An abortive form of tick-borne encephalitis (TBE)--a rare clinical manifestation of infection with TBE virus.

Tick-borne encephalitis (TBE) is one of the most important human infections of the central nervous system (CNS) and is endemic in several European countries, including a large part of Slovenia. In at least two-thirds of patients who develop CNS involvement, the disease has a characteristic biphasic course. Seroepidemiological studies on TBE virus infection in endemic areas of various European countries have demonstrated that asymptomatic infections are common. In some of these reports it was also suggested that there is an abortive form of TBE virus infection, which is manifested only by a febrile headache without meningeal involvement (i.e., the initial phase of illness without subsequent CNS involvement) and that it represents more than half of the cases of clinically manifested infection with TBE virus. The aim of this report was to evaluate patients who presented with the initial phase of TBE and monitor them for the appearance of the second, encephalitic phase of the disease. In 56/205 (27.3%) patients with febrile illness occurring after a tick bite, infection with TBE virus was demonstrated by the appearance of specific IgM and IgG antibodies against TBE virus during a follow-up period of 6 weeks. All 56 patients were diagnosed during the initial phase of TBE, however, only 1/56 (1.8%) had an isolated initial phase of TBE without subsequent CNS involvement, whereas 55/56 (98.2%) patients developed a clinically biphasic course of illness with CSF abnormalities (pleocytosis) during the second phase of the disease. Detailed epidemiological, clinical and laboratory characteristics of this patient with an abortive form of TBE virus infection are presented. The results of our study support the view that the abortive form of central European TBE is a rare clinical manifestation of TBE virus infection.