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Comparison of antigen detection and quantitative PCR in the detection of chlamydial infection in koalas (Phascolarctos cinereus)

Hanger, J, Loader, J, Wan, C, Beagley, KW, Timms, P & Polkinghorne, A 2013, The Veterinary Journal, vol. 195, no. 1, pp. 391-393.

Although an antigen detection method is less sensitive than quantitative polymerase chain reaction (qPCR) in the detection of Chlamydia pecorum infection in koalas, the former technique is suitable for rapidly diagnosing active chlamydial infections.

  The Clearview (CLV) enzyme immunoassay (EIA) is an antigen detection method that is commonly used to diagnose chlamydial infection in animals. The CLV EIA detects chlamydial antigens by using an antibody that targets the Chlamydiaceae-family-specific lipopolysaccharide. The purpose of this study was to compare the effectiveness of the CLV EIA in diagnosing C. pecorum infection in koalas to C. pecorum-specific qPCR, which is considered to be the more sensitive method. Swabs were taken from the conjunctival sac, nasal cavity and urogenital tract of 36 naturally infected koalas. Of 138 swabs taken, 81 tested positive for C. pecorum infection using the qPCR method, whereas only 35 of these 81 were C. pecorum-positive according to the CLV EIA. The level of agreement between the methods was therefore low at only 43.2%. Agreement between the two methods was lowest for nasal cavity swabs, possibly due to a lower load of C. pecorum at these, compared to other, sites. Conversely, agreement was highest for swabs collected from the urogenital tract where C. pecorum load was typically highest. The detection limit of the CLV EIA was approximately 384 C. pecorum cells / µL of swab material. Out of 57 C. pecorum-negative swabs, four false positives were detected by the CLV EIA. These may have been the result of the detection of DNA of other Chlamydia species, such as C. pneumoniae. The grade of the CLV signal (e.g. weakly positive, strongly positive) was strongly correlated with C. pecorum infectious load, thus making this technique potentially suitable for estimating chlamydial infection load where C. pecorum copies exceed the detection limit.

  A variety of techniques are used by researchers to diagnose chlamydial disease; however, different techniques are suited to different conditions. For instance, the qPCR technique is the ‘gold standard’ in chlamydial infection detection given its high sensitivity, but is not suitable when rapid diagnosis is required or in field conditions. Antigen detection methods, on the other hand, are suitable for rapid, in-field diagnoses, but are not reliable for detecting subclinical or low load infections. Based on the results of this study, the authors suggest that despite its poorer reliability than qPCR, the practicality of the CLV EIA makes it valuable as an adjunct clinical test for diagnosing chlamydial infection in koalas.

 

Summarised by Joanna Horsfall

 

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