الفهرس 
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Abstract
The present study was performed for molecular characterization of IBDV in Behira and Alexandria governorates, Egypt in addition to evaluate some vaccination programs adopted in the field against infectious bursal disease (IBD). A total number of 30 flocks at age 17-37 days old between April 2014 and June 2017 were investigated. Twenty flocks (66.7%) were in Behira and nine flocks (33.3%) were in Alexandria governorate. The chicken type was broiler in 26 farms (86.7%) and only 4 SASO farms (13.3%). The capacity of investigated farms ranged from 1500 to 10000 birds per farm.
The suspected IBDV samples were propagated in 9-11 day SPF-ECEs via CAM with daily observation for 5 days. Dead embryos, CAMs, embryos and chorioallantoic fluids were collected and processed to make embryos homogenates which used for molecular characterization of IBDV.
Embryo homogenate of each 30 investigated farm was tested for presence of IBDV genetic material by RT/PCR using specific primers for VP2 hypervariable region gene. Out of 30 tested samples, 12 samples were positive with percent of 40% and 18 ones were negative with percent of 60%. Out of 4 investigated SASO flocks, one was positive RT/PCR (25%) and out of 26 investigated broiler flocks, 11 ones were was positive RT/PCR (42.3%).
Sequencing analysis of selected eight positive RT/PCR isolates revealed that seven isolates were characterized as very virulent (vvIBDV) strains with 81.3-100% identity with each other and with 81.9-100% identity with very virulent Giza 2008 strain while only one isolate was characterized as classical IBDV with 100% identity with classical strain of CEVAC IBDL® vaccine.
Eight vaccination programs commonly used in the field were evaluated on 180 commercial broiler chicks which grouped into 10 groups as following:
group (1): vaccinated with HVT-IBD vector vaccine (Vaxxitek®) at 1-day-old via subcutaneous injection.
group (2): vaccinated with immune complex vaccine (Bursa-plex®) at 1-day-old via subcutaneous injection.
group (3): vaccinated with immune complex vaccine (Transmune®) at 1-day-old via subcutaneous injection.
group (4): vaccinated with intermediate-plus live attenuated vaccine (228E) at 14-day-old via eye drop.
group (5): vaccinated with intermediate live attenuated vaccine (D78) at 12, 22-day-old via eye drop.
group (6): vaccinated with inactivated vaccine at 5-day-old via subcutaneous injection with intermediate live attenuated vaccine (D78) at 12, 22-day-old via eye drop.
group (7): vaccinated with inactivated vaccine at 10-day-old via subcutaneous injection with intermediate live attenuated vaccine (D78) at 12, 22-day-old via eye drop.
group (8): vaccinated with intermediate-plus live attenuated vaccine (CEVAC IBDL) at 14-day-old via eye drop.
group (9): non-vaccinated challenged.
group (10): non-vaccinated non-challenged.
At 28 days old groups (1-8) were divided into two subgroups (A and B) per each one. Birds of only subgroup (B) of each group as well as group 9 were challenged by isolate (29) at dose of 10-2.5 EID50 / bird while other subgroup (A) remained unchallenged.
At 28 day-0ld, no active immune response has been developed in groups 5, 6, 7 and 8 while at 35 days old all groups showed active immune response. A rise in antibody titers in all groups was observed after challenge.
Vaccines used in groups 1, 2, 3 and 7 gave complete protection from mortality while none of the evaluated vaccine gave complete protection against pathological gross and microscopic lesions after challenge.
None of the evaluated vaccine gave complete protection against bursal atrophy 7 days post challenge, but group 1A showed the least bursal atrophy among all challenged groups.
Under the circumstances of this study and criteria used for evaluation of eight vaccination programs (clinical signs, post mortem gross lesions, histopathological changes, mortality rate, feed conversion rate, serology and bursal and spleen indices), one might summarize that HVT-IBD vector vaccine (group 1) gave superior protection followed by inactivated vaccine at day 10 of age with intermediate live attenuated vaccine at 12 and 22 day-old (group 7) then immune complex vaccines (groups 2 and 3) and finally inactivated vaccine at day 5 of age with intermediate live attenuated vaccine at 12 and 22 day-old (group 6), intermediate live attenuated vaccine at 12 and 22 day-old (group 5) and intermediate plus live attenuated vaccine at 14 days old (228E and CEVAC IBDL in groups 4 and 8 respectively).