Page 192 - TBE_Book_V2_2019

Chapter 10: Diagnosis

Figure 3: Calculation of IgM index when there needs to be a reliable
demonstration of immunity: only the
Titer TBE-lgM (CSF) Total lgG (CSF) detection of neutralizing antibodies allows a
lgM index > statement on the protection of a vaccinee
Titer TBE-lgM (SER) Total lgG (SER) against TBE.

ELISA

The ELISA format is the most commonly used
Figure 4: Calculation of intrathecal 19,20
test for detecting antibodies against TBEV.
antibody production The ELISA is usually conducted in a
standardized format and can be automated.
OD TBE-lgG (CSF) The various formats of anti-TBEV ELISAs on the
market use different antigens, such as
OD TBE-lgG (SER) European subtype strains (e.g., Hypr, K23,
lgG index > 2 Neudoerfl, K 1074) or Far Eastern subtype
Total lgG (CSF)
strains (e.g., Moscow B-4). The antigens used
Total lgG (SER) in the assays are whole-cell lysates or purified
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extracts derived from whole-cell lysates. The
results obtained from different ELISAs are not
OD TBE-lgG (CSF) comparable due to the different amounts of
antigen used. In general, ELISAs exhibit high
OD TBE-lgG (SER)
lgG index > 2 levels of sensitivity but only moderate
specificity due to cross-reactivity with
Albumin (CSF)
antibodies against dengue virus (caused by
Albumin (SER) infections) or yellow fever virus (caused by
vaccinations) and other flaviviruses.
The various formats of ELISA can distinguish
50%’ (TCID50) test. The TCID50 test involves a
defined number of infectious or lethal doses between different antibody isotypes, although
undergoing neutralization by varying concen- only IgM and IgG are usually relevant for a
diagnosis of TBEV infection (IgA does not play
trations of the serum being tested. The
any role in diagnosis but may be detectable in
dilution at which 50% of the original quantity
serum and CSF). IgM antibodies are usually
of virus is neutralized is termed the TCID50
titer and is usually calculated using the already present at the onset of clinical CNS
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formula of Reed and Muench. disease, or at least a few days after onset of
neurologic symptoms, and can be detected for
Neutralizing antibodies usually occur about 2 about 6 weeks after the onset of CNS
weeks after vaccination or infection. They are symptoms. A μ-capture ELISA has the highest
thought to be the most specific antibodies specificity for IgM testing. When using the 2-
produced by the host, and with the lowest layer ELISA format, IgG has to be removed
cross-reactivity to other flaviviruses. There- before testing in order to avoid false-negative
fore, one scenario that indicates the use of an results. Diagnostic tests for anti-TBEV IgM are
NT is when it is necessary to distinguish usually more specific than IgG tests with
between specific anti-TBEV antibodies and regard to cross-reactivity with other
antibodies against other flavivirus types. A flaviviruses (the author’s personal observa-
second scenario in which an NT is useful is tion).

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