Protective Efficacy of Intermediate and Intermediate Plus Infectious Bursal Disease Virus (IBDV) Vaccines Against Very Virulent IBDV in Commercial Broilers

Abstract

The evolution of very virulent (vv) infectious bursal disease virus (IBDV) has led to significant economic losses in many poultry-producing areas. Despite vigorous vaccination strategies, IBDV has been difficult to control. The protective efficacy of IBDV vaccines is traditionally evaluated in specific pathogen-free (SPF) chickens. But under field conditions, residual maternal antibody (mAb) levels may interfere with vaccine efficacy. In this study, commercial broilers with various levels of maternally derived antibodies were vaccinated with IBDV vaccines of different virulence (vaccines 1-3, intermediate; vaccine 4, intermediate plus). At an average maternal virus-neutralizing antibody (mAb) level of log2 10.8 (range 7.6-11.6) at day of vaccination, only the intermediate plus vaccine induced IBDV antibodies after 18 days, while the other intermediate vaccines did not. At average mAb levels of log2 6.7 (range 5.6-8.6) at day of vaccination, all vaccines induced circulating antibodies, although the onset of antibody production differed significantly between strains (P < 0.05). While the intermediate plus vaccine induced enzyme-linked immunosorbent assay antibody levels already at 14 days postvaccination (PV), the intermediate vaccines induced significant antibody levels 28 (vaccines 1, 2) and 35 (vaccine 3) days PV. The time of IBDV antibody induction correlated with the onset of bursa lesions. The severity of lesions was comparable between vaccines 1, 3, and 4 (lesion score 4), while vaccine 2 induce only mild lesions of score 1 in 23% of the tested birds. Despite the induction of antibodies, none of the tested vaccines fully protected against challenge with vvIBDV. All challenged birds had either significantly higher bursal lesion scores or a higher IBDV antigen load in the bursa or sometimes both in comparison with nonchallenged birds (P < 0.05). Our study demonstrates that the evaluation of IBDV-vaccine efficacy is difficult in commercial broilers. For the first time, it was shown that the onset of bursa lesions and recovery of IBDV-vaccinated broilers is delayed in the presence of mAb in comparison with SPF chickens but not suppressed as previously assumed. At the time of challenge, vaccinated birds may still have significant bursa lesions and may lack target cells for IBDV-challenge virus. To be able to evaluate vaccine efficacy in commercial broilers, parameters such as intrabursal IBDV-antigen load should also be considered in conjunction with bursa lesion scores.

Evaluation of immune responses by live infectious bursal disease vaccines to avoid vaccination failures

“…Vaccination plays an important role in the successful control of the disease [1,2]. Live attenuated vaccines form the most employed type of vaccine at fi eld level.…”

“…Live attenuated vaccines form the most employed type of vaccine at fi eld level. The emergence of variant or newer strains of the virus in the recent times has been reported to cause vaccination failures [2][3][4]. Moreover, the various attenuation levels of commercially available live vaccines for infectious bursal disease virus (IBDV) lead to varying levels of immunosuppression increasing the birds' vulnerability to various infections.…”

Evaluación De La Protección Conferida Por Un Programa De Vacunación Contra La Enfermedad De Gumboro en Pollos De Carne Aplicando La Fórmula Deventer

“…Recientemente, estudios realizados por Rautenschlein et al (2005) sugieren que la protección contra el virus de desafío puede estar mediada por una "bursectomía" viral inducida por el virus vacunal y que en pollos con presencia de anticuerpos maternales, la seroconversión al virus de la EIB puede retrasarse pero no suprimirse; así mismo, que la protección contra el virus de desafío se debe a la falta de células blanco (células B) ocasionada por el virus vacunal, impidiendo de esa forma la replicación del virus de desafío. Kim et al (1999) demostraron que la replicación del virus de la EIB se acompaña de una infiltración de células T en los sitios de replicación viral.…”

Current Status of Veterinary Vaccines

“…Data from large-scale field trials for this vaccine have not yet been reported, but those studies may encounter difficulties in maintaining high efficacy. This is because these tightly regulated recombinant vaccines cannot easily adapt to meet the emergence of very virulent strains of both IBDV and MDV, apparently induced by the comprehensive numbers of vaccinations performed against these diseases (81,146).…”