Infectious bursal disease (IBD) is a contagious immunosuppressive viral infection of young chickens. Intra-cloacal approach is effective for vaccinating chicks with high maternally derived IBD antibodies; however, the vaccinal traditional dose may be unsuitable for this route. A total of 60 one-day-old specific-pathogen-free (SPF) chicks were randomly distributed into four groups. Group-1: was control and chicks in group-2: were vaccinated with 103.5 TCID50 of D78 strain/ bird via intra-cloacal route, chicks in group-3: were vaccinated with a ten-fold higher dose (104.5 TCID50/bird) and chicks in group-4: were vaccinated with a dose of 102.5 TCID50 of D78 strain/bird using same approach. IBD antibody titers were measured at the 14th and 21st days of age. The immunosuppressive effects of different doses were determined through humoral immune response to avian influenza and Newcastle disease vaccines, the relative weight of primary lymphoid organs, and histopathologically evaluated bursal lesions. The results indicated that a dose even ten-fold higher than the usual dose to SPF chicks via intra-cloacal route caused neither morbidity nor mortality. All vaccine doses induced potent immune responses against IBD, but the highest IBD antibodies titers were observed in group-4 while IBD antibodies titers were decreased with increasing vaccine doses in other experimental groups. Even the vaccinated birds showed moderate histopathological lesions and the diminutive relative weight of bursae; there was no immunosuppressive effect in the immune response to other vaccines in group-4 and transient immunosuppressive effect in groups-2 and-3. All that proves the safety and effectiveness of various intra-cloacal vaccination approach doses.

First complete genome sequencing of a DHAV-3 strain from Egypt using m-NGS.Discovery of a novel duck astrovirus co-infecting with DHAV-3.Phylogenetic analysis reveals cross-border transmission links with Asian strains of both DHAV-3 and DAstV-5.

Infectious bursal disease (IBD) remains a potential worldwide threat to the poultry industry despite several vaccination approaches. Because maternally derived antibodies (MDA) constitute a critical problem for IBD vaccination, we estimated the efficiency of the intracloacal vaccination approach in breaking through MDA. Experiment 1 determine the ability of the vaccinal strain to multiply in the bursa of Fabricius (BF) in chicks with a high level of MDA. Using real-time polymerase chain reaction, we quantified the strain in the bursae of vaccinated and non-vaccinated chicks. Experiment 2 was performed on three groups of chicks with high levels of MDA: group 1, non-vaccinated nonchallenged; group 2, non-vaccinated challenged; and group 3, vaccinated challenged. Seroconversion of IBDV was measured using enzyme-linked immunosorbent assay. Groups 2 and 3 were challenged by vvIBDV at 25 days of age. Experiment 3 studied the effect of early IBD vaccinal strain multiplication on the immune response of vaccinated and non-vaccinated chicks to other vaccines. In experiment 1, the vaccinal strain showed progressive multiplication and reached the detectable titer in BF at 12 hours postvaccination despite high MDA titer. Experiment 2 showed that chicks in group 3 had significant seroconversion against IBD. After challenge, group 3 showed significant improvements in several measured parameters compared with group 2. Moreover, results of experiment 3 proved that early multiplication of the vaccinal strain in BF has no significant effect on the immune system or immune response to other vaccines. These results proved the promising success of this IBD vaccination approach. Research Highlights

Highly pathogenic Avian Influenza (HPAI) viruses, especially the newly discovered H5N8 clade 2.3.4.4b strain, are the world's biggest concern. The HPAI virus challenge in broilers is a significant issue, especially for short-lived commercial broiler chickens. This study examined H5 inactivated vaccine regimens. Phylogenetic analysis was used to compare the genetic sequences of vaccination seeds, the challenge virus (H5N8 clade 2.3.4.4 strain), and the circulating HPAI H5N8 strain. Following this, a field investigation evaluated various vaccination schedules using the H5 inactivated vaccine against the HPAI virus in early-challenged commercial broilers with maternal immunity against the AIV-H5N8 virus. Three vaccination regimens were planned: a prime-boost regimen (days 1 and 9) in group 1 (G1), a single dose 1.5 times the manufacturer-recommended dosage on day 7 in group 2 (G2), and the routinely recommended single dose on day 7 in group 3 (G3). Weekly AI-H5 humoral immune response antibody titers were measured. Both vaccinated and unvaccinated positive controls were challenged with HPAI H5N8 virus clade 2.3.4.4b on day 28 of age. Clinical signs, Survival, and virus shedding were monitored for 10 days post-challenge. After three weeks post-vaccination (WPV), prime-boost antibody titers were significantly higher than those in single-dose groups. After the challenge, G2 and G3 had high survival rates (91.7%) but a noticeably high shedding rate following the early challenge (3-WPV), while G1 had 100% survival and negligible viral shedding. HPAI H5N8 virus protection increased with prime-boost vaccination in early challenge. These findings highlight the importance of implementing optimal vaccination programs to mitigate HPAI virus risks in commercial chicken production.Research Highlights: A phylogenetic study has proven vaccine genetic match with circulating H5N8 strains.Prime-boost vaccine regimen provided 100% survival in H5N8-challenged broilers.Enhanced immunity observed in prime-boost groups, with minimal viral shedding⁣.Single-dose groups achieved 91.7% survival and showed higher viral shedding.