BACKGROUND:Tick-borne encephalitis virus (TBEV) is a pathogenic human flavivirus endemic in some parts of Europe and Asia. Commercial enzyme immunoassays (EIA) for the detection of IgG antibodies are often used in TBEV-seroprevalence studies, as well as for the confirmation of a successful vaccination against TBEV. However, the detection of TBEV-specific antibodies can be biased by the cross-reactivity between different flavivirus genera.OBJECTIVES:To compare different EIA test systems for the detection of TBEV-IgG antibodies.STUDY DESIGN:Six commercial EIA kits for the detection of TBEV-specific antibodies are compared, using serum panels (n=139) of subjects with a documented clinical history (109 sera from TBEV infected patients, 30 sera from people vaccinated against TBEV). For the analysis of possible cross-reactivities, 24 sera from yellow fever vaccinated people and 13 sera positive for Dengue virus-specific antibodies were also included.RESULTS:The sensitivity of the different TBEV test systems ranges from 73 to 99%. However, when testing the yellow fever and Dengue virus positive specimens, problems with the flavivirus cross- reactivity become obvious, resulting in specificities between 14 and 81%.CONCLUSIONS:This study shows the necessity of further improvement of the existing TBEV test systems regarding both sensitivity and specificity.

Monoclonal antibodies (MoAbs) were raised against the tick-borne encephalitis (TBE) virus, strain K23. The reactivities of 14 selected MoAbs were characterized by ELISA, Western blot analysis, haemagglutination inhibition, immunoprecipitation, in vivo protection and in vitro neutralization tests. All MoAbs reacted only with the glycoprotein E. The binding epitope of one MoAb could be delimited by a synthetic peptide to amino acids 306-339 representing one immunodominant loop structure of the glycoprotein E. The MoAbs exhibited individual reactivities against 13 different TBE virus isolates in ELISA and immunoblot test ranging from type-specific reactions to a broad reactivity with all isolates. Four MoAbs also showed a cross-reaction with other flaviviruses like West Nile virus and/or Yellow fever virus in immunoblot analysis. By competition ELISA the MoAbs could be divided into five different reaction patterns. Four MoAbs showed neutralizing activity with titers in the range 1:140 to 1:5,000 in an in vitro assay. These neutralizing activities could be confirmed by an in vivo mouse challenge model. The MoAbs are useful for diagnostic purposes and for differentiation of TBE virus strains and other flaviviruses.

The isolation of influenza virus envelope glycoproteins was achieved by one-step procedure consisting of treatment of purified virus with zwitterionic detergent and separation of viral constituents by sucrose density gradient centrifugation. Viral glycoproteins and proteins of outer membrane of N. meningitidis or B. burgdorferi formed complexes after removal of the detergent by dialysis. Complexing of viral glycoproteins and bacterial proteins was monitored by gel chromatography on Sepharose 6B, polyacrylamide gel electrophoresis and electron microscopy. It was demonstrated by immunoblot analysis, that virus-spirochete complexes elicited formation of antibodies in mice directed against osp A and osp B of spirochete, as well as against viral glycoproteins, respectively.

Serious infection due toBorrelia burgdorferi and the disseminated infection characteristic of the disease possess unique treatment problems. The wide and still increasing incidence of Lyme borreliosis as well as the problems in treatment call for effective prevention strategies by active immunization. Vaccination experiments were done to determine if active immunization of gerbils with recombinant OspA and pC protects against infection with strains ofB. burgdorferi. Gerbils were vaccinated with recombinant OspA and pC (20 kDa protein) and challenged four weeks later with a clone (derived fromB. burgdorferi strain PKo) which expresses an abundant amount of pC but only little OspA. Non-immunized gerbils challenged with the sameB. burgdorferi strain were used as controls. Both groups of immunized gerbils developed antibodies against the recombinant vaccines. The pC vaccinated group was protected against infection, whereas the OspA vaccinated group showed signs of infection. The non-vaccinated group developed generalised infection. These results show that pC should be considered as a further vaccine candidate and probably needs to be combined with OspA for an efficient vaccine againstB. burgdorferi.

A new, highly purified inactivated tick-borne encephalitis (TBE) vaccine (FSME-Vaccine Behring, BI 71.061) was recently registered in Germany. A multinational phase II study was performed in seven centres located in areas endemic for TBE. A total of 379 healthy adults were randomly allocated into three dosage groups (1.0, 1.5 and 2.0 μg antigen per dose, respectively) and into two immunization schedules [vaccination with one dose of 0.5 ml intramuscularly on days 0, 7 and 21 (abbreviated schedule), or on days 0, 28 and 300 (conventional schedule)]. Antibody response to vaccination was assayed by enzyme-linked immunosorbent assay (ELISA), haemagglutination inhibition test (HIT) and neutralization test (NT). Seroconversion rates in the different groups 28 days after one single dose were 75.3–83.5% in ELISA, 35.8–50.6% in HIT, and 100% in NT. All vaccinees showed seroconversion in all tests on day 42 in the conventional schedule and on day 35 in the abbreviated schedule, with the exception of one subject, who remained seronegative in HIT only. Geometric mean titres (GMT) of about 3000 in ELISA were achieved by two vaccinations in the conventional schedule and showed a booster increase to 5500–8000 GMT after revaccination on day 300. Overall frequency of adverse events (related and unrelated) was 37% (conventional schedule) and 46% (abbreviated schedule) after the first, 9% and 21% after the second, and 5% and 15% after the third vaccination, respectively. Generally, side effects were mild and transient, including mainly headache, fever, malaise and local irritation. Serious, vaccine-related side effects did not occur. It is concluded that the vaccine is immunogenic and well tolerated and that both immunization schedules can be recommended.

A highly purified, inactivated tick-borne encephalitis (TBE) virus particle vaccine has been developed. In this study we report on the efficacy of this new vaccine to protect against TBE virus isolates from different geographical areas of Europe and the Asian part of the USSR.

Humoral immunity against tick-borne encephalitis virus (TBEV) in patients with a well-documented history of naturally acquired tick-borne encephalitis (TBE) was compared with immunity resulting from vaccination in a carefully controlled immunization programme. The vaccination study was performed with a highly purified, inactivated virus particle vaccine and the immune response was followed by tracing the course of IgG antibody formation in an enzyme-linked immunosorbent assay and a neutralization assay. It was shown that this TBE vaccine induced a strong immune response. TBE IgG antibody titres measured after three vaccinations were of the same order of magnitude as those determined in patients recovered from manifest TBE.

A new vaccine against tick-borne encephalitis was investigated in 56 healthy volunteers randomized for five different doses of antigen in a comparative group trial. Good tolerability and high immunogenicity were found using three different antibody test systems. The dose response study revealed that there was a strong relationship between the amount of antigen administered and the antibody response over the range of 0.03–3.0 μg antigen per dose

A new tick-borne encephalitis (TBE) vaccine for human use has been developed. TBE virus (TBEV) was propagated in primary chick embryo cells, inactivated by formalin and purified by continuous-flow density gradient centrifugation. The TBE vaccine was tested for innocuity, immunogenicity and protective capacity in a series of laboratory tests. The results indicated that the vaccine is outstandingly well tolerated, highly immunogenic in various laboratory animals, and induces protective immunity in mice. These data suggest that this new vaccine should be studied in clinical trials.