[Formation of focus of West Nile fever on the territory of Saratov Region].

AIM: Detection of circulation of West Nile virus (WNV) on the territory of Saratov Region and prerequisites for formation of natural focus of West Nile fever (WNF), determination of the role of WNV in infectious pathology on the territory of the region. MATERIALS AND METHODS: of organs of small mammals, birds, blood-sucking arthropods for the presence of WNV markers (antigens and/or RNA) were studied. Clinical material from patients with symptoms not excluding WNF was studied. Donor blood sera samples were analyzed with the aim of detection of immune layer against WNV in population of Saratov Region. RESULTS: In 2010 WNV antigens were detected by EIA in 12 samples (7.1%) of mammal organ suspensions. In 2012 by using RT-PCR and EIA, markers of WNV were detected in 6 samples of bird brain suspensions (6.3%) and 1 sample of mammal organ suspension. Immune layer of population against WNV was 4% in 2011, 2.8% in 2012. In 2012 in 11 of 27 examined patients IgM against WNV in diagnostic titers and/or serconversion of IgG in paired sera were detected. In addition in 5 individuals virus RNA was detected in blood. Based on clinical, laboratory data and epidemiologic anamnesis 11 patients were diagnosed with WNF. CONCLUSION: The results obtained give evidence on the circulation of WNV on the territory of Saratov Region in 2010 - 2012. With the development of complications of WNF epidemiologic situation in 2012 an expansion of WNV areal onto the territory of the region took place and the process of formation of WNF natural foci is ongoing.

[Distribution of fleas in rodent colonies in the northwestern Precaspian region].

Distribution of fleas by their rodents hosts was investigated by field experiments using the method of individual labeling both the parasites and the hosts. The experimental site was situated in sand landscapes of the northwestern Precaspian region. Pattern of the contacts between rodents leading to the exchange of their ectoparasites was established. Average distance of the rodent migration from the site of its previous record was 54 m, while the distance of flea transfer for the same period was 142 m. The probability of host exchange by a flea under under its periodic attacks on host amounted to the value 0.500-0.889. The parameters of flea spreading in the northwestern Precaspian region and in the sand landscapes between Volga and Ural were shown to be similar. The ability of the flea Xenopsylla conformis to parasitizing on social vole without a significant decrease of its abundance was revealed.

[Phenomenon of Yersinia pestis biofilm formation in flea organism].

For the first time substantiated was the role of the phenomenon of Yersinia pestis biofilm--extracellular matrix envelope (EME)--formation as the basis that determines the nature of plague agent interaction with flea organism. Implication of vector's proventriculus in the process of biofilm formation was demonstrated. Ultrastucture of plague microbe conglomerates in flea proventriculus and midgut was analysed and uniform mechanism of their formation was elucidated. The role of Yersinia pestis biofilm in plague agent preservation in the gut of ectoparasites and soil of rodents burrows was discussed. PCR analysis confirmed the presence of plague microbe in plague infected corpses and fleas excrements stored at +8-10 degreesC for 7 years 9 months.

[Detection of arbovirus antigens in the mosquitoes and ticks inhabiting the Saratov Region].

The paper gives the results of a study dealing with the detection of the antigens of arboviruses of West Nile, Sindbis, Batai, Crimean-Congo hemorrhagic fever, a serocomplex of Californian encephalitis in the field material gathered in the Saratov Region in 2000-2006. The bloodsucking arthropods inhabiting the region were shown to be actively involved in the circulation of arboviruses in natural biotopes. The conclusion that it is expedient to organize an annual monitoring of arbovirus-induced infections in the areas where positive findings have been notified is justified.

[The ecology and prevalence of arboviruses on the territory of the Saratov Region].

The territorial spread of Tahyna, Batai, Sindbis, West Nile fever and Crimean-Congo hemorrhagic fever viruses throughout the Saratov region in 1998 - 2000 was analyzed. The characteristics of the epizootic activity of the natural foci of these arboviruses in different landscape zones (temperate forest-steppes, steppes and semi-deserts) were calculated. The species composition of small mammals, the natural reservoirs of the causative agents of arbovirus infections, was determined.

[Productivity of cultures of 4 species of fleas in laboratory breeding]. / Produktivnost' kul'tur chetyrekh vidov blokh pri laboratornom razvedenii.

When rearing fleas under laboratory conditions maximum productivity was observed in breeding cages with 100 fleas (80 females and 20 males). When the number of fleas was increased to 250 and 500 specimens the progeny decreased in number. At the ratio between males and females of 1 : 2 and 1 : 4 the productivity of fleas virtually did not change. Of all species studied fleas of X. cheopis are characterized by most high productivity. In all months of the year the average number of hatched fleas per one cage was 13-15 thou. of X. cheopis, 7-8 thou. of C. tesquorum, 1.5-2.5 thou. of X. skrjabini, and 3-4 thou. of Ct. wladimiri.

[Species composition and population dynamics of fleas on the small suslik in stable foci of plague on the Ergenin ridge]. / Vidovoi sostav i dinamika chislennosti blokh malogo suslika v mestakh stoikoi ochagovosti chumy na Ergeninskoi griade.

The paper presents results of investigations of fleas from Citellus pygmaeus obtained during epizootological surveys in 1972-1974 (the Ergenin ridge, Kalmyk ASSR). The most high number of the main species of fleas of C. pygmaeus was observed in the first year of epizootic on the background of great abundance of the host (over 30 specimens per 1 hectare). In the following years the decrease in the number of C. pygmaeus was accompanied by the fall in the fleas number. The distribution of different species of fleas in a microbiotope is uneven in various periods. In all periods in nests fleas of N. setosa were dominant while fleas of C. tesquorum were most abundant on the host. In burrows there was noted a change of dominant species: in the period of intensive epizootic of 1972 they were Ct. pollex and C. tesquorum, in 1973 during a slump of epizootic--C. tesquorum and N. setosa and in 1974 when epizootic was not discovered at all--N. setosa.