Page 188 - TBE_Book_V2_2019

Chapter 10: Diagnosis

Direct detection of TBEV blood samples taken during the febrile phase
of the disease. Virus isolation is also used to
infection isolate TBEV strains from other biological
material (e.g., ticks, rodents, etc.) for use in
Virus isolation subsequent genetic and phenotypic character-
ization.
The isolation of TBEV was the first diagnostic
technique established for the confirmation of PCR
clinically suspicious CNS infections such as
TBE. In the past, virus isolation from blood and The current technology of choice for the
brain samples was performed in newborn detection of TBEV is PCR, and there are
mice, with many of the ‘old’ TBEV strains (e.g., several formats available. The earliest PCR-
Scharl, Absettarov, Sofjin, KEM II, Alsace, based method for detecting TBEV infection
7–9
Schaffhausen, etc.) isolated by intracerebral was nested RT-PCR, but a number of real-
inoculation of patient material or tick suspen- time RT-PCR assays for the detection of viral
sions. Cell culture was subsequently ribonucleic acid (RNA) in various clinical and
introduced and there are now a number of biological samples have also been described.
10
immortalized cell lines that can be used to PCR-based methods have no clear role in the
isolate TBEV from patient material. The most diagnosis of TBEV infection during the phase
frequently used cell lines are currently PS cells involving CNS symptoms because viral RNA
(porcine fetal kidney cells), Vero cells (green cannot usually be detected in blood or CSF
monkey fetal kidney cells), BHK-21 (baby samples during this phase of the disease.
4,8
hamster kidney cells), and A549 cells (human However, TBEV can be detected in blood
lung adenocarcinoma cells), although other samples during the first febrile phase of TBE as
lineages such as human neuroblastoma cells well as in brain tissue (if available) during the
may also be used. phase involving CNS symptoms. The RT-PCR
format is therefore a valuable diagnostic tool
Virus can be detected in an infected when there is a need to confirm an infection
individual’s blood during the first febrile phase with TBEV as the cause of a febrile illness
of the disease and can be detected pre-
following a tick bite, or when confirmation of a
dominantly in brain tissue during the second TBEV infection is sought in fatal cases. A
4
phase involving neurologic symptoms. The
recent Swedish study reported that TBEV RNA
cerebrospinal fluid (CSF) does not usually could also be detected by RT-PCR in urine
contain viable virus and should therefore only samples from patients for up to 19 days after
be used for virus isolation under special 11
the start of neurologic symptoms. Another
circumstances. No systematic studies on the application of RT-PCR in this setting is the
shedding of viable TBEV in the urine of
diagnosis of potential TBEV infections in
patients infected with TBEV are available to immunosuppressed patients unable to
date, but shedding in an immunocompro- develop antibodies to the virus. In these cases,
mised patient was observed to last for at least TBEV RNA may be detectable within blood and
5
56 days and intermittent shedding in urine CSF samples over a longer period of time
was observed for a period of more than 700 compared with immunocompetent patients.
6
days in experimentally infected monkeys.
Detectable TBEV was reported to be shed over
a period of at least 56 days in 1 immuno-
Virus isolation is no longer routinely used for 5
compromised patient.
diagnosis of a TBE infection but is still needed
to identify the subtype of TBEV present in
brain tissue samples from fatal cases or in

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