DIAGNOSIS
Diagnosis of chlamydial infections can be difficult; the clinical signs and gross pathological lesions are not sufficiently specific to allow diagnosis, and PCR, serology, antigen detection or demonstration of chlamydia are required for diagnosis.
Serology is based on enzyme-linked immunosorbent assay (ELISA), micro - immunofluorescence test and CFT used for antibody detection with variable specificity and sensitivity. Detection of chlamydial antigens in tissues of dead animals, oculonasal and cloacal swabs, and faeces can be performed using ELISA or immunofluorescence staining techniques. Direct microscopy can be useful as a screening test, in which detection of the typical intracytoplasmic inclusions in tissue cells and cells in exudative discharges can support suspicions of disease. Cytology is performed on stained smears, e.g. with Gimenez, Stamp or Macchiavello. PCR technology is improving detection sensitivity of the organism in clinical material (faeces and bronchial exudates) and more particularly in cases of subclinical infection, with results already indicating higher prevalences of infection that previously indicated with other diagnostic tests. PCR and microarray genotyping make species identification of chlamydiae a routine process. Extracellular culture has never been achieved; however, culture is possible in cell culture, with embryonated chicken eggs, but is difficult and requires biosafety level 3 laboratories. CFT serology has been used historically for general surveys on archived avian blood samples, including those from wild birds; however, the test has limitations, seen with non-specific reactions and the choice of a reliable cut-off value. Published references should describe these limitations (for example(4)). Detailed guidelines for the diagnosis of avian chlamydiosis are available in the World Organisation of Animal Health (OIE) Manual of Diagnostic Tests and Vaccines for Terrestrial Animalfιτ,.
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