I would be grateful if somebody could tell me about the reasons to consider behind the rise of antibody titer other than field challenge? How can we diagnose field challenge? Are there any clinical signs? Thanks and regards.
Question has 3 parts:
1. The rise of antibody titer other than field challenge?
Antibody formation is specific to an antigen - no antigen exposure, no antibodies. Other than a field challenge antibodies will rise with vaccination. Also, in case of latent infection if the agent is reactivated as a result of stress or immunosuppression, it may cause rise in antibodies.
2. How can we diagnose field challenge?
Detect antigen - PCR.
Detect antibodies - paired sera, 14 to 21 days apart, to see rise in antibodies.
3. Are there any clinical signs?
An infection may go un-noticed (no clinical signs or subclinical disease) or may result in disease (clinical signs) - depends on host-parasite interaction.
Thank you so much professor for your response and valuable information . Actually sir I observed that the second titer after 3 weeks is high but not higher than the first titer. Do u mean a raising antibody in paired sera or the sera are high in convalescent than in acute sera
Salah Mohammed Example: First blood sample is taken on 1-March from a Layer flock House-1/Pen-3 for routine seromonitoring or at suspecting some problem (such as egg drop). Second sample is taken 2-3 weeks apart from the same House/pen. This is paired blood sample.
Antibodies are determined in the two samples, ideally on the same Elisa plate. Result may be 3 possibilities:
1. Antibody titre decreased (from 4500 in the first sample to 3000 in the second sample). This means a that the flock is not facing field challenge during the last 2 weeks.
2. Antibody titre increased (from 4500 in the first sample to 10,000 in the second sample). This means field challenge is still present and the agent is multiplying in birds (birds remain asymptomatic or become clinically sick, depends on host-parasite interaction).
3. Antibody titre has not changed (from 4500 in the first sample to 4300-4600 in the second sample). This may be a persistent low grade field challenge in the area.
REMEMBER! this situation applies to antibody titre for which vaccination is NOT done.
Prof if the flock was vaccinated against ND and IB by Ma5 &clone30 and the mean titer was found higher than the base line value post 3 weeks of vaccine application then vaccinated again for the second time against ND &IB with the same vaccine and the mean titer post 3 weeks was found higher than the base line value but less in value than the first one could we implicate interaction of other respiratory agents like mycoplasma and improper application of vaccine
My past experience: compared with any other ND-IB vaccine, Ma5&clone30 gives a higher titre. If the baseline was not built on Ma5 &clone30, one expects a higher titre than the baseline. Furthermore, titre is highest ~3 weeks post vaccination.
If the gap between two vaccinations is too short or second vaccine is administered in the presence of high titre, I do not expect further increase in titre (increase in antibodies in response to antigen is not limitless). Slight decrease may be expected due to antigen binding.