History and exam

Key diagnostic factors

common

presence of risk factors

Key risk factors include: history of recent tick bite (within past 4-28 days), summer months, occupational exposure, outdoors activities, or recent consumption of raw (unpasteurised) milk or dairy products.

fever

Occurs in 99% of patients.[13]

fatigue

Occurs in 63% of patients.[13]

general malaise

Occurs in 62% of patients.[13]

headache

Occurs in 54% of patients.[13]

body pains

Occurs in 54% of patients.[13]

nausea

Occurs in approximately 50% of patients.[13]

mild meningitis

Mild presentations of meningoencephalitis are more common in patients aged <50 years.[11]

severe encephalitis

Severe presentations of meningoencephalitis are more common in patients aged ≥50 years.[11]

altered mental state

Occurs in one third of patients.[13]

Other diagnostic factors

uncommon

cranial and spinal nerve palsies

Cranial and spinal nerve palsies occur in 3% to 13% of patients.[13] Cranial nerve involvement is mainly associated with ocular, facial, and pharyngeal motor function.[13]

vestibular/hearing defects

Vestibular and hearing defects are also encountered.[13]

seizures

Severe presentations of meningoencephalitis, such as seizures, are more common in patients aged ≥50 years.[11]

paresis

In about 5% to 10% of cases, monoparesis, paraparesis, and tetraparesis can develop, as well as paralysis of respiratory muscles, requiring ventilator support.[13]

arms, shoulders, and head muscles paralysis

Because of virus preference for the anterior horn of the cervical spinal cord, a flaccid poliomyelitis-like paralysis arises that, unlike poliomyelitis, usually affects the arms, shoulders, and levator muscles of the head.[13]

Risk factors

strong

history of recent tick bite

Tick-borne encephalitis (TBE) viruses are transmitted by tick vectors in disease-endemic areas, usually from the Ixodes genus of hard ticks.​[16] Tick bites, however, are often painless.[20] The tick bite is unnoticed in about one third of patients.[13] 

summer months

TBE occurs throughout the northern hemisphere, and mirrors the geographical distribution of the usual vector, Ixodes species ticks.[10]

In Europe, tick activity starts in spring when the temperature approaches 6ºC and usually persists until November when the temperature falls.[13]

TBE occurs focally throughout the northern hemisphere between June and October, with a peak in July.[14]​​

occupational exposure

Outdoor occupations such as forestry and military training increase the risk of TBE.[11]

outdoors activities

Most infections result from tick bites acquired in forested areas through activities such as camping, hiking, fishing, bicycling, and collecting mushrooms, berries, or flowers.[11]

recent consumption of raw (unpasteurised) milk or dairy products

TBEV infection may be acquired by consuming unpasteurised milk from infected animals.[2]​[15]​​

age ≥45 years

Most cases are reported in people aged 45-64 years.[14]​ The incidence and severity of disease are highest in people aged ≥50 years.[11]

weak

bioterrorism

The Far Eastern subtype and the Siberian subtype are classified as select agents in the US as both subtypes have the potential to pose a severe threat to both human and animal health, to plant health, or to animal and plant products.[23]​​

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