Tick-borne encephalitis

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.