Introduction:
Tick-borne encephalitis is an acute viral disease caused by the viruses of the family Flaviviridae.
These viruses are endemic to forested areas. The disease is more prevalent in Europe and North Asia. One of the viruses found in European countries is central European encephalitis (CCE), and the other one is more common in Asian parts of the former soviet union called Russian spring-summer encephalitis (RSSE). They are transmitted by ticks and infect humans, small mammals, and to a lesser extent, birds. The disease is characterized by sudden fever, headache, nausea, vomiting, and body pain. In addition, severe back pain is often associated with flaccid paralysis of the shoulder girdle and focal epilepsy. Hence, active immunization is the most crucial measure against the tick-borne encephalitis virus vaccine.
What Kind of Disease Is Tick-Borne Encephalitis?
Tick-borne encephalitis is an arthropod-transmitted viral disease caused by tick bites. The disease is endemic to most European and Russian countries, including China. The condition has been known by many names, such as central European encephalitis (CCE) and Russian spring-summer encephalitis (RSSE). The viruses of the family Flaviviridae cause it. Flavivirus is a large group of enveloped viruses responsible for several diseases, including Japanese encephalitis, yellow fever, dengue fever, and tick-borne encephalitis.
The virus particles are nearly spherical in shape. The diameter is around 40 to 50 nanometers. The genome consists of single-stranded ribonucleic acid. The envelope glycoprotein induces haemagglutination inhibition antibodies. This is the most essential antigen for protecting against diseases. The central European form (CCE) has a longer duration. It comes with a cephalic fever. The initial phase is not associated with disease of the central nervous system. It is only characterized by meningoencephalitis. The second phase infects the central nervous system leading to neurological outcomes, referred to as tick-borne encephalitis.
How Is Tick-Borne Encephalitis Virus Transmitted?
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Tick-borne encephalitis virus is mainly transmitted to humans and animals by tick bites.
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Alimentary transmission occurs after the consumption of dairy products or raw milk of viremic cows, goats, or sheep.
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Other reasons contributing to its transmission are a complex interplay of various biotic and abiotic factors and socio-economic and anthropogenic factors.
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In addition to this, migratory birds may contribute to an expanded occurrence.
In general, tick-borne encephalitis has become an international health concern.
What Are the Symptoms of Tick-Borne Encephalitis Infection?
Most cases of tick-borne encephalitis infection remain asymptomatic. However, the patient might have a monophasic or biphasic fever when symptoms come up. The incubation period ranges from two to twenty-eight days. Age, immune status, and virulence may affect the severity of the disease. The disease progresses with non-specific symptoms such as fatigue, headache, nausea, vomiting, and fever. The initial phase lasts for one to eight days. After an asymptomatic phase of one to twenty days, some people may develop a second phase that involves the central nervous system resulting in meningitis, encephalitis, and myelitis. Additionally, the development of permanent neurological issues has also been reported.
How Is Tick-Borne Encephalitis Virus Diagnosed?
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During the initial phase, the viral ribonucleic acid is present in blood and can be detected by reverse transcriptase-polymerase chain reaction, commonly known as RT-PCR. However, the initial phase might be asymptomatic in some, and patients are generally administered to the hospital after the appearance of neurological symptoms. By this time, ribonucleic acid is no longer present in the blood. Thus, reverse transcriptase-polymerase chain reaction (RT-PCR) plays little role in diagnosis.
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Therefore, diagnosing tick-borne encephalitis infection mainly relies on antibody testing. Tick-borne encephalitis virus-specific immunoglobulin (Ig) M and G are tested by enzyme-linked immunoassay (ELISA) and are highly specific in serum and cerebrospinal fluid. Therefore, the infection is mainly confirmed serologically.
Why Has the Incidence of Tick-Borne Encephalitis Increased?
The incidence of encephalitis has increased due to the expansion of the virus and its vectors. Since better antiviral treatments are lacking thus, vaccination against the virus is an essential measure. However, the coverage is relatively low, and immunogenicity is minimal, which may result in vaccine failure. The vaccine should induce both cellular and humoral immunity for robust protection against infection and the development of tick-borne encephalitis. Let us read in more detail about the tick-borne encephalitis virus vaccine.
Tick-Borne Encephalitis Virus Vaccine:
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The first vaccine against tick-borne encephalitis was prepared in 1941 in the brains of mice.
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Twenty years later, the vaccine was derived from cell culture and used for active human immunization.
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Later, an inactivated vaccine was developed, which was the most immunogenic.
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The efficacy of vaccines is relatively high, and many people develop immunity when they receive the vaccine. However, it is not helpful after the bite of an infected tick.
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The vaccine is recommended for all people living in high-risk areas where the disease is most prevalent.
Schedule:
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The vaccine can be used in children one to three years old and is safe during pregnancy.
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Three doses of vaccine are recommended.
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An additional dose every three to five years is recommended.
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The gap between the first and second doses should be one to three months and between the final dose is five to twelve months.
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However, immunization does not provide complete protection. Vaccination failures can occur in patients with incomplete or irregular vaccinations. All age groups can be affected, but the breakthrough infection is more common in people older than fifty.
Conclusion:
Tick-borne encephalitis vaccine prevents tick-borne encephalitis, a disease most common in Europe and North Asia. Two main variants are usually found named central European encephalitis (CCE) and other as Russian spring-summer encephalitis (RSSE). Currently, no licensed antiviral drugs against tick-borne encephalitis virus are available, and treatment is mainly supportive. Therefore, besides preventive measures like wearing protective clothing and avoiding the consumption of unpasteurized milk, active immunization is of utmost importance in fighting against the tick-borne encephalitis virus vaccine.Three doses of vaccines are recommended, and children above one to three years of age can receive the vaccination. It is safe in pregnancy. However, if not urgent, one can postpone the vaccination till delivery. Serious side effects are very uncommon and are the same as other vaccines. Minor side effects include fever, redness, and pain at the injection site.
