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In order to evaluate the serological response to agents associated to chronic respiratory syndrome in poultry, 120 White Leghorn replacement layers, having received all the vaccines of the immunization program currently applied in Cuba, were selected and sampled monthly from the 12th to the 50th week of age. The samples were assayed for antibodies against Mycoplasma gallisepticum (by fast serum plate agglutination), Ornithobacterium rhinotracheale and Avian Infectious Bronchitis Virus (by ELISA), and Newcastle Disease Virus (by hemagglutination inhibition assay, HIA); comparing the proportion of birds positive to Mycoplasma gallisepticum, Ornithobacterium rhinotracheale, or with HIA titers higher than 1/8, and performing an analysis of variance for the geometric means of the antibody titers against the Avian Infectious Bronchitis Virus at p < 0.05 for statistical significance, as implemented in the Comprop-1 and Statgraphics Plus 5.1 statistical software packages. The results corroborated the presence of M. gallisepticum and provided the first evidence of positive reactions to O. rhinotracheale in laying hens with chronic respiratory syndrome. The serological kinetics of the bird population vaccinated against avian infectious bronchitis evidenced a second seroconversion event, probably due to the circulation of this infectious agent. No serological responses against Newcastle Disease Virus were detected. Further studies for the isolation and characterization of different O. rhinotracheale serovars from laying hens with chronic respiratory syndrome are required.

In order to dissect the histopathological changes produced by the infection of avian infectious bronchitis virus in previously vaccinated egg-laying hens from a poultry farming unit, 35 White Leghorn egg-laying hens that had been in production for 9 to 10 months (twenty seven of which had clinical symptoms corresponding to respiratory disease and eight apparently healthy individuals) were selected for further study. After clinical examination and necropsy, they were classified into apparently healthy, mild, moderate or severe according to the severity of the clinical-pathological process. Samples were taken from paranasal sinuses, trachea and lungs for histopathological study, and trachea-lung pools were prepared from four individuals for virus isolation and molecular biology assays. The presence of mucus was evidenced with Schiff’™s non-enzymatic histochemical staining, and histomorphometric analyses were used to estimate the number of glands in the tracheal mucosa. The proportions of histopathological lesions were compared, using one-way Anova to determine gland loss at the tracheae with a significance level of p < 0.05 in both cases. Histopathological analysis of the epithelia of paranasal sinuses, trachea and bronchia revealed the presence of epithelial erosion, mucous exudate and hyperplasia of mucosa-associated lymphoid tissue. Glandular cysts were observed at the paranasal sinuses, and epithelial metaplasia was detected in the trachea. It was possible to isolate and identify infectious bronchitis coronavirus from the original samples and from samples passaged in chicken embryos.