Synergistic Pathogenic Effects And Diversity Study Of Escherichia Coli Of Co-infection With Avian Leukosis Virus Subgroup J And Reticuloendotheliosis Virus In Broiler Chickens

Avian leukosis virus subgroup J(ALV-J) and reticuloendotheliosis virus(REV) are retroviruses which can cause immunosuppressive and neoplastic diseases in chickens. ALV-J was first isolated in 1988 from meat-type chickens with myeloid leukosis, which is characterized by hepatomegaly, splenomegaly, and diffuse neoplastic nodules on organ surfaces. ALV-J infection has been reported in many regions of the world over the past 10 years and has caused severe economic losses in the poultry industry.Previous studies have showed that simultaneous infections by several tumorigenic viruses were very common in chickens. In fact, the co-infection of ALV-J and REV is one of the most serious simultaneous infections. Usually, REV and ALV-J cause subclinical infections leading to growth retardation and immunosuppression, which are often neglected. Avian E. coli disease can be primary disease of chickens, and also be secondary infection of mycoplasma,viral infections and other environmental factors, and it can cause high morbidity and mortality.The previous searches found that some immunosuppressive viruses single infection or co-infection could cause E. coli secondary infections in broilers, which showed typical pericarditis and peritonitis. Gao studied the synergistic effect of low pathogenic avian influenza and E. coli infection, and found a synergistic effect between MPAIV and E.coli in the aspect of pathogenic. The synergistic mechanism may be that MPAIV infection caused a degree of immunosuppression which promoting E.coli settle and multiply in the chickens.In this study, we present a systematic and in-depth analysis on the effect of co-infection with ALV-J and REV in broiler chickens and the diversity of the secondary E. coli.1、Synergistic pathogenic effects of co-infection of ALV-J and REV in broiler chickensTo study the interactions of co-infection on pathogenicity of ALV-J and REV, one-day-old commercial broiler chickens were randomly divided into five groups, which included experimental treatment groups REV, ALV-J, REV + ALV-J(high-dose [H]), REV + ALV-J(low-dose [L]), and control. The first 3 weeks, the five groups were separately bred in shielded cages with positive filtered air. After the first 3 weeks, the chickens were raised infive separate houses that were fumigated with formaldehyde before the chickens were placed.After an immune response was generated for 3, 4 and 5 weeks, the sera of all the tested chickens were collected for haemagglutination inhibition testing to determine the concentrations of NDV and AIV-H9 antibody. At 6 weeks of age, samples of the thymus,burse of Fabricius, and spleen were excited and weighted. The results showed that the co-infection of ALV-J and REV could induce more growth retardation and higher mortality rate than ALV-J or REV single infection(P < 0.05). Chickens co-infected with ALV-J and REV also showed more severe immunosuppression which was manifested by significantly lower immune organ to body weight ratios and lower antibody responses to Newcastle disease virus and H9-avian influenza virus(P < 0.05). For the E.coli secondary infections, the mortality associated with E. coli infection in the co-infection groups was significantly higher than that in the other groups(P < 0.05).2、Diversity study of Escherichia coli from broilers infected with immunosuppressive virusesTo better understand the diversity of serotype and drug resistance of E.coli from the broilers infected by immunosuppressive viruses. E.coli isolates derived from one-day-old broilers single-infected or co-infected with avian leukosis virus subgroup J(ALV-J) and reticuloendotheliosis virus(REV) were isolated, identified and used for drugs sensitivity experiment. Five red or(and) white clones were picked from the diseased organ. 516 E.coli isolates were isolated from 58 diseased chickens of two repeated experiments including 445 red colonies and 71 white colonies. The results showed that co-infection could infect more serious mortality and among these 516 tested E.coli colonies, 12 serotypes of O-antigen were identified. E.coli of different serotypes was even isolated from the same organ in the same bird. 17 groups of colonies(5 same O-serotype colonies isolated from the same organ in the same bird were identified as a group of colonies) were selected to drug susceptibility test for12 kinds of common antibiotics. The drug susceptibility test results showed that the minimum inhibitory concentration was from 0.05 mg/ml to 51.20 mg/ml in third group to colimycin and from 0.05 mg/ml to 51.20 mg/ml in the seventeenth group to amikacin. However, differences in the other groups were not significant.