Molecular and serological tools for clinical diagnostics of Lyme borreliosis - can the laboratory analysis be improved?
Sammanfattning: Lyme borreliosis (LB) is caused by spirochetes within the Borrelia burgdorferi sensu lato complex and is the most common tick-transmitted disease in the northern hemisphere. The transmission of the spirochetes to humans in Europe is done by the Ixodes ricinus ticks, which can also transmit the relapsing fever species Borrelia miyamotoi. LB may cause clinical manifestations in the skin, in the central nervous system, in joints, and in the heart. Diagnosis of LB is mainly based on the patient´s medical history, self-described symptoms, and clinical signs in combination with the detection of Borrelia-specific antibodies (serological methods). In some cases/issues, detection of Borrelia-specific deoxyribonucleic acid (molecular methods) may be used as a complement to serology. All diagnosed LB infections are treated with antibiotics to prevent disease progression, and most patients fully recover without further sequelae. The overall aims of this thesis were to evaluate molecular and serological tools for laboratory diagnosis of LB, with a special focus on Lyme neuroborreliosis (LNB), and to identify potential improvements.The results presented in this thesis showed that the immunoglobulin (Ig) G assays, currently in use in northern Europe for detection of antibodies in serum, had high diagnostic sensitivity (88 %) together with comparable results both between and within assays. For the IgM assays, the diagnostic sensitivity was lower (59 %) with more heterogeneous results. Small variations in diagnostic performance for IgM and IgG were mainly presented for samples within the borderline zone. These results support the theory that separate testing of IgM antibodies in serum has low diagnostic value. However, simultaneous detection in serum and cerebrospinal fluid (CSF) for both IgM and IgG antibodies was essential for the diagnosis of LNB, at least for certain assays.So far (to our knowledge), no systematic evaluation and optimisation of the pre-analytical handling of CSF samples before molecular testing has been performed. By use of the precipitate concentrated by moderate centrifugation, extraction of total nucleic acid followed by reversetranscription to complementary deoxyribonucleic acid, in combination with the absence of polymerase chain reaction (PCR) inhibitors, detection of Borrelia garinii, Borrelia afzelii, Borrelia burgdorferi sensu stricto, and B. miyamotoi was possible. These four species are all known to be pathogenic to humans. The results revealed a high analytical sensitivity and specificity for the optimised pre-analytical conditions. The thesis also presents results showing that the real-time PCR protocols currently used in Scandinavia have high analytical sensitivity, specificity, and concordance. This indicates that the low diagnostic sensitivity for detection of Borrelia in CSF was not a result of poorly designed and evaluated PCR protocols, but was possibly due to the low number of spirochetes in the samples. However, to further evaluate the diagnostic performance for detection of Borrelia in CSF by PCR, clinical samples need to be evaluated based on our new recommendations for the pre-analytical handling of CSF samples.In conclusion, this thesis presents results revealing that both molecular and serological tools for detection of Borrelia have, in general high sensitivity and specificity with results comparable between different protocols and different laboratories. It also presents recommendations for pre-analytical handling of CSF samples before PCR-analysis, and shows the benefits in diagnostic performance by simultaneous detection of IgM and IgG antibodies in serum and CSF for accurate diagnosis of LNB. Even though the techniques mentioned above have high analytical performance, the ability to discriminate an active infection from a previous one is limited and further studies need to be carried out. These studies need to focus on finding diagnostic tools that can help physicians to determine ongoing infection to ensure adequate treatment. It is also desirable to improve the standardisation of the diagnostic tools and to find methods that can discriminate between different Borrelia species.
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