TBE virus is the causative agent of early summer meningoencephalitis (TBE). The tick is considered the main vector of the flu-like disease. The course is very variable. In the worst case, severe complications occur, including long-term damage to the nervous system.
What is the TBE virus?
TBE (early summer meningoencephalitis) is one of the notifiable infectious diseases in Germany. The causative virus comes from the Flaviviridae family. Its structure consists of a single, enveloped RNA strand. There are three subtypes of TBE: Far Eastern subtype, Western subtype and the Siberian subtype. The virus uses insects as a natural intermediate host for transmission to the final host. Through contaminated saliva, mainly ticks transmit TBE virus to humans during their blood meal. There is a close relationship between the TBE virus and the causative agents of dengue and yellow fever. In Germany alone, people fall ill every year in the three-digit range. Moreover, not all cases are registered due to the extremely variable nature of the health effects. At the beginning, symptoms are additionally very unspecific. Often, however, no disease develops despite the pathogen entering the bloodstream. The incubation period is about one to three weeks until the first signs of disease germinate. Due to the time difference and the unspecific symptoms, there is a risk of confusion with a common summer flu. Therefore, the contact of the virus with the immune system often goes completely unnoticed. The tick called common wood tick (Ixodes ricinus) is considered the main vector. Among the intermediate hosts, there are numerous species that also carry the pathogen. Members of the leather tick genus (Argas and Ornithodorus) are also occasionally infected.
Occurrence, distribution, and characteristics
The first observed case of TBE dates back to 1931. Forest workers in Neunkirchen, Saarland, became ill with paralytic symptoms after tick bites. The TBE virus was first isolated and catalogued in 1949. The main components of the protective viral envelope are the proteins envelope protein E, core protein C and the membrane protein. The Far Eastern subtype is still considered the most dangerous representative of the TBE virus. The lethality of this variant is 20 percent. Its distribution area extends from Russia to China, Korea and Japan. In Europe, the less dangerous Western subtype dominates with a reduced number of fatalities among infected persons of only 2 percent. Being bitten by a tick in high-risk areas does not equate to infection. Estimates put the infection rate at 1 : 150, with only 30 percent of those infected experiencing a successful infection by the pathogen. Among them are for the most part men. Only one in three victims is female. This trend can also be observed in the number of deaths. Overall, the male sex is clearly in the lead with a 75 percent share. In older people over the age of 50, there is an accumulation of longer and more severe courses of the disease. In Germany, there is an increased risk of infection in the southern states. According to the Robert Koch Institute, Bavaria, Baden-Württemberg and southern parts of Hesse and Rhineland-Palatinate are considered risk areas. Here, the probability of TBE infection is measurably above average. In general, the distribution of the pathogen in tick populations covers large parts of Europe with a concentration in the central and eastern areas. The parasites preferentially lurk in grasses and bushes during spring and early summer. Wooded areas and private gardens offer numerous hiding places for them. Theoretically, there is a risk of infection everywhere in the open air. Leisure activities of people with short clothing therefore offer an optimal attack surface for the ticks. It is therefore advisable to check for ticks after spending time in nature and, if necessary, remove them with tick forceps or other aids. As a secondary source of infection, infected milk products from sick animals pose a danger. Consumption of raw milk products leads to disease through oral ingestion if sufficient TBE pathogens are present. Due to pasteurization, the probability of transmission on German territory is extremely low.A striking feature is an endemic clustering of cases within risk areas near rivers. The cause of this association remains unclear.
Diseases and complaints
Despite the statistically low chance of infection with serious consequences, early summer meningoencephalitis is a serious disease. Infected individuals cover a wide spectrum of symptoms in severity and duration. In the first stage, the supporting features are fatigue, nausea, and headache and aching limbs accompanied by fever. Initially, the characteristics resemble those of a common summer flu. Usually it remains at this intensity of expression and the disease subsequently subsides. A few weeks later, a second outbreak may occur. During entry into the second stage, there is an attack on the central nervous system. Increased fever as well as intense headaches are typical. In addition, there is a stiff neck. Often these symptoms are directly related to meningitis (meningitis). In particularly severe cases, the focus of inflammation spreads to the spinal cord and brain. Nerve roots are also affected. The first signs of sensory and motor deficits are the consequence. Speech disorders and swallowing difficulties may occur. Paralysis of individual parts of the body and psychological effects occur in the brain and spinal cord, depending on the localization of the infestation. The lethality within severe cases is about 30 percent. Thus, individuals in this phase of the disease have the poorest chance of recovery. Complete recovery from all major symptoms and long-term sequelae occurs in about one in five long-term patients. Almost half of all affected persons have to live with chronic sequelae of TBE. Neurological damage is in the foreground. Depending on the severity, these manifest themselves in breathing difficulties, numbness and disturbances of the sense of balance. Paralysis and speech impairments may persist. Sporadically, however, spontaneous recovery from all symptoms may occur.
