Tick-Borne Encephalitis-Review of the Current Status

Abstract

The tick-borne encephalitis virus (TBEV) is the arboviral etiological agent of tick-borne encephalitis (TBE), considered to be one of the most important tick-borne viral diseases in Europe and Asia. In recent years, an increase in the incidence of TBE as well as an increasing geographical range of the disease have been noted. Despite the COVID-19 pandemic and the imposition of restrictions that it necessitated, the incidence of TBE is rising in more than half of the European countries analyzed in recent studies. The virus is transmitted between ticks, animals, and humans. It seems that ticks and small mammals play a role in maintaining TBEV in nature. The disease can also affect dogs, horses, cattle, and small ruminants. Humans are incidental hosts, infected through the bite of an infected tick or by the alimentary route, through the consumption of unpasteurized milk or milk products from TBEV-infected animals. TBEV infections in humans may be asymptomatic, but the symptoms can range from mild flu-like to severe neurological. In Europe, cases of TBE are reported every year. While there is currently no effective treatment for TBE, immunization and protection against tick bites are critical in preventing this disease.

Keywords: Flaviviridae; Ixodes; TBEV; arbovirus; tick-borne encephalitis; vector-borne.

Figure 2

The pie chart shows the abundance of identified TBEV strains within subtypes. Far Eastern group: 88 TBEV strains; European: 47 strains; Siberian: 33 strains; 886-84 Baikalian 2: 11 strains; Himalayan: 2 strains; 178-179 Baikalian 1: 1 strain and Obskaya 2971: 1 strain [10,16,19,24].

Figure 1

Schematic structure of the TBEV virion, the viral genome (RNA) and the C protein form a nucleocapsid surrounded by a lipid envelope in which glycoproteins E and M are embedded.

Figure 3

Transmission of TBEV in the life cycle of ixodid ticks, shaded fields indicate the host group characteristic for particular developmental stages of ticks.