Infectious coryza: cross-protection studies, using seven strains of Haemophilus gallinarum

Bacterins prepared from 7 strains of Haemophilus gallinarum were used to immunized chickens for cross-protection studies. Three distinct immunotypes were distinguished. Slight protection between immunotypes was evident for some strains. Airsacculitis could be prevented by use of these bacterins; however, prevention was related to immunotype specificity. Hyaluronic acid found in 2 strains rendered them inagglutinable in homologous antiserums. Treatment with hyaluronidase rendered them agglutinable.