Editorial: Tick-borne encephalitis - the most relevant to public health flavivirus infection in the EpiNorth region
Published: 16.08.11 Updated: 16.08.2011 13:21:31
Associated Editor, EpiNorth Journal
Centre for Communicable Diseases and AIDS, Lithuania
Citation: Žygutienė M. Tick-borne encephalitis - the most relevant to public health flavivirus infection in the EpiNorth region. EpiNorth 2011;12: 31-2.
Ticks are considered to be second main vector after mosquitoes in spreading human infectious diseases in the world. Ixodes ricinus is the most important tick species for the transmission of tick-borne diseases to humans in Europe. It may transmit a number of disease agents including two of the most widespread: tick-borne encephalitis virus (TBEV) and Lyme borreliosis spirochetes. Ixodes ricinus ticks are primarily mostly restricted to forested areas and prefer heterogeneous broad-leaved or mixed forests with dense undergrowth and leaf litter providing sufficient humidity. In natural foci, the pathogens circulate among ticks and their vertebrate hosts. Ticks are more common in the spring and autumn months (1,3).
Tick-borne encephalitis (TBE) poses one of the most important health threats in the northern hemisphere. TBEV circulates through a complex cycle involving small mammals, ticks, and large mammals. This virus is mainly transmitted to humans by the bite of an infected tick. Often the tick bite goes unnoticed. Infection can also be transmitted through consumption of unpasteurized milk and milk products. TBEV is a flavivirus in the family Flaviviridae and has 3 subtypes, each of which has its own ecology, clinical presentation, and geographic distribution: The European virus (previously Central European encephalitis virus, TBEV-Eu), the Far Eastern virus (previously Russian spring-summer encephalitis virus, TBEV-Fe), and the Siberian virus (previously West Siberian virus, TBEV-Sib). TBEV-Eu is closely associated with I. ricinus ticks, and TBEV-Fe and TBEV-Sib with I. persulcatus ticks. I. ricinus are spread in large parts of Europe extending as far as Turkey, northern Iran, and the Caucasus in the southeast. I. persulcatus occurs in Eastern Europe, Siberia and as far to the east as Japan and China. There is an overlapping zone of I. ricinus with I. persulcatus from the Northern Baltics to the Urals. Each tick species has preferred environmental conditions and biotopes that determine the geographic distribution of the ticks and, consequently, the risk areas for tick-borne diseases (2,3).
Between 1990 and 2009 a total of 169,937 cases of TBE were reported in Europe, i.e. an annual average of 8,497 cases. Of these, 2,815 cases (33%) occurred in Europe excluding Russia. During 1976 to 1989, the annual averages were 2,755 and 1,452 cases in Europe and Europe excluding Russia, respectively. The reported cases over the last three decades correspond to an increase of 318% in Europe including Russia and 193% in Europe without Russia (4).
In this issue the EpiNorth journal provides a series of articles on TBE from the Russian Federation (Novgorod oblast and Republic of Komi) and Finland.