[Epizootological assessment of the possibilities of importing plague from Vietnam to Russia].

To assess whether the plague microbe with vectors or carriers can be imported from Vietnam to Russia, the authors consider the specific features of pathogen circulation in this country's biotopes varying in anthropogenic transformation. The idea that there were natural foci of plague in Vietnam dominated until the late 1990s. The small rat Rattus exulans that inhabits open stations and ensures a parasitic contact with the synanthropic representatives of the fauna was considered to be a major carrier. The recent years have provided conclusive proofs that plague foci are absent in Vietnam wild nature. Anthropurgic foci develop in the network of localities whose conditions are favorable to the existence of synanthropic rodents and the fleas Xenopsylla cheopis. Cases of the plague pathogen, FI antigen and its antibodies being detected in wild mammals are due to their parasitic contacts with synanthropic rats in the agrocultural area around the localities with running epizootias. These contacts are provided by X.cheopis only. Since 2003, there have been no reports on the incidence of human plague or its pathogen isolation from environmental objects in Vietnam. However, all conditions and prerequisites for the formation ofanthropurgic plague foci remain in this country. Further epizootological monitoring is required for appropriate services to rapidly and adequately respond if the epizootological or epidemiological situation of this infection changes.

[Natural foci of plague in India: epizootological characteristics].

In the first half of the 20th century, India was responsible for the incidence of plague in both Asia and the world. The early 21st century was marked by two new epidemic outbreaks of plague (in 2002 and 2004) in this country. The major characteristics of plagues in India, activation of which is a cause of new epidemic outbreaks and necessitates a continuous epizootological monitoring, are analyzed. Historical experience shows that lower focus on surveillance of natural foci of plaque, dissemination of unjustified views on sanitation of endemic areas, and much less their lack, can cause unpredictable epidemiological complications and considerable costs. More scrupulous attention should be given to the importation of goods from North and South India (where there were outbreaks of plague in 1994, 2002, and 2004) to Russia mainly in September to March.

[A possibility of using some pyrethroids to prevent plague in the Siberian natural foci of the souslik type].

Experiments have established that the pyrethroids deltamethrin and cypermethrin (decis and cimbush) may be used in the Siberian natural plague foci for not only emergency, but also early prevention of plague. This substantially expands and simplifies the possibility of organizing disinfection actions and reduces the cost of treatments. The findings are determined by the specific features of the biology and ecology of fleas inhabiting in the natural plague foci of the souslik type in a continental climate area. The specific features include the coincidence of preimago stages and the larger proportion of an adults to rodent nests; the low migration of imagoes from the inhabiting nests to the ground surface, only one insect generation that can develop within a comparatively short (4-5-month) warm period of a year.

[Organization of acaricidal treatments in two districts of the Irkutsk Region].

In the Irkutsk suburbs (a relatively southern area of the Irkutsk Region of the nosoarea of a natural tick-borne encephalitis focus), Ixodes persulcatus imagoes begin its activity in the first 10 days of April and usually finishes it in September. In 1996-2006, there was a trend for an increase in the number of the tick's bites in human beings, as well as three-year cycles of fluctuation of this index. In the Bratsk suburbs (a relatively northern area), the imago becomes active only in late April and the last sticking cases usually take place in late August. In 1996-2006, there was no increase in the number of tick attacks of the population, but the cycle period of this index being longer than in the Irkutsk suburbs. It has been earlier recommended that two all-round antitick treatments using cipermitrine-based compounds should be made in the area of epidemiologically significant objects in the Irkutsk suburbs in late April and in the third 10 days of May. It is sufficient to perform one treatment in the Bratsk suburbs in the third 10 days of May.

[Plague in China. Threat of transmission to regions of Siberia and Far East].

In China plague has been officially registered from 1754 (638 epidemics with total number of cases 2.5 millions and case-fatality rate 87.5%). Endemic areas started to form on the south of the country and then the disease gradually spread on seaside provinces, where to the end of the 19th century, due to reach of island territories and large international seaports, was characterized by pandemic spread. Epidemic manifestations of plague in China were observed during more than 200 years in 23 out of 36 administrative areas affecting continental and North-Eastern regions of the country, which are immediately adjacent to border of Russia. Pneumonic plague in Manchuria clearly demonstrated the role of transport communications in transmission of this deadly infection and possibility of its spread on border regions of Siberia and Far East. Lengthy country's border, intensive migration flows, large-scale international integration, developing of near-border trade, simplification of policy for transboundary traveling are the reasons for differentiated number of sanitary protective measures on administrative borders of Siberia and Far East.

[Conservation of Yersinia pestis in winter by Citellophilus tesquorum altaicus females and males].

Intersexual differences have been established in Citellophilus tesquorum altaicus Ioff (1936) from a Tuva natural focus in the accumulation of Yersinia pestis in fleas in autumn and its conservation during winter. The ectoparasites were infected and fed on the natural feeder - long-tailed Siberian souslik (Citellus undulates). Small wild animals and insects were infected with the strain Yersinia pestis 1-3226 typical of the focus. In winter fleas survived without the feeder under artificially created conditions of an uninhabited nest for long-tailed souslik. After each feeding, the ectoparasites were microscopically examined, by taking into account the individuals with aggregated agent - bacterial lumps, complete or partial blocks of the proventriculus. The experimental data showed with a high degree of significance that the females had survived the cold season better. Both before and after hibernation of the insects, the plaque agent in the aggregated state was also more frequently recorded in the females than in the males though the proportion of fleas with conglomerates significantly decreased in either sex during that time. If the best female survival and a higher proportion of females with Yersinia pestis are borne in mind, it should be recognized their greater role than that of males in conserving the plague agent during winter.

[Seasonal features of the time course of changes in the aggregated state of the causative agent of plague in the organism of Citellophilus tesquorum altaicus (Siphonaptera)]. / Sezonnye osobennosti dinamiki agregirovannogo sostoianiia vozbuditelia chumy v organizme Citellophilus tesquorum altaicus (Siphonaptera).

The data of experiments made in a Tuva natural plague focus with the main vector of the flea C. lesquorum altaicus during different seasons are analyzed. Ectoparasites were infected with the plague microbial strain typical for the focus and fed on natural nourishment, such as long-tailed sousliks. An analysis indicated that estimation of the parameter "the proportion of infected insects containing the causative agent at the aggregated state" is of greater informative value than is the recording of only sporadic gizzard "blocks". In experiments on fleas of a breeding of the current year, the conglomerates of the causative agent of plague were more frequently observed in males. All things being equal, the greatest efficiency of transmission of the microbe to the carriers of infection and the highest block formation in the fleas were observed in summer. The proportion of specimens with microbial conglomerates drastically increased in autumn during the preparation of the body of imagoes for hibernation. At this state, the microbe survived in the organism of a dormant carrier during winter. In spring, in the imagoes infected during the previous season, bacterial conglomerates were observed during the first feeds ten times more frequently than those in the insects of a breeding and infection of the current year.

[Differences between two populations of Citellophilus tesquorum altaicus from the Tuva natural focus of plague]. / Razlichiia mezhdu dvumia populiatsiiami Citellophilus tesquorum altaicus iz Tuvinskogo prirodnogo ochaga chumy.

Citellophilus tesquorum altaicus fleas from two natural (Karginsky and Barlyksky) populations have been studied. There are differences between the fleas of these populations in susceptibility to plague microbe. The adaptability and abundance of the causative organism in the body are higher in the fleas of the Barlyksky population. The sizes of the head are significantly higher in the females of the Karginsky population. There are no differences in this index between males. According to all 5 studies signs of chaetotaxia, the chaeta abundance is greater in both females and males of the Karginsky population. The fluctuating asymmetry is higher in the Barlyksky fleas that are more susceptible to the studied type of the causative agent of plague.

[Influence of a temperature factor on the vector capacity of the flea Citellophilus tesquorum altaicus]. / Vliaianie temperaturnogo faktora na vektornuiu sposobnost' blokhi Citellophilus tesquorum altaicus.

The impact of temperatures (2-3 to 23-25 degrees C) of flea keeping on their vector capacity was studied in the experiment. In hibernated fleas, the relationship of their vector capacity to the temperature of their keeping, estimated by the level of plague block in species and by the case rates of animals was insignificant, i.e. there is a trend for these indices to increase with elevated temperatures. In the fleas of current years breeding, the rate of block significantly increased with a rise of temperatures from 5-6 to 23-25 degrees C. There were also increases in the number of transmissions of a plague pathogen to susliks and in the number of animals with generalized infection with a rise in temperature up to 16-18 degrees C. The findings and constructed regression equations may predict the pattern of changes in the vector capacity of the flea C. tesquorum altaicus in the study range of temperatures in the enzootic area of a Tuva natural focus of plague.

[Short-term prediction of a change in the total stock of Daursk suslik fleas in the Transbaikal natural focus of plague]. / Kratkosrochnyi prognoz izmeneniia obshchego zapasa blokh daurskogo suslika v Zabaikal'skom prirodnom ochage chumy.

Based on 20-year studies of changes in the total store of the imago of Daursk souslik fleas in the Transbaikal natural focus of plague and on observations of variations in some environmental factors, equations of the short-term prediction of the size of fleas have been constructed for each month (from May to September inclusive). The equations include from one to three predictors that significantly influence the dynamics in the abundance of exoparasites. A nonlinear regression analysis was used for statistical data processing. The results and reliability of short-term stepwise prediction of the size of souslik fleas in the Transbaikal natural focus of plague from 1978 to 1987 are retrospectively considered.

[Ecological factors that influence the dynamics of the total store of Daursk suslik fleas in the Transbaikal natural focus of plague]. / Ekologicheskie faktory, vliiaiushchie na dinamiku obshchego zapasa blokh daurskogo suslika v Zabaikal'skom prirodnom ochage chumy.

Based on 20-year (1967-1987) studies of the dynamic of the total store of the imago of Daursk souslik fleas in the Transbaikal natural focus of plague and of changes in the abiotic and biotic parameters of the environment, the authors have identified factors that statistically significantly influence the study processes. The analysis was made by the nonlinear multiple regression test. One to three predictors of flea abundance have been detected for each month from May to April inclusive.

[Seasonal changes in the resistance of a Drosophila population to low temperatures and their association with fertility]. / Sezonnoe izmenenie ustoichivosti populiatsii drozofily k nizkoi temperature i ee sviaz' s plodovitost'iu.

Significant genetic variation in resistance to cold was detected in samples collected from a natural Drosophila population in spring, summer, and autumn. In the summer sample, phenotypic variation was determined by genetic factors; in the summer and autumn samples, exclusively by environmental factors. Flies collected in spring had the highest longevity at low temperatures. In summer, their longevity at low temperatures was drastically reduced but it was shown to increase in autumn. Cold-resistant flies had high fertility in spring and low fertility in autumn. The seasonal differences in resistance to cold were genetically determined and are probably caused by natural selection.

[Asymmetry of the chaetae in fleas (Citellophilus tesquorum) as a possible marker of their capacity for blocking]. / Asimmetriia shchetinok u blokh (Citellphilus tesquorum) kak vozmozhnyi marker sposobnosti k blokoobrazovaniiu.

The fluctuating asymmetry was studied according to two bilateral numeric features of chaetaxy in groups of female Citellophilus tesquorum fleas. One group included insects with the recorded gizzard block during infection with the virulent plague agent strain. The fleas with the block were characterized by considerably higher levels of fluctuating asymmetry as compared with those without fleas.

[Phenotypic and genotypic structure of a natural Drosophila population with respect to the reaction of individuals to an increase in population density and its seasonal change]. / Fenotipicheskaia i genotipicheskaia struktura prirodnoi populiatsii drozofily po reaktsii osobei na uvelichenie plotnosti i ee sezonnoe izmenenie.

In spring and summer, the natural population of Drosophila studied exhibited a high level of phenotypic and genotypic heterogeneity with regard to change of individual fertility with an increase of density of adult flies. From spring to autumn, the level of genotypic variation decreased. In autumn, all phenotypic variation resulted from environmental factors. In spring, individuals sensitive to overcrowding, adapted to low density, and highly fertile in low-density conditions prevailed in the population. In summer and autumn, the population was mostly composed of individuals with opposite characteristics. On the basis of the obtained results, a conclusion on operation of cyclic density-dependent selection in the population examined was made. Selection's functional role in control of seasonal population size dynamics is discussed.

[An experimental study of the ability of the hybrid crosses of Citellophillus tesquorum fleas of 2 subspecies to transmit the causative agent of plague]. / Eksperimental'noe izuchenie sposobnosti gibridov ot skreshchivaniia blokhi Citellophillus tesquorum dvukh podvidov peredavat' vozbuditelia chumy.

The ability to transmit of plague bacillus was studied in the first-, third- and fourth-generation hybrids bred from C.t.altaicus and C.t.sungaris. The fleas were inoculated with two virulent strains from the Tuva and Transbaikal natural foci of plague. The bacillus was demonstrated to infect the hybrids, form gizzard block, and be transmitted to white mice, causing the animals' death.