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Avian - 2002
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| (Print Friendly Version) |
| Project Contact: | Jagdev Sharma | Funding: | $64,150 |
| P. Chary |
District:
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Unknown |
| • The Problem • Objectives • Mid-Year Progress Report • Final Report • |
The use of attenuated isolates of APV as vaccines appear to have reduced APV associated losses, although definitive data on the protective efficacy of these viruses is lacking. There is also confusion about some of the fundamental aspects of the pathogenesis of APV, including:
This research is designed to:
Update – February 2002
The protective efficacy of the APV-63 vaccine in commercial turkeys has been examined. An identical dose of APV-63 was given to two groups of turkeys. In one group, APV-63 was given in eggs at the 24th day of incubation (in ovo vaccination); in the other group, APV-63 was given at hatch.
In ovo vaccination with APV-63 did not adversely affect hatchability of eggs or livability of hatched poults. Turkeys given in ovo vaccination developed earlier and longer lasting protection than those vaccinated at hatch. APV-induced local respiratory immunity was critical for protection against respiratory challenge. Subcutaneous immunization with live APV did not induce resistance against respiratory challenge.
October 2002
Our studies enhanced our understanding of the pathogenesis of APV and provided evidence that in ovo vaccination may be used to control the disease. The results showed that in ovovaccination with the test vaccine did not adversely affect hatchability, and was successful at inducing at least eight weeks of protection against virulent APV (APV-13). Presence of antibodies did not, however, correlate with protection.
Our examinations of the mechanisms involved with the hatchling’s response to the vaccine were also valuable. Examining the effect of age on respiratory signs and the mitogenic inhibition of spleen cells revealed that clinical respiratory signs were most pronounced when the turkeys were two weeks old at exposure. Resistance to clinical disease increased with increasing age. The mitogenic inhibition of spleen cells was detected in birds exposed to APV-13 at two, four and six weeks of age, but not at eight weeks. The lymphoid cells infiltrating the Harderian gland of APV-exposed turkeys comprised both B and T cells. T cells recovered from the Harderian gland were activated and secreted increased levels of cytokines following in vitro stimulation with a T cell mitogen.