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 occur. 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 has 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.

TBE virus infections are often asymptomatic, which means that the infected individual show no symptoms of disease. In clinical cases, 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 occur. 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. The 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.