Epidemiologic studies on infectious coryza outbreaks in northern New South Wales, Australia, using serotyping, biotyping, and chromosomal DNA restriction endonuclease analysis.

The epidemiology of 16 cases of infectious coryza, an upper respiratory tract disease of chickens caused by Haemophilus paragallinarum, was investigated in a retrospective study. The cases occurred over a 14-month period on 10 farms in northern New South Wales. The available field data indicated that the cases formed six unrelated outbreaks. The 16 isolates of H. paragallinarum were subjected to serotyping by the Page and Kume schemes and biotyping based on carbohydrate fermentation and antimicrobial drug-resistance patterns. As well, newer fingerprinting techniques--plasmid profiles, whole-cell protein profiles, immunoblots of whole-cell protein profiles and total DNA restriction endonuclease analysis (REA)--were evaluated. Antimicrobial biotyping and REA profile typing proved most useful, allowing the recognition of three groups among the isolates. The other techniques gave either limited or no subdivision among the isolates. The combined results of the laboratory study indicated that, rather than six unrelated outbreaks, the 16 isolates represented three pairs of related outbreaks. This study represents the first application of sensitive biotyping and fingerprinting techniques to outbreaks of infectious coryza. The results have established that farms can be repeatedly infected with a single strain of H. paragallinarum that re-emerges at intervals. This study also obtained the first detailed evidence that replacement stock are a major source of infectious coryza.