Abstract: In December 2014,a group of 4 weeks old broilers died in a large-scale chicken farm in Hebei province.The clinical symptoms of the ill and diseased chicken were depression,dyspnea,joint swelling and claudication.In order to diagnose the disease,a systematic analysis was conducted by laboratory diagnostic methods that included histopathological observation,bacterial isolation,PCR detection,drug sensitive test and animal pathogenicity experiment.The histopathological observation results showed that hemorrhage in the lung,the edema of heart and liver,a large number of heterophil granulocyte infiltration.Bipolar stained brevibacterium was observed under the microscopy.The PCR amplification results of Pasteurella multocida KMT-1 gene and avian reovirus σB gene were positive by using specific primers.The isolated Pasteurella could be lethal to mice and the isolate was highly sensitive to ceftriaxone and cefoperazone.Combination with the above laboratory test results and the clinical symptoms,we confirmed that the cases were mixed infection of avian reovirus and Pasteurella.

Key words: avian reovirus; Pasteurella; mixed infection; diagnosis