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.

Two outbreaks of fowl cholera on a multiage free-range egg farm were investigated. The outbreaks occurred in 1994 and 2002. A total of 22 strains of Pasteurella multocida were available for study, 11 from the 1994 outbreak and 11 from the 2002 outbreak. Lesions typical of acute fowl cholera were seen in the 1994 outbreak, whereas both acute and chronic fowl cholera occurred in the 2002 outbreak. The isolates were examined in an extended phenotypic typing methodology, by a P. multocida–specific polymerase chain reaction (PCR), by the Heddleston somatic serotyping scheme, and by restriction endonuclease analysis (REA) typing using the enzyme HpaII. All 22 strains had the same phenotypic properties, all were confirmed as P. multocida by PCR, all were Heddleston serovar 4, and all had the same REA pattern. The results indicate that these 2 outbreaks were caused by the same clone of P. multocida–-despite the 8-year time period between the outbreaks.

Two monoclonal antibody-blocking enzyme-linked immunosorbent assays (B-ELISAs) were developed to detect serovar-specific antibodies to Haemophilus paragallinarum. One assay detected antibodies against serovar A and the other antibodies against serovar C. The assays were evaluated with sera derived from disease-free chickens as well as chickens experimentally immunized and/or challenged with H. paragallinarum strains 0083 (serovar A), Modesto (serovar C), or HP31 (serovar C). When tested with 440 negative sera (170 from a specific-pathogen-free and 30 from each of nine commercial layer flocks), both tests gave only a single false-positive reaction. The use of the B-ELISAs with the experimentally produced sera showed the assays to be serovar specific. With the exception of one serum, the serovar A B-ELISA detected antibodies only in the chickens vaccinated with 0083. Similarly, with the exception of one serum, the serovar C B-ELISA detected antibodies only in those chickens vaccinated with Modesto or those chickens challenged with HP31. Overall, the serovar A B-ELISA had a specificity of 99.7% and a sensitivity of 78.7%, whereas the serovar C B-ELISA had a specificity of 99.8% and a sensitivity of 64.7%.

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