[Reservation forms of plague infectious agent in Tuva natural focus].

Data characterizing the reservation forms of plague infectious agent in Tuva natural focus are presented in the review. Yersinia pestis was shown to persist most of the year in Citellophilus tesquorum altaicus imago --the main carrier, getting into the animal organism only for a short time. An increased ability to aggregate in autumn and accumulate in clumps of C. tesquorum altaicus females that are more adapted to survive the cold season compared with males promote the persistence of the microorganism. The plague infectious agent in the altered form survives in the organism of females not only the winter period but also longer periods of time that is demonstrated by the facts of detection of it after 646 days of staying in the carrier. Moreover Yersinia pestis can persist for more than 400 days in the substrate of the nest of long-tailed ground squirrel infected by excrements and corpses of plague fleas. The substrate of the nest infected in summer-autumn period of the previous year may determine the primary infection of ground squirrels by plague infectious agent in the next epizootic season. On ground squirrels infected during contact with nest substrate, infection of intact fleas may be possible, and so the initiation of a new cycle of transmission of the infectious agent. Adaptation of the plague infectious agent to unfavorable existence conditions in the carrier is expressed in the changes of its morphology and ultrastructure that is evidenced by the facts of isolation of the infectious agent from corpses of fleas situated in the substrate, in the L-form, as well as results of phase-contrast and electron microscopy of the digestive tract of C. tesquorum altaicus.

[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.

[Role of fleas, the principal and secondary plague vectors, in the circulation of the causative agent in Siberian natural foci].

The paper reviews data on the role of fleas as the principal and secondary vectors of infection in the Siberian natural foci of plague. The role of Citellophilus tesquorum as the principal plague vectors in the Transbaikalian and Tuvinian natural foci is shown to be determined by their ecological characteristics (the degree of specificity to the main host, numbers, and natural infection) to a greater extent and by the rate of block formation to a lesser extent. The significance of principal and secondary vectors is estimated in the circulation of the causative agent in the monovectoral (Transbaikalian and Tuvinian) and multivectoral (Gorno-Altai) foci of plagues. It is suggested that the "microfocal" form (phenotype) of the agent's existence is characteristic of the Siberian natural foci where the rate of block formation does not generally show high indices. This phenomenon might be a basis for the long circulation of the plague microbe in the mountain (Tuva and Gorno-Altai) foci where protracted interepizootic periods have not been registered.

[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.

[Dispersal of the flea Ctenophyllus hirticrus and spreading of plague epizooties in Gorny Altai].

Gradual dispersion of an abundant flea species Ctenophyllus hirticrus specific to the Pallas's pika (the main plague carrier), is revealed in the Gorno-Altai natural plague focus on the territory, occupied by two populations of this lagomorph. Spreading of Yersinia pestis in these areas took place a short time later the rise of this ectoparasite's abundance. It is supposed that the colonization of these areas by C. hirticrus was one of the factors determined epizooties spreading within the focus and formation of new sites of stable Y. pestis preservation.

[Epizootological role of fleas in the Gorno-Altai natural plague focus (a review)]. / Epizootologicheskaia rol' blokh v Gorno-Altaiskom prirodnom ochage chumy (obzor).

Epizootological role of fleas in the Gorno-Altai natural plague focus (Sailugemsk focus) and numerous data on the flea viability are analyzed and generalized. Information concerning the flea natural infectivity with Yersinia pestis altaica is represented. Ecological peculiarities of some flea species parasitizing the main host, Mongolian pika Ochotona pallasi, and nature of their interrelations with Y. pestis are investigated. It is shown that the flea taxocenosis provides the permanent all year-round circulation of Y. pestis in the Gorno-Altai natural focus. Certain combinations of structural elements of the flea taxocenosis have a dominant significance in determination the circulation process at different phases of the annual epizootic cycle.

[Mechanisms of high sensitivity of Mongolian pika spp. (Pallas) to Yersinia pestis]. / Mekhanizmy vysokoi chuvstvitel'nosti mongol'skykh pishchukh k Yersinia pestis.

The regularities of the infectious process of plague in a sensible Pallas' pika species, are presented. The specific infectious process was shown to pass a number of phases. These phases are characterized by certain changes in the composition of the leukocytic pool of the peripheral blood, the immune system and the activity of the bactericidal systems of professional phagocytes. The infectious process in sensitive animals is accompanied by the formation of secondary relative immunodeficiency with a pronounced hypersuppressive component, which leads to disturbances in the cooperative interaction of immunocompetent cells; in its turn, it results in dysbalance in the cytokine system and, as a consequence, to irreversible disturbances in homeostasis, leading to the death of the infected animal.

[Brucellosis in Siberia and the Far East]. / Brutsellez v Sibiri i na Dal'nem Vostoke.

Epidemiological analysis has indicated that rat and reindeer brucellosis foci are of definite value in Siberia and the Far East in the liquidation of brucellosis ones. Foci of cattle and reindeer have been first established, evidence has been provided for the epidemiological significance of fifth-biological variant B. ovis and B. suis, as well as the ecological confinement of peculiar B. rangiferi cultures to the brucellosis foci in the Arctic. To plan antibrucellosis efforts, it is necessary to take into account the incidence of human infection, as well as the insidious circulation of the bacillus in the stock farms.

[The results of using an immunoenzyme method in an epizootiologic survey of natural Siberian foci of plague]. / Itogi primeneniia immunofermentnogo metoda pri épizootologicheskom obsledovanii sibirskikh prirodnykh ochagov chumy.

The approbation of the enzyme immunoassay in the study of diverse field material (corpses of animals, ectoparasites, soil, feces of birds of prey, etc.) for the presence of Yersinia pestis contamination has shown the advantages of this assay over the existing serological tests: the passive hemagglutination test and the antigen (or antibody) neutralization test. The use of the immunoperoxidase preparation obtained on the basis of staphylococcal protein A makes it possible to detect antibodies to Y. pestis in animals of various species known to be the main carriers, as well as less important ones, in the natural foci of plague in Siberia. The enzyme immunoassay is recommended for use in the study of not only active natural foci, but also territories, dangerous with respect to plague, as well as for controlling the state of such territories after the realization of relevant sanitation measures.

[Paradoxopsyllus scorodumovi (Aphaniptera) flea, an effective vector of plague in a Gorno-Altai natural focus]. / Blokha Paradoxopsyllus scorodumovi (Aphaniptera)--éffektivnyi perenoschik chumy v Gorno-Altaiskom prirodnom ochage.

A study was conducted on the fleas of P. scorodumovi and five local strains of the plague microbe, one of which is typical of the strains of the Altai subspecies and four are non-typical of this nidus. The fleas of this species are capable to transmit not only the plague agent of the strains typical of this nidus but also non-typical ones which differ in some biological properties and are avirulent for most carriers but Pallas's pika. Biological peculiarities of fleas of P. scorodumovi in addition to their high efficiency as vectors of the plague microbe enable us to associate the more active autumn epizooty with fleas of this species.