Immune-complex vaccines complement vector vaccines to cool IBD challenge
When it comes to protecting flocks from infectious bursal disease (IBD), immune-complex vaccines offer unique attributes that make them attractive as part of a rotation strategy with recombinant HVT-IBD vaccines.
Often used in cases of high field-virus pressure, immune-complex vaccines are useful for “cooling down the house” and keeping the field pressure low for subsequent flocks. They do this by colonising the bursa and blocking early replication of field virus. The introduction and repeated use of these vaccines can repopulate a house with vaccine virus, creating a “diluting” effect – the overall viral load in the environment is reduced, thereby decreasing the risk of infection and spread of the IBD virus within the flock.
Vector and live vaccine comparisons
Because the virus particle is coated with antibodies to form the immune-complex vaccine, it cannot be immediately neutralised by maternally derived antibodies as conventional live vaccines can. When the maternally derived antibodies decrease over time and reach a threshold level, the vaccine virus will be dissociated from the immune complex and released as a live vaccine – a process that is delayed compared with the conventional attenuated live vaccine.
This delayed release brings at least three major advantages. First, there is a robust vaccine-induced active immune response, with the delay meaning there is no longer the high chance of neutralisation of vaccine virus by maternally derived antibodies.
Second, the onset of immunity is naturally adapted to when each individual bird is ready to respond, due to the active vaccine-induced immunity starting as the passive immunity decreases.
Finally, the delayed release helps reduce the immunosuppression often seen with the use of conventional live vaccines. Whether the birds are vaccinated in ovo or at day of age, the immune-complex vaccine gradually dissociates in the bird’s body and releases the live vaccine virus. This gradual release allows the vaccine virus to populate the bursa of Fabricius (the primary target organ for IBDV) and stimulate a robust immune response without being immediately neutralised by maternally derived antibodies.
Options for different field scenarios
IBD virus is genetically diverse, with seven different genogroups falling into classical virulent, antigenic variant and very virulent types. Different field challenges, as well as bird type, can call for different immune-complex formulations.
A Zoetis vaccine based on the Winterfield 2512 classical virus strain is one such formulation, which has been tested against a high, early IBD challenge.
In a study using chickens vaccinated in ovo with this vaccine, 100% protection was achieved after viral challenge at 13 days of age (Figure 1), highlighting that the vaccine was not only efficacious at early ages but also effective even in the absence of maternal antibodies.
Solutions for sensitive flocks
Another alternative is an immune-complex vaccine based on the V877 IBD strain, which is also considered intermediate plus and distinctly categorised as Genogroup 7. This option brings a unique mix of efficacy and safety, based on additional research.
The V877 immune-complex vaccine from Zoetis was found to break through maternal antibody titers in broiler chickens of over 1,100, determined by IBD ELISA testing. Vaccine safety also was demonstrated by giving a 10x overdose of the vaccine to SPF chickens, and although this caused lesions, they were not scored much higher than the maximal permitted scores for mild live IBD vaccines.
A rotation strategy of immune-complex and vector vaccines could offer an option for controlling IBD. In broiler chickens, immune-complex vaccines based on the Winterfield 2512 strain and the V877 strain can be used, while the V877 strain can be used in layer chickens. Reach out to your Zoetis representative to find out more.
References are available upon request.
Approved labeling for registered products can be different in various countries around the world, and not all products are approved for use in every country around the world. The information featured in this piece is based on approved product labeling in Europe. Consult your local Zoetis representative in the country where you practice for additional product information.
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