To the knowledge of the common hamster (Cricetus cricetus Linné, 1758; Rodentia) as host of leptospirosis in Czechoslovakia.

A total of 1288 hamsters (Cricetus cricetus), coming from two regions of Czechoslovakia, were serologically investigated on the presence of leptospirosis. In 1114 hamsters from eastern Slovakia, where an outbreak occurred and local populations lived quite atypically, there was 31.8% positivity, in 174 animals from central Moravia, where the populations were at higher levels but lived normally, the positivity amounted to 17.2%. The serological positivity increases proportionately to the weight, i.e. to the age of the animals. The serovar grippotyphosa was dominant in them (29.6% of examined hamsters), while 6.0% were positive for L. pomona, 1.0% for serovars from the serogroup Sejroe, 0.2% for L. sorex-jalna and L. bataviae respectively, and 0.1% for L. bratislava. The hamsters from central Moravia were positive only for the serovar grippotyphosa. Antibodies in lower titres against L. pomona, having the character of coagglutinations, were simultaneously detected in some hamsters positive for L. grippotyphosa. In Czechoslovakia the common hamster is one of the potential hosts of L. grippotyphosa, its importance increasing during severe outbreaks, when the incidence of infection with L. grippotyphosa in hamster populations increases and the animals inhabit most varied types of biotopes and transfer to synanthropic way of life.

The structure of tick-borne encephalitis (TBE) foci in Central Europe.

The investigations on the structure of TBE foci were carried out in the localities Jívová (northern Moravia), Topolcianky and Zírany (Tribec Mountains), and environs of Debreczén (Pannonian lowland, Hungary). The biphasic activity curve of Ixodes ricinus, characteristic for the central European conditions was confirmed in all three types.In some localities two or three tick species as vectors come into consideration and the unequal seasonal occurrence of individual species results in a permanent presence of virus-harbouring ticks in nature throughout the year.The average population density of ticks per hectare in a focus near topolcianky in mid-April, 1969, reached 46,000 nymphae and 50,000 adults. About 1% of the tick population were found to be viruliferous.Great differences were found in the composition of plant communities, mammalian synusies and in the population density of small mammals and ticks within the regions studied.Each elementary focus consists of many "microfoci" where the territories of individual host species overlap in space and time. Nests in tree holes and underground probably also belong to these microfoci. The maintenance hosts and indicators in each type of focus are mentioned. Free-living Carnivora can be considered as incidental hosts in each type of focus.

The autecology of small rodents and insectivores of the Tribec mountain range.

Small rodents and insectivores have become the main reservoirs of tick-borne encephalitis virus. In order, therefore, to demonstrate the dynamic and structural changes occurring in a natural focus of tick-borne encephalitis, information has been collected on the distribution, habitat, life-cycle, population density and extent of tick infestation of the rodents and insectivores that inhabit the Tribec region and adjacent parts of the Hronský Inovec Mountains. The following mammals are discussed: Sciurus vulgaris, Citellus citellus, Glis glis, Muscardinus avellanarius, Mus musculus, Micromys minutus, Apodemus flavicollis, A. sylvaticus, Microtus arvalis, Pitymys subterraneus, Clethrionomys glareolus, Arvicola terrestris, Sorex araneus, S. minutus, Neomys fodiens, N. anomalus, Crocidura suaveolens, C. leucodon, Erinaceus roumanicus and Talpa europaea. Many of these are important reservoirs of virus.

The relationship between the tick-borne encephalitis virus and the ticks and mammals of the Tribec mountain range.

The basic problem in the study of tick-borne virus diseases is to establish where the virus is maintained in nature. In general, this focus will be found where there are large and relatively stable populations of ticks, small rodents and insectivores. In the Tribec region the principal vector of tick-borne encephalitis (TBE) is Ixodes ricinus, although other species can circulate the virus under suitable conditions. The virus can persist during winter either in starving nymphs or adults or in non-starving larvae or nymphs. It can also persist in hibernating mammals, but this is a less important mechanism. Among the mammals, the insectivores (hedgehogs, shrews and moles) and certain rodents are hosts of ticks and reservoirs of TBE virus of great importance. During spring, game and farm animals play an important role and birds are important hosts when the number of small mammals is low. Thus the survival of TBE virus depends on a complex interaction of varying populations of tick vectors and vertebrate hosts that occur in different habitats influenced by different environmental conditions.