Longitudinal study of natural foci of Central European encephalitis virus in West Slovakia.

A total of 2922 small terrestrial mammals of 12 species were collected in six localities of West Slovakia between 1981 and 1986. When examined for the prevalence of neutralizing antibodies (NA) to Central European encephalitis (CEE) virus we found that 14.6% had antibody. Nearly all (97%) of the 426 animals with antibody were Clethrionomys glareolus, the most abundant species (52.6% of mammals collected, 15.1% of those with antibody). Apodemus flavicollis (22.5% of mammals collected, 18.1% of those with antibody), Apodemus sylvaticus (14% of mammals collected, 8.5% of those with antibody), and Microtus arvalis (5.5% of mammals collected, 3.3% of those with antibody). In all locations studies the most abundant tick found on small mammals was Ixodes ricinus (larvae and nymphs). Less abundant, but present in all studied sites, were larvae and nymphs of Dermacentor reticulatus and Haemaphysalis concinna. Six strains of CEE virus were isolated from tissues of animals: four from Clethryonomys glareolus and one each from Apodemus flavicollis and Sorex araneus. Three of six isolates were from animals collected in February; none of the six had detectable neutralizing antibody to CEE virus. We discuss these observations with regard to possible mechanisms of persistence of CEE virus.