Cross-European laboratory evaluation of commercial and in-house real-time PCR assays for the detection of Chlamydia abortus in small ruminants

Chlamydia abortus is a bacterial pathogen that causes enzootic abortion of ewes (EAE), a disease of sheep and goats with potential risks to human health. Accurate detection is essential for disease management and prevention. While serological tests have been widely used for herd screening, they are lacking in terms of sensitivity and specificity. PCR methods, particularly real-time PCR, are now preferred due to their improved sensitivity and accuracy for confirmation of clinical cases and for use in routine surveillance. This study aimed to compare and evaluate the analytical parameters and diagnostic performance of two commercial PCR tests and four in-house PCR methods for their suitability for diagnosing EAE. Two of the in-house methods are based on the ompA gene, which is specifically used to detect C. abortus in ruminants. The other two tests target different genetic markers, that also allow the detection of avian C. abortus strains. The study found that all PCR tests had a similar analytical sensitivity and were effective in identifying C. abortus in clinical samples, such as placentas, vaginal swabs and fetal organs especially in animals showing symptoms. However, detection in asymptomatic carriers was more difficult. One of the ompA-based assays showed superior diagnostic accuracy, particularly compared to the commercial kits, with a diagnostic sensitivity of 98.0 % and a diagnostic specificity of 96.6 % and is thus the one recommended for routine testing. The study also concluded that the interpretation criteria of the commercial kits should be reviewed to improve their reliability.