Rise of antibody titer following vaccination

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.