible up to 14 DPI. Except for the bursas and spleens in birds inoculated with serotype 1 and bursas in birds inoculated with serotype 2, all other tissues were RT-PCR negative. In Experiment 2, five groups of turkey poults were used. At 4 wk of age, group 1 was challenged with a serotype 1 STC strain and group 2 with serotype 2 OH strain using an inoculum size of 10(2) EID50/0.2 ml for both serotypes. Groups 3 and 4 were vaccinated at 2 wk of age using an inactivated serotype 1 IBDV vaccine. At 2 wk postvaccination, groups 3 and 4 were challenged with STC and OH strains respectively. From group 1, bursal, spleen, and liver tissues were RT-PCR positive up to 14 DPI; breast muscle and kidney tissues were positive up to 7 DPI; and lungs and pancreatic tissues were positive up to 3 DPI. From group 2, bursal tissues were RT-PCR positive up to 14 DPI and lung tissues up to 3 DPI. All of the tissue samples collected from groups 3, 4, and 5 were RT-PCR negative. Virus could not be isolated from RT-PCR positive bursal homogenate. In this work, it was confirmed that the virus persisted in the bursa longer than in any other tissues. The difference in the results between Experiments 1 and 2 could be due to the age of poults at vaccination and the higher inoculum size used in Experiment 1. This study indicates that turkeys are more resistant to IBDV as compared to chickens. Viruses of serotypes 1 and 2 infect turkeys and persist in bursal tissue for 14 days and RNA was detected up to 21 days.