Chlamydial infection may be diagnosed to a large extent on the characteristic clinical signs, specifically a marked, often persistent conjunctivitis ( see table ). Another aid in differentiation between chlamydial and viral infection of the respiratory tract is that chlamydial infection may respond to certain antibiotics.
Diagnosis may be confirmed in untreated cases by the following approaches:
- A Giemsa-stained conjunctival scraping or smear may be directly examined for the presence of inclusion bodies. These are most numerous in the first 7 days of clinical disease, and are only occasionally seen up to 14 days. However, the results can be difficult to interpret.
- More reliably, some specialist laboratories offer attempted isolation of organism in cell culture from a firmly taken conjunctival swab. Chlamydia are intracellular parasites, and it is important that epithelial cells be present in the sample. Specialised transport media are required, and either rapid transport to the laboratory or -700C storage before collection. Either immunofluorescence or histochemical stains can then be used to confirm the identify of the intracytoplasmic inclusions in the cell cultures.
- Several commercial kits have been developed for use in diagnosis of human chlamydial infections and can be used for diagnosis in cats. These kits use a genus-specific monoclonal or polyclonal antibody which is either used in an immunofluorescent test on conjunctival smears, or has been incorporated into an ELISA. These techniques are not as sensitive as culture in the later stages of the disease, but have the advantage that both viable and non-viable organisms can be detected.
- In unvaccinated cats a positive serologic response or demonstration of a significant rise in antibody titre may also be helpful in diagnosis. The indirect immunofluorescent test is generally more reliable in detecting antibody than the older complement fixation test.
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