A Simple Spatial Model to Explain the Distribution of Human Tick-Borne Encephalitis Cases in Hungary

Abstract

Tick-borne encephalitis (TBE) is a common medical problem in Hungary and throughout much of Europe and Asia. This paper develops a geographic model that helps to predict the distribution of human tick-borne en- cephalitis cases in Hungary. The model is tested on a dataset of serologically confirmed TBE cases mapped by pa- tients’ residences. Case densities (incidence rates) are compared to predicted distributions of TBE derived from digital land-cover data. Maps are analyzed at the county level and on a smaller spatial scale. The analyses identi- fied three major factors that shape the geographic distribution of human TBE cases in Hungary. The most im- portant component is the distribution of forest habitat. TBE incidence correlates positively with the amount of forested habitat in each county. On a finer scale, the amount of forests within a 2500-meter radius of each town and village correlated significantly with TBE incidence rate. Based on these data, about 30% of the variation in TBE incidence is accounted for by the specific distribution of forest habitats in Hungary. Besides the distribution of forests, differences in human land-use practices among regions also affect the distribution of TBE cases. Ad- ditionally, because of the low transmission rate of the virus to humans, the perceived distribution of TBE cases is affected by random stochastic events. As a consequence of stochastic variation, meaningful patterns in the dis- tribution of TBE cases can be only recognized when data are analyzed over broader temporal and spatial scales. Key Words: Tick-borne encephalitis—Landscape ecology—GIS modeling—Hungary. Vector-Borne Zoonotic Dis. 6, 369–378. INTRODUCTION