Serologic Response to Haemophilus gallinarum in Artificially Infected and Vaccinated Chickens

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Abstract
Serologic responses to G. gallinarum (HG) were compared in chickens artificially inoculated with living HG and vaccinated with HG bacterin, using tube agglutination (AGG), hemagglutination-inhibition (HI) and agar-gel precipitation (AGP). 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. AGG and AGP responses peaked sooner than HI. AGP response was earlier in infected chickens, but later in vaccinated chickens. A maximum of 3 lines were observed. All lines which appeared for vaccinated chickens were similar to those for inoculated ones. A line remaining for very long periods for inoculated and vaccinated chickens appeared near the side of the HG antigen well. The duration of symptoms following HG infection had no correlation with HI, AGG and AGP titers. HI is the only suitable test for serodiagnosis of HG infection in the field.