Tick-borne encephalitis (TBE) is a viral infection thatcaused causesby minimalthe orthe notick-borne symptomsencephalitis invirus (TBEV) which belongs to the majorityFlavivirus genus. TBE is usually transmitted to humans through the bite of an infected tick. Although infection can occur through consumption of infected unpasteurised dairy products.

Infection with TBEV causes no symptoms or only mild symptoms in most people. In rare cases, theTBEV viruscauses canan attackacute infection of the central nervous system andleading to meningitis or encephalitis or other neurological syndromes. This can occasionally result in long-term neurological symptoms orand (veryin rarely)severe death.cases TBEdeath. 

A related virus, louping ill virus (LIV) is closely related to TBEV), and causes louping ill disease in sheep, although human infections can occur with a similar syndrome to infection with TBEV. Together TBEV and LIV belong to the tick-borne encephalitis complex.

TBEV is endemic in ticks and animals in rural and forested parts of Europe, Russia, China and Japan. In recent years, TBE has become an increasing public health concern due to the expansion of endemic areas. In the UK, a membersmall number of locally acquired cases have been reported since 2019.

There is no specific antiviral treatment for TBE. Cases with neurological symptoms require hospitalisation and supportive care.

Preventing tick bites is the genusmain Flavivirus.way to reduce the risk of infection. A vaccine against TBEV is available and is recommended for people travelling to areas where the virus is endemic and exposure risk is high.

Epidemiology

TBEV has 5a widespread geographic distribution across much of mainland Europe, with substantial increase in both case numbers and the extent of affected areas in the past 30 years. Areas of higher risk reflect the preferred habitat of infected ticks, which are mainly rural and forested environments.

The main subtypes,vectors for TBEV are Ixodes ricinus ticks which are widespread in the UK, and Ixodes persulcatus ticks which are not native to the UK but can be found in Europe and northern Asia, including China and Japan. The main reservoir hosts for TBEV are small mammals, particularly rodents (such as voles, mice) and insectivores (such as shrews). Other animals contribute indirectly to virus circulation by enabling tick multiplication, including wild and domestic mammals, such as hares, deer, wild boar, sheep, cattle and goats.

TBEV has 5 closely related:related subtypes:

• European,European subtype - transmitted by Ixodes ricinus ticks, and endemic in rural and forested areas of central, eastern and northern Europe

• Far-Eastern,Far-Eastern subtype - transmitted mainly by Ixodes persulcatus, andit is endemic in far-eastern Russia and in forested regions of China and Japan

• Siberian,Siberian subtype - transmitted by Ixodes persulcatus, andit is endemic in Uralsthe Ural region, SiberiaSiberia, and far-eastern Russia, and some areas in north-eastern Europe

• theBaikalian subtype -  a recently recognised Baikaliansubtype subtype, transmitted transmitted by Ixodes persulcatus,persulcatus and found in East Siberia

• theHimalayan subtype- a recently recognised Himalayansubtype subtype,, for which Marmota himalayana (Himalayan marmot) is the primary reservoir host, andidentified found on in the Qinghai-Tibet Plateau in China

The European subtype is generally associated with a milder disease.

Seedisease Ixodescompared ricinuswith distributionother map.TBEV subtypes.

UK epidemiology

SeeIn Ixodesthe persulcatusUK, distributionTBEV map.

Competent(European reservoirsubtype) hostswas offirst detected in ticks in 2019. To date, TBEV areinfected mainlyticks smallhave rodentsbeen (voles,detected mice)in Thetford Forest, the Hampshire-Dorset border and insectivoresparts (shrews).of Otherthe animalsNorth supportYorkshire virusMoors.

The circulationfirst indirectlyprobable byhuman enablingcase of locally acquired TBE was diagnosed in 2019 following a tick multiplication.bite Thesein includethe wildNew andForest. domesticAs mammals,of especiallyApril hares,2026, deer,there wildhave boar,been sheep,6 cattleUK acquired cases reported.

Figure 1. Map showing location of confirmed and goats.probable TBE cases in the UK

Map shows:

1. One confirmed TBE complex case acquired in the North Yorkshire Moors
2. One confirmed TBE complex case acquired around the Loch Earn area in Scotland
3. One probable case acquired in Dartmoor
4. Two probable complex cases acquired in Hampshire
5. One probable TBE complex case acquired in either the Peak District, South Yorkshire or Na h-Eileanan Siar (outer Hebrides)

Transmission

TBEV is is normally transmitted by the bite of an infected tick.

In humans,Following diseaseinfection humans are considered ‘dead end’ hosts as they do not develop sufficient levels of viraemia to enable onward transmission of virus to ticks. Infection can also beoccur acquiredthrough bythe consumption of unpasteurised milk or milkdairy products from infected animals, althoughparticularly cows, sheep or goats however this isroute veryof transmission is rare.

TBEV is not directly transmitted from person to person. ThereIsolated havecases been case reports of transmission through organ transplants,transplantation, blood transfusion, via the transplacental routetransmission and breastfeeding.through breastfeeding have been reported. Infection has also followedoccurred following laboratory sharps injuries.

Symptoms

The average incubation period of TBE is 7 days, but may be up to 28 days. The incubation period for foodborne infection is usually shorter, around 4 days.

Approximately two-thirds of human TBE virus infections are asymptomatic. In symptomatic cases, it is often biphasic, with an initial viraemic phase lasting approximately 5 days (range 2 to 10), and is associated with non-specific symptoms (fever, fatigue, headache, myalgia, nausea).

This phase is usually followed by an asymptomatic interval and apparent recovery, lasting 7 days (range 1 to 33). The second phase begins approximately 7 days after initial resolution of symptoms (range 1 to 33 days) and involves the central nervous system. Typical presentations are meningitis, meningoencephalitis, myelitis, paralysis, or radiculitis.

The European subtype is associated with milder disease, with 2020% to 30% of patients experiencing the second phase, severe neurological sequelae in up to 10% of patients, and an overall mortality of 0.50.5% to 2%. In children, the second phase of illness is usually limited to meningitis, while adults older than 40 years are at increased risk of developing encephalitis. There is a higher likelihood of long-lasting sequelae, and a higher mortality, in those over the age of 60 years, the immunocompromised, or those with significant co-morbidities.

Acute encephalitis of any cause is a notifiable disease and should be notified to the UK Health Security Agency (UKHSA) if suspected.

Anyone with flu-like symptoms following a tick bite should contact their GP ortheir GP or call NHS 111.

Laboratory diagnosis

TestingAcute isencephalitis doneof by the UKHSA Rare and imported pathogens laboratory (RIPL). If TBE is suspected, the referring clinician should contact a cliniciannotifiable atdisease RIPL to discuss the case to ensure that the correct samples are sent for testing.

TBEV is a notifiable organism,. andManaging youclinicians should notify yourtheir local health protection team ifwhen detected.

Risksthey forsuspect UKa travellersclinical case.

Diagnosis

IfIn you are travelling outside the UK, checkclinicians whetherwho yoususpect are visiting a placepatient wheremay have TBE, isor present.who TBEV-Eurhave isa endemicpatient inwith ruralundiagnosed andencephalitis forestedshould areasseek ofadvice central,from easternthe andUKHSA northernImported Europe.Fever TheService. incidence 

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Risk in the UK

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InClinicians Julyare 2019,encouraged ato Europeandiscuss visitorall becamesuspected illcases afterwith beingRIPL bittento byensure athat tickappropriate insamples theare Newsubmitted Forestand area.the Thiscorrect wasdiagnostic consideredpathway tois befollowed.

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Treatment

There Hampshire,is againno basedspecific ontreatment serologicalfor testing.TBE.

Prevention

InTick Septemberbite 2022,avoidance aand thirdregular case,checking confirmedfor positiveand byremoval polymeraseof chainticks reactionare (PCR),the wasmost diagnosedimportant inpreventive anmeasures individualfor people who isare likelyplanning to havevisit acquiredareas infectionat inhigh therisk Loch Earn area of Scotland.

Intick Octoberbites 2022,either a fourth case, also confirmed positive by PCR, was diagnosed in anthe individualUK whoor reportedabroad. recentThis exposureincludes tostaying tickson inpaths theand Northavoiding Yorkshirelong Moorsgrass inwhen England.

Towalking date,outdoors, allusing otherinsect casesrepellent, ofwearing TBEVlong infectionsleeved reportedshirts inand thetrousers UKand haveregularly beenchecking acquiredfor throughticks travelon toskin high-riskand areas abroad.clothing.

TheUKHSA riskhas fromproduced TBEVresources isto currentlysupport assessedawareness asraising veryinitiatives. lowA forvaccine theis generalavailable public, and low for high-riskpeople groupsvisiting (suchhigh asrisk thoseareas. living,Further workinginformation oron visiting affected areas).

Lyme disease remains the mostTBE commonlyvaccine acquiredcan tick-bornebe infectionfound acquired in thechapter UK31 andof itthe isGreen important to be tick aware when spending time outdoors.Book

Tick

Main resourcestick and surveillance

resources:

• Tick toolkitstoolkit and tick awareness materials

  Iinformation

• Tick onsurveillance howscheme
• NaTHNaC totick-borne takeencephalitis partfactsheet
• One inHealth thevector-borne tickdisease surveillance scheme

  For

• Ixodes furtherricinus information,distribution seemap
• Ixodes NaTHNaCpersulcatus factsheetdistribution map.