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Serological assessment of chlamydial infection in the koala by a slide EIA technique

Ueno, H, Mizuno, S, Takashima, I, Osawa, R, Blanshard, W, Timms, P, White, N & Hashimoto, N 1991, Australian Veterinary Journal, vol. 68, no. 12, pp. 393-396

A slide enzyme immunosorbent assay (EIA) that can reliably detect Chlamydia psittaci antibody in koala blood serum is described in this study, presenting a rapid, simple and reliable alternative to existing methods.

  To trial the new method, a strain of C. psittaci antigen obtained from a conjunctival swab of a koala exhibiting symptoms of severe conjunctivitis was firstly propagated in vitro. Several blood samples were then collected from both free-ranging and captive koalas either from the cephalic vein, ear-prick method, or both. Cephalic vein blood samples were either separated using a centrifuge or supernatant extracted using a sampling paper technique, whereas ear-prick blood samples were only subject to the sampling paper technique. For the slide EIA procedure, koala sera were diluted and applied to antigen slides. The results of the slide EIA method were compared to those of a conventional complement fixation (CF) test. The slide EIA was found to be equally as sensitive as the CF test for detecting C. psittaci antibody in koala cephalic vein blood samples, with a 97% agreement rate between the two tests using both the serum separation and sampling paper techniques. When an ovine strain of C. psittaci antigen was tested rather than the koala strain, the slide EIA test was consistently more reliable at detecting C. psittaci antibody than the CF test with sensitivity rates of 100% and 43% respectively. This result may indicate that the slide EIA technique could effectively detect a wider range of chlamydial antibodies than the CF test and perhaps even detect infection earlier than was previously possible. A comparison of the results of the slide EIA using ear-prick blood samples and cephalic vein sera revealed a 96% agreement rate. This high similarity suggests that the blood sampling paper method would be a reliable and practical substitute for conventional serum separation when the equipment required for the latter method is unavailable, such as in the field.

  Chlamydial infections are a major threat to koalas, and the disease is thought to be prevalent in most free-ranging populations. In efforts to combat the disease, it is important that practitioners are equipped with a practical and reliable method for its detection. Chlamydial isolation in cell culture is a reliable method but is not feasible without specialised laboratory skills and facilities. An alternative method, the CF test, is more commonly used but its sensitivity compared to that of the cell culture method is questionable. The creators of the slide EIA method put forward in this study suggest that it suitably overcomes the pitfalls of previous methods by providing accurate results and requiring only simple equipment. The new procedure was employed for the assessment of animals in Lone Pine Koala Sanctuary, and may also be suitable for the monitoring infection in free-ranging populations.

 

Summarised by Joanna Horsfall

 

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