Gumboro disease control: Vaccination of the broilers

The characteristics of this challenge (age, severity, consequences, etc.) will vary from poultry house to poultry house, but the disease challenge will definitely occur.

In this situation, it is understandable that vaccination should aim at both protecting the broilers and preventing the challenge from getting out of control, that is, at ‘controlling’ the Gumboro Disease.

Key approaches that should be considered for complete Gumboro Disease management:

• Vaccination of the breeders, to transfer Maternal Antibodies to the chicks
• Vaccination of the broilers
• Biosecurity
• Diagnostic and surveillance
• Environment management

Broiler vaccination

For the very initial protection of the chicks, it means the first 2 weeks of age, the MDAs (Maternal delivered antibodies) will be essential. But after the decrease of the MDA level the chick should build up their own active immunity.

To generate the active immunity, the name of the game on controlling IBD will be through vaccination. By blocking the bursa, by the replication of the vaccine virus, and this way preventing the field strains from infecting the chick.

The Figure below shows what the objectives of Gumboro vaccination programme should be.

For this, a live virus must be used, so that this block actually occurs. The strain used in the immune-complex IBD vaccine, as the W2512,  must be attenuated and maintain its invasiveness without generating any kind of permanent damage to the cells of the bursa. It is important to note that the lymphoid depletion generated by intermediate or intermediate plus strains, in which a decrease in bursa size is observed, is physiological and transient, not impacting the immune system of birds.

Immune-complex vaccine

At the same time, this virus must be protected by antibodies (Virus Protecting Immunoglobulins VPI) so that the release occurs at the right time, and the inactivation of this vaccine virus does not occur, as in the Immune-complex IBD vaccines. A correct balance between the IBD virus and the anti IBDV antibodies is of crucial importance for the efficacy and safety of these vaccines.

The immune-complex vaccine, as Transmune, have the ability to fully colonise the bursa, protect against all field IBD viruses and overcome MDA; some of the key advantages of the immune-complex vaccines. The vaccine take occurs when the MDA level decreases to a point that allows the vaccine virus to be released and to reach the bursa of Fabricius. From this moment on, the vaccine strain will replicate in the bursa of Fabricius and the chicken will be immunised against any type of IBD virus. The fact that the virus is covered by VPI´s is important to maintain safety and stability in chickens with varying levels of maternal antibodies. In case of low levels of MDAs, replication of the vaccine virus will occur earlier, and in birds with higher levels of MDA, it will occur later. In all birds thus adapted according to the most appropriate time for replication, and thus onset of active immunity.