Evaluation of a PCR test for the detection of Haemophilus paragallinarum in China.

The application of a recently described PCR test for the detection of Haemophilus paragallinarum in China is described. The test was used to examine a total of 127 chickens sourced from a challenge trial (38 chickens), a respiratory disease-free experimental chicken farm (50 chickens) and eight farms with suspect infectious coryza (IC) outbreaks (39 chickens). The PCR results were compared with traditional culture. The PCR detected 14/14 infected birds in the challenge trial as compared with 13/14 for culture. The 50 chickens from the disease-free experimental farm were all negative by both PCR and culture. PCR yielded 15/39 birds and 6/8 commercial farms positive as compared with 8/39 birds and 4/8 farms positive by culture. All farms positive by PCR had chickens showing the typical clinical signs of IC, indicating that culture failed to confirm coryza on two farms that had the typical clinical signs of the disease. Although chickens on two commercial farms were thought initially to be suffering from coryza, detailed clinical examination yielded no birds with typical clinical signs. The 12 chickens examined from these two farms were negative by both PCR and culture. The results suggest that the PCR test for H. paragallinarum is a suitable alternative to culture even under the typical field and laboratory conditions that operate in China.