Developing vaccination programs for IBDV requires strategic use of several vaccine types.
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Developing a vaccination program for infectious bursal disease virus (IBDV) challenges should consider the severity and duration of immune suppression caused by the virus, which may require the strategic use of several vaccine types.
Timing of IBDV challenge is a key influencer on vaccination strategy. Early infections before 2 weeks of age often cause severe and permanent immune suppression (IS). From 2 to 3 weeks of age, the severity of IBDV-related IS can vary depending on concurrent stressors or other immune suppressors. The effect of infections after 3 weeks of age can be moderate and temporary but significant nevertheless if other disease challenges – such as infectious bronchitis, Escherichia coli or inclusion body hepatitis – occur during this window of temporary IS.
IBDV vaccine options
There are three distinct options for IBDV vaccination in the hatchery:
- Recombinant vaccines: modestly cushion the bursa and limit – but do not prevent – field IBDV replication.
- Immune complex vaccines: cause a “take” but also reduce field IBDV replication.
- Live vaccines: complement maternal immunity and help bridge the gap to the onset of immunity from recombinant vaccine when both are used.
Depending on virus challenge pressure and levels of maternally derived antibodies, these vaccine options can be used in rotation throughout the year to strategically achieve IBDV management goals.
Live vaccines buy time for recombinants
Live IBDV vaccines are complementary to recombinant HVT-IBD vaccines. While it is not always necessary to give live IBD vaccine(s) along with a recombinant, when field infection pressure is very high or the field virus is very aggressive, the addition of live IBDV vaccination to a recombinant program may help flocks overcome the challenge because the live vaccine virus may interfere with or block the growth of the field virus.1
The live vaccine provides rapid immunity to the most susceptible chicks with the lowest levels of maternally derived antibodies. When the vaccine virus replicates, it also creates a blocking effect on the field virus1. Delaying the field infection window buys time for immunity from the recombinant HVT-IBD to fully develop.1
Intermediate vaccines can also be applied in the first week to help the transition from passive to active immunity and delay the field pressure to allow more time for the recombinant vaccine to provide the bursal and immune system “cushion.”
Complementing recombinants with immune complex vaccines
The strength of recombinant vaccines is their cellular immune response2 and cushioning – not completely preventing infections but significantly limiting the number of cycles of infection and, therefore, tissue damage (atrophy, in this case) – which translates into protection against immune suppression from the IBD challenge.
For immune complex vaccines, besides their convenience of flock coverage with one live vaccine application, their strength is in how they limit field infection, reducing field infection pressure and amount of wild-type virus that continues to be shared in the environment.3 This means the IBD challenge levels in the field can be managed more effectively.
However, the other side of the coin is, because it’s an effective live vaccine, there will be a bursal “take” – so bursa sizes will be more variable, especially in the three- to four-week range as the vaccine is starting to infect the bursas and cause some bursal atrophy. PCR surveys are commonly used to demonstrate the reduced window of field virus replication on this type of program while bird performance is maintained.3
One way to look at recombinant and immune complex vaccines complementing each other is to play to each of their strengths for long-term sustained efficacy. One scenario might be using an immune complex vaccine for one or two growout cycles in the summer when a significant reduction in the field IBDV challenge can be achieved. Then, move back to a recombinant program during the high challenge of winter respiratory season, with a focus on cushioning the bursa and the immune system against IBD challenge.
By reducing the field infection pressure, the immune complex vaccine is likely to set up the recombinant program to be more successful the next time it is used.
Surveillance keeps you informed
Through active bursal surveillance programs, producers can monitor which IBDV strains they are dealing with, what ages those strains are challenging their birds, and how much replication and bursal atrophy is occurring (cushion effect).
With that information, an IBDV vaccination strategy can be developed using the best tools in the toolbox – recombinant, live and/or immune complex vaccines – to minimize the severity of IBDV challenge and limit immune suppression.
Article Written By: Kalen Cookson, DVM, MAM, DACPV, director of clinical research, Zoetis
References:
1 Ashraf S, Abdel-Alim G, Al-Natour MQ, Saif YM. Interference between mild and pathogenic strains of infectious bursal disease virus in chickens. Avian Dis. 2005;49:99-103.
2Boone AC, Kaser T, et al. In ovo vaccination with herpesvirus of turkey enhances innate and cellular responses in meat-type chickens: Effect of vaccine dose and strain. Vaccine 2020;38:4837-4845.
3 Data on file, Outcomes Study No. 04-15-70AJJ, Zoetis Inc.
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