Comparison of Four Commercial IgG-Enzyme-Linked Immunosorbent Assays for the Detection of Tick-Borne Encephalitis Virus Antibodies

Can the booster interval for the tick-borne encephalitis (TBE) vaccine 'FSME-IMMUN' be prolonged? - A systematic review

Tick-borne encephalitis (TBE) vaccines are effective and well tolerated. However, their acceptance and use by the public in endemic areas are suboptimal. To some extent this is due to the complicated dosing schedule requiring frequent boosters at variable intervals that even change with age. Simplification of the dosing schedule has failed so far as it is debated if the persistence of TBE virus (TBEV) antibodies is the only relevant factor for protection or if immune memory plays a decisive role as well. The objective here is to present the available evidence to determine the need for boosters and their interval after a primary series of three doses of FSME-IMMUN. A systematic literature review was conducted with a focus on serology, particularly seropersistence, immune memory, effectiveness, and vaccine breakthroughs (VB) of FSME-IMMUN. While after a 3-dose primary series seropositivity persisted for more than 10 years in >90% of younger subjects, it dropped to 37.5% in those 60 years or older. In contrast, field effectiveness of FSME-IMMUN remains high in irregularly vaccinated subjects and thus does not correlate well with the percentage of subjects achieving an arbitrarily defined threshold of persisting antibodies. FSME-IMMUN booster doses led to increases in antibody responses within 7 days. VB are rare and remain poorly understood. VB did not increase, and vaccine effectiveness did not significantly decrease with time since completion of the primary vaccination series or with the time since administration of the last vaccine dose. For all these reasons, data identified from this systematic review suggest that seropersistence alone does not explain the high effectiveness of FSME-IMMUN irrespective of the time since the last vaccine dose was administered. Induction of immunological memory characterized by a rapid and sustained secondary immune response is proving to be an alternative mechanism of action for protection against TBE. In this context Switzerland and Finland have adopted a longer booster interval (i.e., 10 years) following the three-dose primary immunization schedule without any evidence of harm at a population level. Longer booster intervals will likely drive up vaccine uptake. There is a lack of data to base an interval recommendation beyond 10 years.

Analysis of effectivity of the tickborne encephalitis virus detection methods in ixodid ticks

Tick-borne encephalitis (TBE) is transmissible viral disease widely common in temperate zone of Eurasia. ELISA and PCR are used for express identification of the vector's infection, but the results of the two methods often do not agree. Aim of the work is comparative analysis for TBE virus of Ixodid ticks from nature using complex of methods, including ELISA, PCR, and isolation of the virus in laboratory mice. 18608 Ixodid ticks were collected during 2013-2019 in TBE natural foci of the Baikal Region. The ticks suspensions were examined individually, using ELISA (n=17610) and PCR (n=2999). Suckling mice were inoculated with the suspensions positive in the both tests. The TBEV antigen was found in 1.2 % of ticks in average. All ticks positive in ELISA were examined in PCR (Group 1). Randomly selected part of negative-ELISA samples were examined in PCR too (Group 2). The PCR results were positive in 68.9±3.13 % of the Group 1, with average Ct index 24.6±0.38. Positive results of PCR in Group 2 accounted for just 2.7±0.31 % with average Ct index 31.0±0.70. The average Ct margin of the Groups 1 and 2 is statistically significant (p < 0.001; df = 118). Isolation of strains was significantly more successful in Group 1 (21.7±2.77 %), than in Group 2 (8.2±5.26 %; p < 0.05; df = 50). ELISA is more useful for examining large amounts of ticks. To get a more complex picture about epidemically dangerous part of the vectors in TBE natural foci, the results of the two express-methods is better to sum. The isolation of the virus is useful to carry out of the samples positive in ELISA and PCR concurrently.

Low Virus-Specific IgG Antibodies in Adverse Clinical Course and Outcome of Tick-Borne Encephalitis

Tick-borne encephalitis (TBE) is associated with a range of disease severity. The reasons for this heterogeneity are not clear. Levels of serum IgG antibodies to TBE virus (TBEV) were determined in 691 adult patients during the meningoencephalitic phase of TBE and correlated with detailed clinical and laboratory parameters during acute illness and with the presence of post-encephalitic syndrome (PES) 2–7 years after TBE. Specific IgG antibody levels ranged from below cut-off value (in 32/691 patients, 4.6%), to 896 U/mL (median = 37.3 U/mL). Patients with meningoencephalomyelitis were more often seronegative (24.3%; 9/37) than those with meningoencephalitis (4.7%; 20/428) or meningitis (1.3%; 3/226). Moreover, patients with antibody levels below cut-off had longer hospitalization (13 versus 8 days); more often required intensive care unit treatment (22% versus 8%) and artificial ventilation (71% versus 21%); and had a higher fatality rate (3/32; 9.4% versus 1/659; 0.2%) than seropositive patients. These results were confirmed when antibody levels, rather than cut-off values, were correlated with clinical parameters including the likelihood to develop PES. Low serum IgG antibody responses against TBEV at the onset of neurologic involvement are associated with a more difficult clinical course and unfavorable long-term outcome of TBE, providing a diagnostic and clinical challenge for physicians.

Multi-laboratory evaluation of ReaScan TBE IgM rapid test, 2016 to 2017

Background

Tick-borne encephalitis (TBE) is a potentially severe neurological disease caused by TBE virus (TBEV). In Europe and Asia, TBEV infection has become a growing public health concern and requires fast and specific detection.

Aim

In this observational study, we evaluated a rapid TBE IgM test, ReaScan TBE, for usage in a clinical laboratory setting.

Methods

Patient sera found negative or positive for TBEV by serological and/or molecular methods in diagnostic laboratories of five European countries endemic for TBEV (Estonia, Finland, Slovenia, the Netherlands and Sweden) were used to assess the sensitivity and specificity of the test. The patients’ diagnoses were based on other commercial or quality assured in-house assays, i.e. each laboratory’s conventional routine methods. For specificity analysis, serum samples from patients with infections known to cause problems in serology were employed. These samples tested positive for e.g. Epstein–Barr virus, cytomegalovirus and Anaplasma phagocytophilum, or for flaviviruses other than TBEV, i.e. dengue, Japanese encephalitis, West Nile and Zika viruses. Samples from individuals vaccinated against flaviviruses other than TBEV were also included. Altogether, 172 serum samples from patients with acute TBE and 306 TBE IgM negative samples were analysed.

Results

Compared with each laboratory’s conventional methods, the tested assay had similar sensitivity and specificity (99.4% and 97.7%, respectively). Samples containing potentially interfering antibodies did not cause specificity problems.

Conclusion

Regarding diagnosis of acute TBEV infections, ReaScan TBE offers rapid and convenient complementary IgM detection. If used as a stand-alone, it can provide preliminary results in a laboratory or point of care setting.

Comparative specificity and sensitivity of NS1-based serological assays for the detection of flavivirus immune response

Flaviviruses are relevant animal and human pathogens of increasing importance worldwide. The similarities of the initial clinical symptoms and the serological cross-reactivity of viral structural antigens make a laboratory diagnosis of flavivirus infection problematic. The main aim of the present study was the comparative specificity and sensitivity analysis of the non-structural protein NS1 as an antigen to detect flavivirus antibodies in sera from exposed individuals. A strategy for the purification of native recombinant non-structural protein 1 of representative flaviviruses including tick-borne encephalitis, West Nile, Zika and dengue virus was developed. The immunological properties of the purified antigens were analyzed using sera of immunized mice and of infected individuals in comparison with standard commercial assays. Recombinant NS1 protein was confirmed as a valuable option for the detection of flavivirus antibodies with reduced cross-reactivity and high sensitivity offering additional advantages for the detection of vaccine breakthrough cases.