Diagnosis of tick-borne encephalitis

The actual diagnosis of a tick-borne encephalitis (TBE) must be established in the laboratory because of the non-specific clinical features it presents. The method of choice is the demonstration of specific IgM- and IgG-serum antibodies by enzyme-linked immuno-sorbent assay (ELISA), since these antibodies are detectable in practically every case at the time of hospitalization. Early after onset of disease in the cerebrospinal fluid specific antibodies can only be found in 50% of the patients, but by the 10th day of illness they almost invariably become detectable. If an infection occurs after and despite the post-exposure administration of a specific immunoglobulin the seroconversion can be delayed and may cause diagnostic problems. Virusisolation from the blood, or the detection of specific nucleic acid in the blood or the cerebrospinal fluid by reverse-transcriptase polymerase chain reaction (RT-PCR) usually is only successful during the first viremic phase of the disease before seroconversion. In fatal cases, the virus can be isolated or detected by RT-PCR from the brain and other organs. For testing immunity after a TBE virus infection or after vaccination, most often the IgG ELISA is used. However, in cases of other flavivirus contacts (e.g. vaccinations against yellow fever or Japanese encephalitis; dengue virus infections), the performance of a neutralization assay is necessary for assessing immunity due to the interference of flavivirus cross-reactive antibodies in ELISA and hemagglutination inhibition (HI) test. (C) 2003 Elsevier Science Ltd. All rights reserved.