Gardin Y. et al., 57th Western Poultry Disease Conference, 2008.
The successful immunization of chickens against IBD in the field is challenged by several issues:
- The residual level of MDA is variable, or unknown at the time of vaccination; if too high, it may interfere with the vaccine; as a consequence, the actual vaccine take is frequently uneven throughout the flock; optimum vaccination date calculation needs to run ELISA test in sera that is regarded as expensive, and therefore is very rarely done.
- The administration technique (mainly, drinking water) by itself is risky; its success depends upon the quality of the drinking water used, the successful neutralization of chlorine before introducing the vaccine, the homogeneous delivery of the vaccine solution throughout the building, and the need that every chicken takes its proper dose of vaccine. As a consequence, suboptimal vaccination procedures are not rare.
In some poultry producing companies, the rate of vaccination failure due to the above-listed issues can reach 30 to 50% of the flocks.
The development of an antigen-antibody immune-complex vaccine, namely Cevac® Transmune, was driven to address those issues by providing a totally new approach in vaccinating against IBD:
- The vaccine is applied in the hatchery using automatic injection equipment, which can easily be calibrated and regularly checked to deliver a constant dose, with a high speed, and with a minimal stress to the birds; the vaccination is either done at hatch, by subcutaneous route under the skin of the neck, or in ovo at 18 days of embryonation.
- The immune-complex formulation makes this vaccine out of the reach of the MDA; as a consequence, the vaccine take is ensured, whatever the MDA level is.
Basically, Cevac® Transmune is a mixture, in well-defined proportions of the attenuated, classic type Winterfield 2512 strain of IBDV with a hyperimmune antiserum. They are produced in SPF embryonated hen eggs and in SPF chickens, respectively. The final product is freeze-dried.
Following injection in chicks, the immune complex is trapped by the follicular dendritic cells of the spleen, and the virus is gradually released. As a consequence, as soon as the residual level of MDA is suitable for vaccine take, the released virus will be able to colonize the bursa, replicate and induce an active immunity.
This vaccine has already been extensively tested in laboratory and in field conditions for safety and for efficacy. For instance, large scale field trials were conducted in Brazil in 20 million broilers (1,200 flocks): compared to the traditional vaccination program, the technico-economic performances were systematically improved by using Cevac® Transmune, because of a better control of IBD; in a few instances, the performances were similar. The vaccine take was consistently demonstrated using several laboratory tests in Cevac® Transmune-vaccinated flocks, whereas it was irregular and heterogeneous in the conventional vaccination programs.