Tick-borne encephalitis

thumb|Sucking female tick in electron microscope

Tick-borne encephalitis (TBE) is a disease caused by the tick-borne meningoencephalitis virus, which belongs to the arboviruses. The disease can lead to meningitis, meningoencephalitis and severe encephalomyelitis. The course is variable - from abortive forms (with few symptoms) to a typically two-phase course with central nervous system involvement. The clinical picture is based on febrile illness, headache and neurological symptoms. There is no specific antiviral therapy, the treatment is only symptomatic. TBE mortality is low, but permanent neurological sequelae are relatively common. It is possible to vaccinate againstTBE.

Tick-borne meningoencephalitis virus is one of the most common causes of aseptic neuroinfections in the Czech Republic. The clinical picture of meningitis prevails in children, up to 2/3 of children show cognitive deficits after having KME and have memory problems.

Epidemiology
Tick-borne encephalitis is a local seasonal neuroinfection.

The reported incidence of tick-borne encephalitis in the Czech Republic in the years 2000–2009 is 500–1000 cases per year, ie 5-10 patients per 100,000 population per year. It has been known in the Czech Republic only since 1945 and its occurrence is most frequent in the Vltava, Berounka and Sázava river basins, in Central and Southern Bohemia, most often from April to October.
 * Originator : arbovirus (is arthropod-borne virus, enveloped RNA virus ) of the family Flaviviridae.
 * Infection reservoir : small rodents and larger forest animals, sheep, goats, but also beasts.
 * Transmission (vector): by sucking blood of infected nymphs or adult ticks ( Ixodes ricinus );
 * the virus is in the saliva of ticks, so a short suction time is enough to transmit;
 * the virus survives in the salivary glands of the tick, in the tick there is also a transovarian transmission of the virus;
 * tick penetration in endemic areas is up to 1%;
 * rarely alimentary - by consuming unpasteurized milk from infected goats and sheep.
 * Incubation period : 3-28 days.

Clinical symptoms and course
The incubation period of the disease is 7–14 days, with an extreme range of 3–30 days. Most diseases are inapparent. After 1-3 weeks  incubation, a two-phase course is usually typical:
 * Phase 1 ("flu") –
 * - viremia with headache and muscle pain, fever, fatigue, the condition will improve in a few days. An apparent recovery in the form of an afebrile period (2-7 days) follows
 * an asymptomatic period that lasts 1–20 days.
 * Phase 2 – meningeal symptoms : headache, photophobia, encephalomyelitic symptoms: alterations of consciousness ( sleepiness to coma ), cranial nerve disorders, bulbar syndrome, weak limb paresis, high fever, sleep disturbance, vomiting, tremors.

Based on the predominant disability, we can divide encephalitis into the form:


 * inapparent (specific antibody production only);
 * abortifacient (nonspecific symptoms similar to influenza illness );
 * meningeal ( viral meningitis);
 * encephalic (gray and white brain disease with neurological symptoms);
 * encephalomyelitic (involvement of gray, white matter and anterior horns);weak paresis, especially of the brachial plexus, may occur in pacentas, as segments C5–7 are most often affected by the process.


 * bulbocervical (involvement of the elongated spinal cord ), bulbocervical forms can also lead to the failure of vital centers and thus to death.

Diagnosis

 * positive meningeal symptoms in people living in the endemic area;
 * a history of a typical two-phase course;
 * tick bite data - indicates only a part of patients with KME;
 * detection of specific antibodies from serum - ELISA with detection of early IgM antibodies, IgG class antibodies are formed very quickly, for which their avidity can be determined;
 * other serological methods : specific virus neutralization test, rise of specific antibodies ( KFR, HIT );
 * cerebrospinal fluid examination: aseptic inflammation with a leukocyte count ranging from 100-200 leukocytes / μl, slightly elevated protein levels;
 * EEG in the acute phase: diffuse pathological recording with a predominance of slow waves.

Treatment
So far it is only symptomatic ( analgesics, antiemetics , antipyretics ), rest regime is especially important. Relieving lumbar puncture can be performed (tens to hundreds of lymphocytes in the CSF, slightly higher protein). We treat paresis by administering '''vit. B and rehabilitation'''. Anti-edematous treatment (mannitol) and corticoids also have a positive effect. It is recommended to avoid the sun, prolonged television and higher mental strain.

Prevention
Vaccination with an inactivated virus vaccine (FSME-IMMUN (Baxter) since 1976 and Encepur (Novartis) since 1991). The basic vaccination schedule consists of 3 doses. Vaccines are well tolerated, the most common adverse reactions being a temperature in the range of 38.0-39.0 ° C (20% of children; most often in the age group of 1-3 years; most in the period from February to March, ie in the period of frequent respiratory infections), injection site pain and, rarely, muscle weakness. The World Health Organization recommends vaccination against tick-borne encephalitis to all people living in the endemic area, including children.

The disease prevention includes regimens including appropriate clothing covering the entire body, the use of repellents, early removal of the tick and disinfection of the injection site.

Drinking of pasteurized milk is also a prevention (it is also spread through the milk of infected animals, including cow's milk.  ).

Prognosis and consequences
Heavier forms require convalescence lasting weeks to months. Residues persist (in 10% of patients)  in the form of peripheral weak paresis, memory, concentration and sleep disorders.

Related articles

 * Lyme disease
 * Encephalitis
 * Lumbar puncture
 * Neuroinfections
 * Tick-borne encephalitis viruses