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|Infected countries/areas in Eurasia|
Tick-borne encephalitis (TBE) is a viral infectious disease involving the central nervous system. The disease most often manifests as meningitis, encephalitis or meningoencephalitis. Myelitis and spinal paralysis also occurs. In about one third of cases sequelae, predominantly cognitive dysfunction, persist 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, birds, rodents, carnivores, horses, and humans. The disease can also be spread from animals to humans, with ruminants and dogs providing the principal source of infection for humans.
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.
Sequelae persist 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 tremors to seizures and death.
In ruminants, neurological disease is also present, and animals may refuse to eat, appear lethargic, and also develop respiratory signs.
TBE is caused by tick-borne encephalitis virus, a member of the genus Flavivirus in the family Flaviviridae. It was first isolated in 1937. Three virus sub-types also exist:
The former Soviet Union conducted research on tick-borne diseases, including the TBE viruses.
It is transmitted by the bite of several species of infected woodland ticks, including Ixodes scapularis, I. ricinus and I. persulcatus,or (rarely) through the non-pasteurized milk of infected cows.
Infection acquired through goat milk consumed as raw milk or fresh cheese (Frischkäse) has been documented in 2016 and 2017 in the German state of Baden-Württemberg. None of the infected had neurological disease.
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 may be necessary.It has been stated that lumbar puncture 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 cerebrospinal fluid at the time of neurological symptoms.
Prevention includes non-specific (tick-bite prevention) and specific prophylaxis in the form of a vaccination. Tick checks, while useful for preventing some other tick-borne diseases such as Lyme borreliosis, would not be expected to be effective in the prevention of tick-borne encephalitis as the virus is transmitted within minutes of attachment by the tick.
Tick-borne encephalitis vaccines are very effective and available in many disease endemic areas and in travel clinics.Trade names are Encepur N and FSME-Immun CC.
There is no specific antiviral treatment for TBE. Symptomatic brain damage requires hospitalization and supportive care based on syndrome severity. Anti-inflammatory drugs, such as corticosteroids, may be considered under specific circumstances for symptomatic relief. Tracheal intubation and respiratory support may be necessary.
As of 2011, the disease was most common in Central and Eastern Europe, and Northern Asia. 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 meningitis, encephalitis 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 Landkreise 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 8 cases reported among U.S. travelers returning from Eurasia between 2000 and 2017, a rate so low that as of 2020 the U.S. Centers for Disease Control and Prevention recommended vaccination only for those who will be extensively exposed in high risk areas.
West Nile fever is an infection by the West Nile virus, which is typically spread by mosquitoes. In about 80% of infections people have few or no symptoms. About 20% of people develop a fever, headache, vomiting, or a rash. In less than 1% of people, encephalitis or meningitis occurs, with associated neck stiffness, confusion, or seizures. Recovery may take weeks to months. The risk of death among those in whom the nervous system is affected is about 10 percent.
Lyme disease, also known as Lyme borreliosis, is a vector-borne disease caused by Borrelia bacteria, which are spread by ticks in the genus Ixodes. The most common sign of infection is an expanding red rash, known as erythema migrans (EM), which appears at the site of the tick bite about a week afterwards. The rash is typically neither itchy nor painful. Approximately 70–80% of infected people develop a rash. Early diagnosis can be difficult. Other early symptoms may include fever, headaches and tiredness. If untreated, symptoms may include loss of the ability to move one or both sides of the face, joint pains, severe headaches with neck stiffness or heart palpitations. Months to years later, repeated episodes of joint pain and swelling may occur. Occasionally, shooting pains or tingling in the arms and legs may develop. Despite appropriate treatment, about 10 to 20% of those affected develop joint pains, memory problems, and tiredness for at least six months.
Arbovirus is an informal name for any virus that is transmitted by arthropod vectors. The term arbovirus is a portmanteau word. Tibovirus is sometimes used to more specifically describe viruses transmitted by ticks, a superorder within the arthropods. Arboviruses can affect both animals and plants. In humans, symptoms of arbovirus infection generally occur 3–15 days after exposure to the virus and last three or four days. The most common clinical features of infection are fever, headache, and malaise, but encephalitis and viral hemorrhagic fever may also occur.
Tick-borne diseases, which afflict humans and other animals, are caused by infectious agents transmitted by tick bites. They are caused by infection with a variety of pathogens, including rickettsia and other types of bacteria, viruses, and protozoa. The economic impact of tick-borne diseases is considered to be substantial in humans, and tick-borne diseases are estimated to affect ~80 % of cattle worldwide.
Japanese encephalitis (JE) is an infection of the brain caused by the Japanese encephalitis virus (JEV). While most infections result in little or no symptoms, occasional inflammation of the brain occurs. In these cases, symptoms may include headache, vomiting, fever, confusion and seizures. This occurs about 5 to 15 days after infection.
Tick-borne encephalitis virus (TBEV) is a positive-strand RNA virus associated with tick-borne encephalitis in the genus Flavivirus.
Viral encephalitis is inflammation of the brain parenchyma, called encephalitis, by a virus. The different forms of viral encephalitis are called viral encephalitides. It is the most common type of encephalitis and often occurs with viral meningitis. Encephalitic viruses first cause infection and replicate outside of the central nervous system (CNS), most reaching the CNS through the circulatory system and a minority from nerve endings toward the CNS. Once in the brain, the virus and the host's inflammatory response disrupt neural function, leading to illness and complications, many of which frequently are neurological in nature, such as impaired motor skills and altered behavior.
Alkhurma virus (ALKV) is a zoonotic virus of the Flaviviridae virus family. ALKV causes Alkhurma hemorrhagic fever (AHF), or alternatively termed as Alkhurma hemorrhagic fever virus, and is mainly based in Saudi Arabia.
Powassan virus (POWV) is a Flavivirus transmitted by ticks, found in North America and in the Russian Far East. It is named after the town of Powassan, Ontario, where it was identified in a young boy who eventually died from it. It can cause encephalitis, an infection of the brain. No approved vaccine or antiviral drug exists. Prevention of tick bites is the best precaution.
Ixodes ricinus, the castor bean tick, is a chiefly European species of hard-bodied tick. It may reach a length of 11 mm (0.43 in) when engorged with a blood meal, and can transmit both bacterial and viral pathogens such as the causative agents of Lyme disease and tick-borne encephalitis.
Human granulocytic anaplasmosis (HGA) is a tick-borne, infectious disease caused by Anaplasma phagocytophilum, an obligate intracellular bacterium that is typically transmitted to humans by ticks of the Ixodes ricinus species complex, including Ixodes scapularis and Ixodes pacificus in North America. These ticks also transmit Lyme disease and other tick-borne diseases.
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 useful following the bite of an infected tick. It is given by injection into a muscle.
Mosquito-borne diseases or mosquito-borne illnesses are diseases caused by bacteria, viruses or parasites transmitted by mosquitoes. Nearly 700 million people get a mosquito-borne illness each year resulting in over 725,000 deaths.
Ticks are insects known for attaching to and sucking blood from land-dwelling animals. Ticks fall under the category of 'arthropod', and while they are often thought of in the context of disease transmission, they are also known to cause direct harm to hosts through bites, toxin release, and infestation. Infestation can cause symptoms ranging from mild to severe and may even cause death. Hosts can include any number of vertebrates, though humans and livestock are more likely to be the interest of researchers.
Borrelia miyamotoi is a bacterium of the spirochete phylum in the genus Borrelia. A zoonotic organism, B. miyamotoi can infect humans through the bite of several species of hard-shell Ixodes ticks, the same kind of ticks that spread B. burgdorferi, the causative bacterium of Lyme disease. Ixodes ticks are also the primary vector in the spread of babesiosis and anaplasmosis.
Kemerovo tickborne viral fever is an aparalytic febrile illness accompanied by meningism following tick-bite. The causative agent is a zoonotic Orbivirus first described in 1963 in western Siberia by Mikhail Chumakov and coworkers. The virus has some 23 serotypes, and can occur in coinfections with other Orbiviruses and tick-transmitted encephalitis viruses, complicating the course of illness. Rodents and birds are the primary vertebrate hosts of the virus; Ixodes persulcatus ticks are a vector of the virus. Kemerovo and related viruses may be translocated distances in the environment by migratory birds.
Ixodes persulcatus, the taiga tick, is a species of hard-bodied tick distributed from Europe through central and northern Asia to the People’s Republic of China and Japan. The sexual dimorphism of the species is marked, the male being much smaller than the female. Hosts include wild and domestic ungulates, man, dog, rabbit, and other small mammals, including the dormouse, Amur hedgehog, and occasionally birds.
Patricia (Pat) Anne Nuttall, OBE is a British virologist and acarologist known for her research on tick-borne diseases. Her discoveries include the fact that pathogens can be transmitted between vectors feeding on a host without being detectable in the host's blood. She is also a science administrator who served as the director of the Natural Environment Research Council (NERC) Centre for Ecology & Hydrology (2001–11). As of 2015, she is professor of arbovirology in the Department of Zoology of the University of Oxford.
Tibovirus is a term often used to describe viruses that are transmitted by tick vectors. The word tibovirus is an acronym. This falls within the superorder arthropod thus tibovirus is classified under Arthropod Borne virus (Arborvirus). For a person to acquire infection the tick must bite and feed for a sufficient period of time. The tiboviruses that affect humans are limited to within 3 families: Flaviviridae, Reoviridae, and Bunyaviridae.
Eyach virus (EYAV) is a viral infection in the Reoviridae family transmitted by a tick vector. It has been isolated from Ixodes ricinus and I. ventalloi ticks in Europe.