IS THERE AN OUTBREAK OF TICK-BORNE ENCEPHALITIS IN PERNIK DISTRICT, BULGARIA? FOUR CASES REGISTERED FOR A PERIOD OF FOUR YEARS – CLINICAL MANIFESTATIONS AND EPIDEMIOLOGICAL RELATIONS

Abstract

In Europe, the number of tick-borne encephalitis (TBE) cases has been increasing in the last decade, and the number of endemic areas has also been increasing. Bulgaria, located in southeastern Europe, is not in the TBE endemic area. However, sporadic TBE cases have been occasionally detected. The disease has a natural-focal nature, pronounced seasonality, with a vector- Ixodes ticks that transmit the infection from animals to humans. TBE is severe infection with specific lesions of the central nervous system (CNS), with residual phenomena and high lethality. The first cases of TBE in Pernik district were registered in 2015. The aim of the study is to consider clinical cases of TBE in Pernik district during period 2017-2020, to look for an epidemiological link between them and to monitor severity of the infection. We briefly present the most characteristic clinical and laboratory features of four laboratory confirmed cases of tick-borne encephalitis in the last 4 years. The mean age of all of the patients was 56. All four cases were observed in May, June, and July. They proceeded relatively smoothly with a favorable outcome, without paresis or paralysis of the limbs, without seizures or loss of consciousness. In the first case of computed tomography, no pathological changes in the brain were observed, while in the other three cases multiinfarction encephalopathy, evidence of initial cerebral edema and two porencephalic foci were found. Two of the patients had meningoradicular irritation with positive symptoms of Kerning, Brudzinski and Babinski, while in the other two patients these symptoms were absent. In all four cases there was a classic change in the hemogram: moderate leukocytosis with granulocytosis, and in the study of cerebrospinal fluid - a slight increase in total protein, moderate pleiocytosis and normal values of sugar and chloride. Only one of the patients was reported to be bitten by a tick, and the other three were most likely infected through food (raw goat's milk). Confirmed cases of TBE in Pernik district, although isolated, show that the virus is circulating in this region. This is facilitated by a number of factors: climate change, activity of the epizootic process in the tick population, different species of vertebrates in natural foci; presence of a large number of goats infected with viruses. Although cases of TBE have been reported only sporadically due to a lack of sufficient testing, TBE virus is circulating in Pernik district. Comprehensive measures are needed: through good awareness of clinicians, search for infection in patients with viral meningitis, increased screening of raw milk by the Bulgarian Food Safety Agency, future studies on ticks and farm animals for presence of TBE in this region. This study is a prerequisite for future research in this direction.