Further studies on the use of a polymerase chain reaction test for the diagnosis of infectious coryza

Further information is reported on the use of a polymerase chain reaction (PCR) test for the diagnosis of infectious coryza in China. The majority of sinus swabs taken from artificially infected chickens and stored in glycerol-enriched phosphate-buffered saline were still positive by PCR after storage for 180 days at either 4°C or -20°C. Storage of swabs in either saline or nutrient broth was not as effective. Traditional culture failed to detect H. paragallinarum after storage for 3 days, regardless of storage medium or storage temperature. With dry swabs, the PCR could detect H. paragallinarum after storage for 7 days or longer at either 4°C or -20°C, while traditional culture could not. In PCR tests on 64 artificially-challenged chickens, all were positive by PCR at the six sampling dates up to 18 days post-challenge. Traditional culture gave a similar result. Both PCR and culture detected 50% or less of chickens as positive at 21 and 24 days post challenge. Antibiotic treatment reduced the ability of both culture and the PCR test to detect H. paragallinarum. The value of the PCR test and its superiority over traditional culture for the diagnosis of infectious coryza has been confirmed in these experiments