Evaluation of early onset of protection with an intermediate live IBD vaccine
containing the LC-75 strain
Willem Dekkers1, Sjaak de Wit1, Irene Jorna1, Sarah Betz21
GD Animal Health, Deventer, the Netherlands.2
Elanco Animal Health, France. Contact: sarah.betz@elancoah.com
Introduction and Objectives
Infectious bursal disease (IBD) is a widespread immunosuppressive viral disease of chickens causing an enormous economic impact to the poultry industry Due to its effect on health and performance of the birds, associated with the high resistance and ubiquitous nature in the environment of the virus, IBD control depends on biosecurity, maternally derived IBD antibodies (MDA) and a vaccination strategy The correct choice of the IBD vaccine depends on the local epidemiological situation and the objective is to provide the chicks with an early protection against IBD virus as soon as the MDA levels start to drop
The aim of this study was to evaluate early onset of protection generated by a commercial live IBD vaccine containing the intermediate LC-75 strain (AviPro® Precise, Elanco Animal Health), against a very virulent IBD virus (vvIBDV) challenge performed at 0, 3, 5 and 7 days postvaccination
Material and Methods
120 SPF broilers were randomly allocated into six groups of 20 birds based on the different treatments, including a negative and a positive control groups (figure 1) :
- 4 groups were vaccinated with an IBD intermediate vaccine (AviPro® Precise) at 7, 9, 11 and 14 days of age respectively via oral administration, and challenged at 14 days of age with a vvIBDV strain (groups 1, 2, 3 and 4)
- Unvaccinated group was challenged at day 14 with the same vvIBDV strain (group 5, positive control)
- Unvaccinated group remained unchallenged (group 6, negative control)
The birds were observed at least daily during the duration of the experiment and clinical signs were recorded The birds were sacrificed at 28 days of age and bursas were collected for histological examination to determine the Bursal Lesion Score (BLS) by using the Muskett Score1 , in order to measure the degree of damage to the bursas
Main results
Clinical signs due to the vvIBDV challenge were present in the group 4 (vaccinated and challenged at day 14) and in the group 5 (positive control) : it consisted in ruffled feathers or poor conditions justifying euthanizing the birds for welfare reasons
The groups 1, 2 and 3 that had been vaccinated with AviPro® Precise at 3, 5 and 7 days before the vvIBDV challenge did not show any clinical signs
In line with this, the groups 1, 2 and 3 presented significantly lower bursa lesion scores (p-value = 0 000) than the groups 4 and 5, by performing a Tukey Multiple Comparison test Groups 1, 2 and 3 showed significantly higher bursa lesion scores (p-value < 0 01) than the negative control, according to the expected lesions for an intermediate live vaccine It confirms that AviPro® Precise was able to protect the bursa against the vvIBDV challenge as early as 3, 5 and 7 days postvaccination
Discussion
As chickens are most susceptible to field IBDV infection in their first weeks of life, active immunity to the virus has to be induced early after hatching Based on this study, vaccination with the LC-75 strain (AviPro® Precise, Elanco Animal Health) via drinking water confers fast protection against clinical signs, bursa lesion and mortality as early as 3 days after vaccination In addition to the active immunity development after vaccination, this early protection can be explained by the occupation of the bursa cells by the IBD vaccine virus, also known as competitive exclusion