The meadow tick Dermacentor reticulatus in natural foci of tick-borne encephalitis in Udmurtia

In southern Udmurtia, where occur both Dermacentor reticulatus and Ixodes persulcatus, in the years of high abundance of small mammals feeding periods of larvae and nymphs of these ticks coincide completely. The duration of simultaneous parasitism of preimago of the above ixodid species on animals is of epidemiological significance as far as within this period the infection of young stages of D. reticulatus with the virus of tick-borne encephalitis occurs. This is confirmed by the isolation of I strain of the virus from D. reticulatus collected at the state of engorged nymphs on hosts common with I. persulcatus and moulted in the laboratory.     

Biological properties of strains of tick-borne encephalitis virus isolated in the natural foci of the eastern part of the Russian plain

Strains of tick-borne encephalitis virus isolated in the natural foci of infection in the eastern part of the Russian Plain (the Kirov region) were examined for their biological properties. The strains examined were 69 strains isolated from ticks Ixodes persulcatus, 62 strains obtained from patients with the clinically manifest form of tick-borne encephalitis and 56 strains isolated from the blood of patients with the inapparent form of infection. Comparative studies on laboratory animals (albino mice, golden hamsters, suckling guinea pigs and other mammals) as well as comparative serologic studies provided evidence which suggested that all virus isolates from the Kirov region were antigenically identical with the strain "Sofin" isolated in the Far East and represent thus a single causative agent of the tick-borne encephalitis virus infection. This strain of virus is supposed to exist in two variants, in dependence on ecological conditions: one of these variants is the eastern variant (strain Sofin and strains from the Kirov region) and the other one is the western variant of tick-borne encephalitis virus.     

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

Summary The investigations on the structure of TBE foci were carried out in the localities Jívová (northern Moravia), Topolianky and írany (Tribe 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 topolianky 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.     

Modern problems in the study of tick-born encephalitis natural foci

A new conception of natural focus as anthropo-parasitic system is given by an example of tick-born encephalitis. Problems of natural foci classification and zoning of focal territories, as well as patterns of ecological relations in these systems, are considered. Causes and factors affected expansion of the infection are analyses.     

Characteristics of the relation of tick-borne encephalitis morbidity to natural factors

Data and tendencies characteristic of relationship between the severity of the course of tick-borne encephalitis and a number of biotic and climatic factors have been revealed by the method of information analysis. On the basis of relationships established in this study the authors make a suggestion concerning two most important stages in the formation and manifestation of the clinical features of tick-borne encephalitis in different areas of endemic territories, linked, on one hand, with the population selection of the infective agent and, on the other hand, with temperature conditions and the duration of the cold season.     

Functional organization of natural tick-borne encephalitis foci and prognosis of their epidemic manifestation: analysis of one-dimensional temporal series of infection

Temporal extrapolation prognosis of tick-borne encephalitis diseases in the Primorye territory and its certain regions is made by means of autoregression models. The results obtained shows good prospects of used methods and models.     

The role of birds in the maintenance of tick-borne infections in the Tomsk anthropurgic foci

The role of birds in the focus of tick-borne infections was studied from 2006 to 2011. The frequency index of ticks carried by ground dwelling birds is about 49.7%. The index of their abundance is 3.8. The larvae of ticks have been found on birds in 43.8% of cases. Nymphs and adult ticks have been found in 39.9 and 16.3%, respectively. It was revealed that Ixodex pavlovskyi was transferred and dominated in the urban microfoci because of its ornithophily. The markers of infectious agents have been recorded in 42 of 60 bird species under study.     

Methodological aspects in the study of the natural foci of zoonoses

Conceptions of different authors on the natural focus of zoonosis infections are analysed and an improved definition of this phenomenon is proposed. The natural focus of disease is the antropoecosystem of certain hierarchic level (biosocial system), where the existence and appearance of the infection agent is supported and the disease is realized in people at certain infection rate.     

Cyclic morbidity of certain natural foci infections in the Russian Federation

A special search program for finding out hidden periodicity was used; such program made it possible to put in order the apparently chaotic sequence of numerical data that are summed up to form the resulting curve, the latter reflecting the actual dynamics of the epidemic process. The cyclic character of morbidity in tick-borne encephalitis, hemorrhagic fever with the renal syndrome (HFRS), tularemia and leptospirosis among the population of Russia for the last 45-54 years was revealed. In tick-borne encephalitis cycles lasting 17-18 years with secondary wave having the period of 3-4 years were found out. In HFRS the main cycle lasts for 16 years and has secondary rises every 3-4 years. In tularemia the main cycles last for 17 years; secondary rises and drops in morbidity were also found to occur every 3-4 years. In leptospirosis regular rises and drops in morbidity were found to occur every 4-5 years.