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Chapter 5: TBE in adults

at risk for TBE; however, the individual risk Epidemiological data from different European
depends on age, sex, occupation, leisure countries demonstrate that the incidence of
activity profile, and the local environmental TBE is higher in elderly people than in younger
presence of TBEV. Within the European Union age groups. In some countries (e.g., Germany,
(EU), TBE became a notifiable disease in 2012, Austria, Sweden, Lithuania) more than 50% of
and in 2014, 2,057 cases were reported to the TBE patients are ≥50 years of age. Long-term
European Centers for Disease Control and data (1993– 2008) from a single center in
Prevention (ECDC), 1,986 with a confirmed Białystok/Poland showed that among 710
TBEV infection based on ECDC diagnostic hospitalized patients with TBE, 235 patients
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criteria (0.42 cases per 100,000 population). (33%) were ≥50 years old. The clinical
The highest rates were documented in the manifestation of TBE depends on the virulence
Baltic states and TBE was predominantly of the pathogen and individual factors of the
reported in males ≥45 years of age. The host. The most important host risk factors are
majority of cases occurred in males in all age age, comorbidities, and notably immune-
groups, based on aggregated data from 2000– suppression. In detail, the latter encompass
2010 (n=22,378); however, in Lithuania, autoimmune diseases such as rheumatoid
Latvia, and Estonia in the ≥60 years group, arthritis, psoriasis, vasculitis, encephalo-
female cases predominated. The ECDC report myelitis disseminata, solid organ recipients, or
showed that most TBE cases were reported to oncological diseases requiring treatment with
public health authorities between June and biologicals, steroids, chemotherapeutic
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October. agents, or other immunomodulating sub-
stances. The case fatality rate for TBE is

exceedingly high in these patient groups. A
Predisposition factors and risk recently published cluster of TBEV in the organ
transplant recipients underscores the role of
factors host immune suppression and fatal out-
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comes.
Risk factors – age, comorbidities
Another factor that may result in a more
The personal risk for TBE in non-immune severe clinical picture of TBE is the relatively
persons depends on the probability of rare occurrence of coinfection with other tick-
exposure to TBEV. Exposure is usually the borne pathogens like Borrelia burgdorferi,
result of close contact with the environment Anaplasma phagocytopilum, Rickettsia spp.
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in which ticks are found. Forest workers, or Listeria monocytogenes. According to Pikelj
professional hunters, and landscape gardeners et al., other predictors for severe courses of
are examples for occupational groups with a TBE infection are early alteration of
relatively high work-related risk of acquiring a consciousness (Glasgow Coma Scale [GCS]
TBE infection. score <7), development of limb paralysis
together with respiratory insufficiency within
However, the most endangered groups for 24–48 hours from the beginning of the second
severe clinical manifestation are elderly phase of the disease, and pleocytosis >300
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people, with studies showing that TBE tends cells. According to Mickiene et al., a
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to be more severe in the elderly. This may be monophasic course of the disease is also a
due to their social habits and leisure activities, predictive factor. Late onset of specific anti-
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e.g., collecting mushrooms, hiking, or other TBEV IgM antibodies in cerebrospinal fluid
activities in the forests, that lead to a higher (CSF) is linked with the severity of acute
probability of exposure to ticks and therefore encephalitis symptoms. Thus, it can be
for TBEV infection.

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