Tick -Borne Encephalitis (TBE)
Tick-borne encephalitis (or tick-borne meningoencephalitis or Tick-bite Encephalitis) is an acute viral disease of the central nervous system.
It is caused by an arborvirus belonging to the Flavivirus genus (very similar to the viruses responsible for yellow fever and dengue), which is spread to humans by the bite of ticks of the genus Ixodes.
Transmission to humans occurs mainly through the bite of infected ticks but also through the consumption of infected dairy products. The distribution and seasonal incidence of TBE reflect the ticks’ biology (maximum activity in spring and summer). Larvae, nymphs and adult ticks can spread the infection. The tick uses saliva to anesthetise the site of the bite, which can therefore go unnoticed. Inter-human transmission, although not documented, cannot be excluded (e.g. through transfusions).
Symptoms and complications
The disease can affect both adults and children, with very variable manifestations. Incubation is from 4 to 28 days (on average about 8 days after the bite).
In 70% of cases, the infection is asymptomatic or manifests with few relevant symptoms. In the remaining 30%, 3-28 days following the tick bite, there is a first phase with flu-like symptoms (high fever, strong headache, sore throat, fatigue, muscle and joint pain) for a few days. The fever then disappears and the symptoms usually subside without any consequence. In 10-20% of these cases, however, after an interval of 8-20 days with no symptoms, a second phase begins, characterised by signs that the central nervous system is affected (encephalitis, flaccid paralysis).
In children the disease tends to be milder. Mortality is on average 1-5%.
Impact on the population
Tick-borne encephalitis is an significant cause of viral infections of the central nervous system in the centre, east and north of Europe. In 1974-2003, there was a 400% increase in cases and in 1990-2007 an annual average of 8,755 cases were recorded in 19 European countries. The endemic areas are Austria, Germany, Sweden, Croatia, Finland, Norway, Hungary, Slovenia, Finland, Poland, part of the former USSR, Switzerland and the Czech Republic. The distribution area is also extending into suburban areas of Germany.
It also remains widespread in northern China and Mongolia.
According to the World Health Organization (WHO), about 10,000 to 12,000 cases of tick-borne encephalitis are reported each year, but this figure is probably much lower than the actual total. Most infections result from tick bites received during outdoor activities in wooded areas.
In Italy the cases are increasing, from 2 cases recorded in 1992 to 19 cases in 2002, and it is endemic in the provinces of Trento (41 cases in 1997-2006), Belluno and Gorizia.
Sources / Bibliography
- Modern Infectious Disease Epidemiology - (A. Krämer, M. Kretzschmar, K. Krickeberg;)
- Manuale per il Controllo delle Malattie Trasmissibili - (Rapporto ufficiale dell'APHA - D. L. Heymann)
- Encyclopedia of Virology - 3rd Ed. - (B.W.J. Mahy, M.H.V. Van Regenmortel et al.)
- Virology: Principles and Practice - (J. Carter, V. Saunders et al.)
- Foundations in Microbiology - 8th Ed. - (K. P. Talaro, B. Chess et al.)
- Vaccini e vaccinazioni - 3rd Ed. - (G. Bartolozzi et al.)
- Harrison's Principles of Internal Medicine - 16th Ed. - (Kasper, Braunwald, Fauci. Longo et al.).
- Infectious Diseases and Arthropods - 2nd Ed. – (J. Goddard)