IBDV Gm 11 (Simbios eleven-molecular group) has been detected since 1997 in many farms of commercial broilers and layers causing high mortality (2 to 15%) and severe macro and microscopic damage in cloacal bursae, spleen, thymus, kidney and liver. Five serial passages of 2050/97-Gm 11 IBDV sample by CAM route in SPF chicken's embryonated eggs did not elicit increased embryo mortality. High mortality (100%) of 21 day-old SPF leghorn chickens and severe bursal and splenic lesions were seen from 24 up to 48 hours after eye-drop inoculation of 2050/97 strain (50 mL of 10-2 dilution of 10% bursae homogenate). Mortality was not detected when vaccinated SPF and broiler chickens were inoculated. One dead bird was found among ten challenged unvaccinated broilers. Variations in the intensity of cloacal bursae injury and spleen response were found between unvaccinated and vaccinated broiler chickens. IBDV antibodies were detected by ELISA test in almost all vaccinated SPF chickens before challenge while low number of commercial vaccinated and unvaccinated broilers were serologically positive (0 to 3 birds in 18). Increasing IBDV antibody titers were detected after challenge with 2050/97 strain and highest GMTs were found in broilers. It was concluded that 2050/97 strain is a highly virulent IBDV and SPF leghorn chickens immunized with BV8 intermediate vaccine strain were resistant to the challenge. Increasing susceptibility was found from experimental groups of unvaccinated broilers to vaccinated broilers and to unvaccinated SPF birds. It is discussed that passive immunity was involved in the rate of protection of challenged unvaccinated broiler and in the immune response impairment after vaccination of broilers chicks. The use of a constant virus suspension with known potency to challenge the experimental birds was suitable to evaluate vaccination efficacy. Evaluation of bursal and splenic responses at early and delayed time after challenge were useful to estimate vaccination efficacy and field interactions

Duodenum swabs were harvested from 80 broilers in 15 flocks of 8 broiler farms and were submitted to bacteriological evaluation. Five broiler breeders were sampled to obtain comparative data. Macro and microscopic lesions in the gut and the liver were evaluated in all birds submitted to swab harvesting and also broilers of two slaughter plants. Semiquantitative bacterial examination in duodenum swabs demonstrated higher microorganism growth in blood agar than in MacConkey medium. Staphylococcus sp, Enterococcus sp and Escherichia coli were found in some broiler flocks. An increased cellularity of the muscular mucosae of duodenum villi and/or the presence of some gametocytes or schizonts of coccidia were found in the lesioned gut in addition to high bacterial growth in blood agar. In some flocks, enlarged yellowish livers with vacuolated hepatocytes and/or increased reticuloendothelial response were seen in some birds. Liver and gut samples were collected in two slaughter plants in order to establish a pattern of response in broilers after withdrawal of growth promoters. Livers with macroscopic lesions presented microscopic lesions in the parenchyma such as increased leukocyte response in the sinusoidal space, vacuolar degeneration of hepatocytes or focal necrosis in the perilobular region, increased size or number of lymphoid nests in the perilobular region, the perivascular space and surrounding the biliary duct and increased extramedular granulocytopoiesis. Duodenum with hyperemic patches showed increased cellular response in the muscular mucosa of villi. These observations support the concept that semi-quantitative bacteriology and liver lesion evaluation could be used as a model to study gut bacterial imbalance in chickens