Tick-borne encephalitis (TBE) is a

viral Viral means "relating to viruses" (small infectious agents). Viral may also refer to: Viral behavior, or virality Memetic behavior likened that of a virus, for example: * Viral marketing, the use of existing social networks to spread a marke ...

infectious disease An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dise ...

involving the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...

. The disease most often manifests as

meningitis Meningitis is acute or chronic inflammation of the protective membranes covering the brain and spinal cord, collectively called the meninges. The most common symptoms are fever, headache, and neck stiffness. Other symptoms include confusion or ...

encephalitis Encephalitis is inflammation of the brain. The severity can be variable with symptoms including reduction or alteration in consciousness, headache, fever, confusion, a stiff neck, and vomiting. Complications may include seizures, hallucinations, ...

or meningoencephalitis. Myelitis and spinal paralysis also occurs. In about one third of cases

sequela A sequela (, ; usually used in the plural, sequelae ) is a pathological condition resulting from a disease, injury, therapy, or other trauma. Derived from the Latin word, meaning “sequel”, it is used in the medical field to mean a complication ...

e, predominantly cognitive dysfunction, persists for a year or more. The number of reported cases has been increasing in most countries. TBE is posing a concerning health challenge to Europe, as the number of reported human cases of TBE in all endemic regions of Europe have increased by almost 400% within the last three decades. The tick-borne encephalitis virus is known to infect a range of hosts including ruminants,

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...

rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are na ...

s, carnivores,

horse The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million y ...

s, and humans. The disease can also be spread from animals to humans, with ruminants and dogs providing the principal source of infection for humans.Tickborne Encephalitis Virus
reviewed and published by WikiVet, accessed 12 October 2011.

Signs and symptoms

The disease is most often biphasic. After an incubation period of approximately one week (range: 4–28 days) from exposure (tick bite) non-specific symptoms occurs. These symptoms are fever, malaise, headache, nausea, vomiting and myalgias that persist for about 5 days. Then, after approximately one week without symptoms, some of the infected develop neurological symptoms, i.e. meningitis, encephalitis or meningoencephalitis. Myelitis also occurs with or without encephalitis.

Sequela A sequela (, ; usually used in the plural, sequelae ) is a pathological condition resulting from a disease, injury, therapy, or other trauma. Derived from the Latin word, meaning “sequel”, it is used in the medical field to mean a complication ...

e persists for a year or more in approximately one third of people who develop neurological disease. Most common long-term symptoms are headache, concentration difficulties, memory impairment and other symptoms of cognitive dysfunction. Mortality depends on the subtype of the virus. For the European subtype mortality rates are 0.5% to 2% for people who develop neurological disease. In dogs, the disease also manifests as a neurological disorder with signs varying from

tremor A tremor is an involuntary, somewhat rhythmic, muscle contraction and relaxation involving oscillations or twitching movements of one or more body parts. It is the most common of all involuntary movements and can affect the hands, arms, eyes, fa ...

s to

seizure An epileptic seizure, informally known as a seizure, is a period of symptoms due to abnormally excessive or synchronous neuronal activity in the brain. Outward effects vary from uncontrolled shaking movements involving much of the body with los ...

s and death. In ruminants, neurological disease is also present, and animals may refuse to eat, appear lethargic, and also develop respiratory signs.

Cause

TBE is caused by tick-borne encephalitis virus, a member of the genus ''

Flavivirus ''Flavivirus'' is a genus of positive-strand RNA viruses in the family ''Flaviviridae''. The genus includes the West Nile virus, dengue virus, tick-borne encephalitis virus, yellow fever virus, Zika virus and several other viruses which may caus ...

'' in the family Flaviviridae. It was first isolated in 1937. Three virus sub-types also exist: European or Western tick-borne encephalitis virus (transmitted by '' Ixodes ricinus''), Siberian tick-borne encephalitis virus (transmitted by '' I. persulcatus''), and Far-Eastern tick-borne encephalitis virus, formerly known as Russian spring summer encephalitis virus (transmitted by ''I. persulcatus''). The former Soviet Union conducted research on tick-borne diseases, including the TBE viruses.

Transmission

It is transmitted by the bite of several species of infected woodland

tick Ticks (order Ixodida) are parasitic arachnids that are part of the mite superorder Parasitiformes. Adult ticks are approximately 3 to 5 mm in length depending on age, sex, species, and "fullness". Ticks are external parasites, living by ...

s, including ''Ixodes scapularis'', '' I. ricinus'' and ''I. persulcatus'', or (rarely) through the non-pasteurized milk of infected cows.CDC Yellow Book
accessed 5 October 2013. Infection acquired through goat milk consumed as raw milk or raw cheese (Frischkäse) has been documented in 2016 and 2017 in the German state of Baden-Württemberg. None of the infected had neurological disease.

Diagnosis

Detection of specific IgM and IgG antibodies in patients sera combined with typical clinical signs, is the principal method for diagnosis. In more complicated situations, e.g. after vaccination, testing for presence of antibodies in

cerebrospinal fluid Cerebrospinal fluid (CSF) is a clear, colorless body fluid found within the tissue that surrounds the brain and spinal cord of all vertebrates. CSF is produced by specialised ependymal cells in the choroid plexus of the ventricles of the bra ...

may be necessary. It has been stated that

lumbar puncture Lumbar puncture (LP), also known as a spinal tap, is a medical procedure in which a needle is inserted into the spinal canal, most commonly to collect cerebrospinal fluid (CSF) for diagnostic testing. The main reason for a lumbar puncture is to ...

always should be performed when diagnosing TBE and that pleocytosis in cerebrospinal fluid should be added to the diagnostic criteria. PCR (polymerase chain reaction) method is rarely used, since TBE virus RNA is most often not present in patient sera or

at the time of neurological symptoms.

Prevention

Prevention includes non-specific (tick-bite prevention, tick checks) and specific prophylaxis in the form of a

vaccination Vaccination is the administration of a vaccine to help the immune system develop immunity from a disease. Vaccines contain a microorganism or virus in a weakened, live or killed state, or proteins or toxins from the organism. In stimulating ...

Tick-borne encephalitis vaccine Tick-borne encephalitis vaccine is a vaccine used to prevent tick-borne encephalitis (TBE). The disease is most common in Central and Eastern Europe, and Northern Asia. More than 87% of people who receive the vaccine develop immunity. It is not ...

s are very effective and available in many disease endemic areas and in travel clinics. Trade names are ''Encepur N'' and ''FSME-Immun CC''.

Treatment

There is no specific

antiviral Antiviral drugs are a class of medication used for treating viral infections. Most antivirals target specific viruses, while a broad-spectrum antiviral is effective against a wide range of viruses. Unlike most antibiotics, antiviral drugs do no ...

treatment for TBE. Symptomatic brain damage requires hospitalization and

supportive care Symptomatic treatment, supportive care, supportive therapy, or palliative treatment is any medical therapy of a disease that only affects its symptoms, not the underlying cause. It is usually aimed at reducing the signs and symptoms for the comfor ...

based on syndrome severity.

Anti-inflammatory drugs Non-steroidal anti-inflammatory drugs (NSAID) are members of a therapeutic drug class which reduces pain, decreases inflammation, decreases fever, and prevents blood clots. Side effects depend on the specific drug, its dose and duration of ...

, such as

corticosteroid Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex of vertebrates, as well as the synthetic analogues of these hormones. Two main classes of corticosteroids, glucocorticoids and mineralocorticoids, are involv ...

s, may be considered under specific circumstances for symptomatic relief.

Tracheal intubation Tracheal intubation, usually simply referred to as intubation, is the placement of a flexible plastic catheter, tube into the vertebrate trachea, trachea (windpipe) to maintain an open airway or to serve as a conduit through which to administer ce ...

and respiratory support may be necessary.

Epidemiology

As of 2011, the disease was most common in

Central Central is an adjective usually referring to being in the center of some place or (mathematical) object. Central may also refer to: Directions and generalised locations * Central Africa, a region in the centre of Africa continent, also known as ...

and

Eastern Europe Eastern Europe is a subregion of the Europe, European continent. As a largely ambiguous term, it has a wide range of geopolitical, geographical, ethnic, cultural, and socio-economic connotations. The vast majority of the region is covered by Russ ...

, and Northern

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an area ...

. About ten to twelve thousand cases are documented a year but the rates vary widely from one region to another. Most of the variation has been the result of variation in host population, particularly that of deer. In Austria, an extensive vaccination program since the 1970s reduced the incidence in 2013 by roughly 85%. In Germany, during the 2010s, there have been a minimum of 95 (2012) and a maximum of 584 cases (2018) of TBE (or FSME as it is known in German). More than half of the reported cases from 2019 had

or myelitis. The risk of infection was noted to be increasing with age, especially in people older than 40 years and it was greater in men than women. Most cases were acquired in Bavaria (46%) and Baden-Württemberg (37%), much less in Saxony, Hesse, Lower Saxony and other states. Altogether 164

Landkreis In all German states, except for the three city states, the primary administrative subdivision higher than a '' Gemeinde'' (municipality) is the (official term in all but two states) or (official term in the states of North Rhine-Westphalia ...

e are designated TBE-risk areas, including all of Baden-Württemberg except for the city of Heilbronn. In Sweden, most cases of TBE occur in a band running from Stockholm to the west, especially around lakes and the nearby region of the Baltic sea. It reflects the greater population involved in outdoor activities in these areas. Overall, for Europe, the estimated risk is roughly 1 case per 10,000 human-months of woodland activity. Although in some regions of Russia and Slovenia, the prevalence of cases can be as high as 70 cases per 100,000 people per year. Travelers to endemic regions do not often become cases, with only 5 cases reported among U.S. travelers returning from Eurasia between 2000 and 2011, a rate so low that as of 2016 the U.S.

Centers for Disease Control and Prevention The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georgi ...

recommended vaccination only for those who will be extensively exposed in high risk areas.

References

External links

Tickborne encephalitis
at

(CDC)
Factsheet
from Viral Special Pathogens Branch at the CDC {{DEFAULTSORT:Tick-Borne Encephalitis Tick-borne diseases Viral encephalitis Slow virus diseases Vaccine-preventable diseases