Comparison of Two Commercial Tick-Borne Encephalitis Virus IgG Enzyme-Linked Immunosorbent Assays

Abstract

Despite the availability of protective vaccines, tick-borne encephalitis virus (TBEV) infections have been increasingly reported to the European Centre for Disease Prevention and Control in the past 2 decades. Since the diagnosis of TBEV exposure relies on serological testing, we compared two commercial enzyme-linked immunosorbent assays (ELISAs), i.e., Immunozym FSME IgG assay (ELISA-1) and Euroimmun FSME Vienna IgG assay (ELISA-2). Both assays use whole TBEV antigens, but they differ in viral strains (Neudoerfl for ELISA-1 and K23 for ELISA-2) and cutoff values. In testing of samples from 398 healthy blood donors, ELISA-1 showed higher reactivity levels than ELISA-2 (P < 0.001), suggesting different assay properties. This finding was supported by Bland-Altman analysis of the optical density at 450 nm (OD 450 ) (mean bias, ؉0.32 [95% limits of agreement, ؊0.31 to ؉0.95]) and persisted after transformation into Vienna units. Concordant results were observed for 276 sera (69%) (44 positive and 232 negative results). Discordant results were observed for 122 sera (31%); 15 were fully discordant, all being ELISA-1 positive and ELISA-2 negative, and 107 were partially discordant (101 being ELISA-1 indeterminate and ELISA-2 negative and 6 having positive or indeterminate reactivity in both ELISAs). Neutralization testing at a 1:10 dilution yielded positive results for 33 of 44 concordant positive sera, 1 of 15 fully discordant sera, and 1 of 33 partially discordant sera. Indirect immunofluorescence testing revealed high antibody titers of >100 for yellow fever virus in 18 cases and for dengue virus in one case, suggesting that cross-reactivity contributed to the ELISA-1 results. We conclude that (i) cross-reactivity among flaviviruses remains a limitation of TBEV serological testing, (ii) ELISA-2 revealed reasonable sensitivity and specificity for anti-TBEV IgG population screening of human sera, and (iii) neutralization testing is most specific and should be reserved for selective questions. Despite the availability of protective vaccines, tick-borne encephalitis (TBE) has been increasingly reported in Europe over the past 2 decades (1). According to a recent analysis by the European Centre for Disease Prevention and Control (ECDC), 29,381 cases of TBE have been diagnosed in 16 countries of the European Union (EU)/European Free Trade Association (EFTA) since the year 2000. The annual rates range from 2,000 to 3,500 cases per year, showing a net increase despite a remarkable and as yet unexplained 3-year peak periodicity. Climate changes, with milder winters and earlier and prolonged summer seasons, and increasing numbers of small rodent and larger wild and domestic animal hosts, such as deer, sheep, and goats, are thought to contribute to expanding areas in which tick-borne encephalitis virus (TBEV)-infected ticks are endemic, which facilitates human exposure during occupational and leisure activities outdoors (2-4). The notable exception to this European trend is Austria, where TBEV vaccination has been effectively ...

EAN consensus review on prevention, diagnosis and management of tick‐borne encephalitis

“…A confirmed diagnosis of TBE is established by the detection of specific IgM and IgG serum antibodies, usually by highly sensitive and specific enzyme-linked immunosorbent assay (ELISA) [65,114,136]. Generally, comparison of commercial serological diagnostic methods has shown good sensitivity and good agreement between different methods but lack of specificity demonstrating a limitation of cross-reactivity amongst flaviviruses [137,138]. Earlier studies on quality control assessment for serological diagnosis of TBE in different laboratories revealed correct results for at least 90% of samples by 33 of 40 laboratories for IgM, and in 16 of 42 laboratories for IgG, demonstrating the need for standardized quality measures [139,140].…”

“…To avoid a false positive diagnosis, in potential cases for cross-reactivity with other flaviviruses, a confirmatory neutralization assay (the most specific test available) is recommended [13,137,138]. Rarely IgM antibody quantification may be needed, to avoid interference factors in the serodiagnosis of TBE [102].…”

Exposure of cattle to tick-borne encephalitis virus in the historical endemic zone in north-eastern France

“…This suggests that cattle may have only been weakly exposed to USUV in our study. However, we cannot exclude that USUV or other circulating flaviviruses were responsible of some positive cross-reactions with Immunozym cELISA results as in healthy blood donors in Switzerland [42]. Although ID Screen® cELISA has been recommended as a pan-flavivirus diagnostic tool in horses [34] and is used to detect TBEV in goats and sheep [43], it was not as effective as expected to detect TBEV antibodies in cattle sera.…”

Tick-borne zoonotic flaviviruses and Borrelia infections in wildlife hosts: What have field studies contributed?

“…Both of these reports may result from cross-reactivity of antibodies against other flaviviruses. To address this question, some commercial TBEV ELISA have been compared for their reliability according to the TBEV-strain and for the at-risk cross-reactivity [ 87 ]. Because TBEV and LIV as well as Turkish Sheep Encephalomyelitis virus (TSEV) and Spanish Sheep Encephalomyelitis virus (SSEV) belong to the TBEV-serocomplex [ 65 ], they can particularly easily be mistaken in serology.…”