Live vaccine boosting

摘要

Live boosting is the periodical application of a live ND or IB vaccine during lay to boost protection. While there are benefits provided by this programme live boosting is not for everyone because of the logistics of the procedure. The merits of thebiological principles involved are clear and well documented. Live boosting stimulates both cell-mediated and humoral antibody immunity, including local (eye, trachea) as well as a modest level of circulating (bloodstream) protection. Application of aninactived (killed) vaccine during the growing period following adequate live priming stimulates formation of uniformly high levels of circulating antibodies only. These high titres wane over time leaving older flocks relatively unprotected. Why is localprotection important? It has been demonstrated that immunized birds with even no measurable level of circulating antibodies are able to withstand challenge against both Newcastle and Bronchitis viruses. The local antibodies produced (Ig A's) and the localimmune cells are quite activein con trolling infection. The circulating antibodies (Ig G's) are not as effective. Unfortunately there is not a practical method to measure local antibodies or cells produced after live vaccination to estimate the achievedlevel of protection. The serotogical method known as ELISA is relatively easy to run and it measures levels of circulating antibodies. Although this technique provides a fairly good indication of the effectiveness of a vaccination programme, it cannot supply an accurate calculation of the protective level of such a programme, as it also measures some antibodies that are non-protective. This is they are not "neutralizing" antibodies. We assume that if we have high liters on ELISA test, at least part of these will protect.