Epidemiological Survey Of G Anatis Infection In Chicken Flocks And Infection And Transmission Characteristics Of Epidemic Strain In Experimentally Infected Chicks And Ducklings

Gallibacterium was recently established as a new genus within thefamily Pasteurellaceae Pohl1981. The type species of Gallibacterium is G. anatiswhich is a common organism of the upper respiratory and lower genital tract ofpoultry. Disease associated with this microorganism is related to egg peritonitis,dearease in egg production, and occasionally increase in mortality. In recent years,there were a few studies on infection and transmission characteristic of G. anatis inexperimentally infected SPF chicks and ducklings and serology of G. anatis. The aimof the investigation was to estimate and compare the seroepidemiological proportionsof G. anatis in chickens from different farms in Hebei province and to compare theinfection of G. anatis in healthy chickens at different ages. In addition, the aim of thepresent study was to provide the infection and transmission characteristic of G. anatisin experimentally infected SPF chicks and ducklings and to examine the airbornetransmission of G. anatis.An epidemiological survey of G. anatis infection in chickens using agglutinationtest in latex was carried out on667sera samples collected from10different cities inHebei province. The results showed that G. anatis infection was common in all10chicken flocks in different areas of Hebei province and that a mean percentage ofserologically positive to G. anatis was48.60%. The seroprevalence of G. anatisserotype Ⅰ, Ⅱ and Ⅳ was29.54％,29.69%and22.16%, respectively. There wasa certain difference in the seroprevalence of G. anatis among different cities. Amongthe10cities, the infection rates of Zhangjiakou and Shijiazhuang were relativelyhigher, with value of72.73％(Zhangjiakou) and80.95％(Shijiazhuang).A stratified vertical-sectional study consisting of different day-old healthychickens (1day old,3days old,5days old,8days old,9days old,10days old,12 days old,13days old,16days old,25days old,29days old,35days old,55days old,75days old,85days old,120days old,160days old,170days old and390days old)in different farms was performed to estimate the prevalence of G. anatis. Twenty birdswere sampled by tracheal and cloacal swabs in each flock. The isolated strains werecharacterized by PCR. The results showed that G. anatis infection was common in allchicken flocks in different ages. G. anatis were widely distributed within thecommercial chicken production systems. A significantly higher number of trachealswabs were positive compared with cloacal swabs. G. anatis isolated from thesmallest days of age is13days. G. anatis isolated from chickens within30days wrealmost non-haemolytic G. anatis, but elder than the30-day-old chickens mainlyinfected with haemolytic G. anatis. A total of133G. anatis strains were isolated inthis experiment and105G. anatis strains were lyophilized.To investigate the epidemiological characteristics of G. anatis, four day-old SPFchicks were infected with the G. anatis isolated from natural cases. Bacteria in organsof the SPF chicks post infection were detected and identified by the morphology, PCR,fluorescence quantitative PCR and histology, respectively, and serum antibody tierswere detected by ELISA. The results showed that no clinical signs were observed inexperimentally infected birds, however, histologic examinations of liver, lung andtrachea revealed lesions in all infected chickens. Three days post infection (p.i.) and2days post cohabiting infection of G. anaits, the G. anaits was isolated and identifiedfrom SPF chicks, and it still to be detected at96days p.i. Results of G. anaitsdetection of organs by fluorescence quantitative PCR showed that bacterial amount intracheal from both infected birds and cohabiting birds were the highest, about106copies/mg. This study showed that chicks can be infected with G. anatis as early as4day-old and the bacteria can spread by cohabiting, long-term carrying and excluding.ELISA detection results showed that the peak titers of antibodies in infected birds andcohabiting birds appeared at47days p.i. and32days after cohabiting, respectively,which lasting2to3weeks. Antibody levels of infected birds and cohabiting birdswere higher than control birds, significant differences(P＜0.05). Antibody wasproduced slowly and the duration of peak was short after infection. This studyprovided a reference basis on epidemiology, pathogenesis research and formulatingprevention of Gallibacterium anatis.To investigate the epidemiological characteristics of G. anatis, fourteencommercial ducklings were infected with the G. anatis isolated from a chicken. The sample of tracheal and cloacal swabs from all ducklings were collected for bacterialcultivation on blood agar base with5%sheep blood to ensure freedom fromGallibacterium infection. Fourteen1-day-old ducklings were divided randomly intothree groups. The quantity of infected birds, cohabiting birds and control birds was7,4and3, respectively. A sample of tracheal and cloacal swabs from all ducklings werecollected for bacterial cultivation on blood agar base with5%sheep blood every dayafter they infected with G. anatis. The results showed that commercial ducks can beinfected with G. anatis as later as33day-old and the bacteria can spread by cohabiting,successive carrying and excluding in36to40day-old. Compared with SPF chickens,ducks might be less susceptible to infection than chickens.To determine the possibility of airborne transmission of G. anatis, two groups of565-day-old SPF chickens were used, having been screened and found negative forGallibacterium organisms. One group was inoculated intraperitoneally with6.7×109colony-forming units of G. anatis strain YU-PDS-RZ-1-SLG. The other group was fedin the same henhouse with the infected group, but didn’t touch each other. A sampleof tracheal and cloacal swabs from two groups of SPF chickens were collected forbacterial cultivation on blood agar base with5%sheep blood every day after beinginfected with G. anatis. The isolated strains were characterized by PCR. The resultsshowed that the group of non-inoculated with G. anatis can be infected with G. anatisat6days p.i, which was evidence of airborne transmission of G. anatis.