Abstract: 【Objective】 This experiment was conducted to determine the cause of morbidity and mortality of breeding geese in a goose farm in Guizhou,and provide reference for the prevention and treatment of mixed infection of multiple pathogens in breeding geese.【Method】 Clinical symptoms,necropsy observation,tissue section observation,bacterial isolation,culture and identification,and PCR detection of 6 common waterfowl viruses (Duck plague virus (DPV),Duck circovirus (DuCV),Avian influenza virus(AIV),Goose parvovirus (GPV),Duck viral hepatitis virus (DHV) and Avian Tambusu virus (TMUV)) were performed on the affected gray geese.Furthermore,the similarity analysis,capsular serotype identification,drug sensitivity test and pathogenicity test of the pathogenic bacteria were carried out,and the pathogenicity of the isolated virus was detected.【Result】 The head and neck of the affected gray goose were enlarged,and there were gray-yellow necrotic foci on the surface of the liver,and hemorrhagic spots on the surface of the heart and lung.The results of tissue sections showed that the affected gray goose had obvious lesions in liver,lung and kidney.The isolated bacterial colonies were gray-white,like dew drops with smooth surface.Gram staining showed short red rod-shaped negative bacteria.Wright’s staining showed highly stained coccobacillus at both poles.The results of biochemical tests showed that the isolated strain was positive for glucose,fructose,mannitol and maltose.PCR detection and 16S rRNA gene identification results showed that the isolated strain amplified a 460 bp Pasteurella multocida specific gene Kmt1.The similarity of 16S rRNA gene sequence between the isolate and NCBI reference Pm strains was 98.6%-99.3%,which indicated that Pm isolate was identified as Pasteurella multocidal (Pm).The Pm isolate was identified as A capsular strain by serotype analysis.The Pm isolate was susceptible to norfloxacin,gentamicin and gentamycin,and moderately susceptible to vancomycin.The minimum lethal dose (MLD) of Pm strain to mouse was less than 5 CFU.The PCR and sequencing analysis of the virus showed that the affected gray geese were infected by Duck plague virus (DPV),the UL6 gene sequence of the DPV isolate shared 98.9%-100% similarity with the reference DPV strains of NCBI.After three passages of blind transmission from duck embryos,DPV was detected by PCR in allantois fluid.Duck embryo fibroblasts (DEF) were inoculated with DPV.After 9 h,DEF shranked,and attached DEF fell off or formed syncytia after 24 h.The median tissue culture infective dose (TCID₅₀) of DPV isolate was 2.88×10^-9/0.1 mL.【Conclusion】 In this study,the infected grey goose was finally diagnosed as mixed infection of DPV and Pm,and one virulent Pm strain of capsular serotype A and one virulent DPV were isolated.The results of this study could provide scientific basis and technical support for the prevention and control of diseases caused by Pm and DPV infection of waterfowl,etiological investigation and multi-combination vaccine.

Key words: goose; Pasteurella multocida type A; Duck plague virus; isolation and identification; characteristics of pathogens