-We have amplified, cloned and sequenced (part of) the open reading frame of the S1 segment encoding the σ C protein of avian reoviruses isolated from chickens with different disease conditions in Germany and The Netherlands during 1980 up to 2000. These avian reoviruses were analysed phylogenetically and compared with sequences of avian reoviruses in the Genbank database. The avian reoviruses could be grouped in 5 different genotyping clusters and this classification was identical when the sequences were compared of the 5' end, the 3' end or the whole open reading frame of the σ C protein. Therefore sequencing of either part of the gene encoding the σ C protein seems to be reliable for classification. We were unable to identify a correlation between σ C sequences of the avian reoviruses and the disease condition they were isolated from. The sequences found in The Netherlands and in Germany are, like those in Taiwan, more dispersed than the known avian reovirus σ C sequences in the USA and Australia. We did not establish temporal or geographic differences in the avian reoviruses studied. avian reovirus / malabsorption syndrome / tenosynovitis / σ C gene / genotype

Five malabsorption syndrome (MAS) homogenates from The Netherlands and Germany were used to reproduce MAS in broilers. We studied the histopathology after inoculation of 1-day-old broiler chicks and the agents that might be involved. Generally, the MAS homogenates induced signs that differed in severity and pathobiology. We could distinguish and classify the inoculated groups best by histopathology: proventriculitis, lesions in the small intestines in combination with proventriculitis, or lesions of the small intestines only. Lesions in the small intestine had more impact on weight gain depression than lesions in the proventriculus. In three out of five inoculated groups, microscopic lesions of the pancreas were found. Reovirus was detected in the inoculated groups by virus isolation and seroconversion, and reoviral antigen was detected by immunohistochemistry of the small intestine. Also, enteroviruslike particles were detected in three of the five inoculated groups, although not in the most affected group. Additionally, bacteriophages and bacteria (hemolytic Escherichia coli, Pasteurella hemolytica, and Enterococcus durans) were isolated from inoculated chicks. The role these agents play in pathogenesis of MAS is still unsolved.

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SUMMARYUsing immunohistochemical methods, we studied the nephropathogenicity of the infectious bronchitis virus (IBV)-strain V1648-and the leukocyte phenorypes in the pathological lesions in the kidneys and the trachea formed after inoculation with this virus strain. One-day-old WLA chickens were intravenously inoculated, and after 5, 7 and 11 days their kidneys, trachea and lungs were removed. Monoclonal antibodies were used to detect viral antigen, and lymphoid and non-lymphoid cell populations. In serial sections, the detection of the viral antigen was correlated to the phenotypes of the cells. At days 5 and 7 after inoculation, viral antigen was detected in the epithelium and the interstitium of the kidney tubuli and in the epithelium of the trachea. The infiltrated cells in these tissues were mainly of the T cell phenotype. The cellular immune reaction was correlated with the detection of viral antigen.

-The enteropathogenicity of avian reoviruses (ARVs), isolated from chickens affected with malabsorption syndrome (MAS) from The Netherlands and Germany was studied. In the first trial seven different ARVs isolated from MAS cases were inoculated in 1-day-old specific pathogenic free (SPF) white leghorns. The pathogenicity was compared with 2 ARVs isolated from cases of tenosynovitis, namely reference strain S1133 and a Dutch strain. Although a difference in the severity of the clinical disease was observed, all reoviruses could induce vacuolar degeneration and sloughing of the epithelium of the small intestine at day 2 post inoculation (PI) till day 7 PI. Two Dutch and one German ARV derived from MAS causing the most severe intestinal lesions at day 2 PI, were further studied in the second trial using SPF broilers. These reoviruses did not cause weight gain depression in the broilers although lesions in the small intestine were present from day 1 up to day 4 PI and were more severe than in the white leghorn chickens. In one of the inoculated groups apical denuded villi were already present at day 1 PI. At day 7 PI the small intestine of the infected broilers appeared to be normal. Reovirus antigen was detected in the cytoplasm of the enterocytes at the tip and middle section of the affected villi both in layers and in broilers. To study the role of intestinal CD4 + and CD8 + T-cells and macrophages/monocytes in the pathogenesis of ARV, the numbers of these cells of the jejunal villi of one infected and the control broiler groups were compared. CD4 + T-cells were detected in low numbers and only in the infected broiler group at day 14 PI. The numbers of CD8 + T-cells and macrophages/monocytes were significantly higher in the infected broiler group than in the control broiler group at day 7 and 14 PI and at day 7 PI respectively. Our study indicates that the reovirus alone cannot induce intestinal lesions as found in MAS chickens. Moreover, CD8 + T-cells may play a major role in the pathogenesis and or reovirus clearance in the small intestine. malabsorption syndrome / runting-stunting syndrome / reovirus / enteropathogenicity / chicken