Serologic response to Haemophilus gallinarum in artifically infected and vaccinated chickens.

Serologic responses to Haemophilus gallinarum (HG) were compared in chickens artifically inoculated with living HG and vaccinated with HG bacterin, using tube agglutination (AGG), hemagglutination-inhibition (HI), and agar-gel precipitation (AGP) tests. Infected and vaccinated chickens differed markedly, as did infection routes early after treatment. HI response was delayed and lower in chickens infected intranasally than in vaccinated chickens. Both AGG and AGP responses peaked sooner than HI. AGP response was earlier in infected chickens, but later in vaccinated chickens. A maximum of three lines were observed. All which appeared for vaccinated chickens were similar to those for inoculated ones. A residual line remaining for very long periods for inoculated and vaccinated chickens appeared near the side of well of the HG antigen. The duration of symptoms following HG infection had no correlation with HI, AGG, and AGP titers. From these results, the HI test seems not to be the only serological diagnosis of HG infection in the field.