Morphology of a natural focus of Pomona leptospirosis in a steppe area

The natural focus of Leptospira pomona infection has been found to include areas of the forest-meadow flood plain where the circulation of leptospires is constantly maintained among small mammals (the nucleus of the focus). A high level of Leptospira carriership (17.7%) among the animals has been registered in the central part of the flood plain and near the terraces, these areas having the most favorable conditions for the development of epizootic leptospirosis.     

The self-maintenance of natural foci of leptospirosis

The specificity of infection of individual species of small mammals with definite serogroups of leptospires has been shown. The intensity of the epizootic process has been found to depend on the number of animals in the population. The mechanisms of the self-regulation of the epizootic process in natural foci are explained.     

Rabies prognosis in western Siberia and the regulatory factors of the epizootic process

In this article the regulatory factors of the epizootic process are considered and the spatial-temporal prognostication of rabies infection in the region is proposed on the basis of data on rabies morbidity among animals, the purchase of skins of carnivorous animals for 20-25 years, virological experiments on wild animals, calculation of the number of carnivores and small mammals, as meteorological observations. The study has shown that a variety of animal species serving as hosts for the virus and its population differences contribute to the stable existence of the infection. Rabies morbidity has been found to be positively linked with its preceding level, the number of wild animals, the height and hardness of the snow cover and negatively with the number of small mammals.     

A natural focus of icterohemorrhagic leptospirosis in the floodplain of the lower Don and means for its eradication

An active natural focus of icterohemorrhagic leptospirosis has been detected in the area of fish-breeding ponds in Rostov Province, where the intensive epizootic among the population of Norway rats is observed the whole year round (574 animals have been examined, 56 cultures have been isolated). The epizootic process reaches its highest intensity in autumn (the proportion of infected animals exceeds 50%). This natural focus in the area of fish-breeding ponds is epidemiologically dangerous. The limitation of its infectious potential is possible by means of poisoned baits.     

Results of prolonged study of flood plain-swamp endemic foci of tularemia, and its prophylaxis in the Leningrad Region

The results of a prolonged (more than 18 years), comprehensive study have revealed that stable natural foci of tularemia in backwater swamps are widely spread in the Leningrad region. These foci are located in the narrow swampy flood-plains of small watercourses with adjacent meadow areas among forests. Water from such small watercourses can often serve as the indicator of the epizootic process: during the above-mentioned period 346 Francicella tularensis strain have been isolated from water and 86 strains from small mammals. The water factor plays an important role in the circulation of the infective agent in natural foci.     

Natural foci of diseases: the development of the concept at the close of the century

E. N. Pavlovski?'s concept of natural focality of diseases and the development of general knowledge about natural foci and their structural (components), functional (mechanisms of pathogen maintenance), and ecosystem-related organization (assortment and interrelations of ecosystems) are reviewed from principal (in authors' opinion) aspects. The 60-year history of this theory includes three stages at which its scope and contents differed. At the first stage, it concerned transmissible zoonoses. It had been assumed that structurally, natural foci necessarily include the pathogen-vector-host triad, and the functioning of the focus is provided for by only pathogen circulation in terrestrial ecosystems. At the second stage, it became clear that vector is not a necessary structural component of any focus (an example of nontransmissible diseases), although the functioning of foci remained to be unequivocally attributed to the continuous pathogen circulation among animals of terrestrial ecosystems. The third stage is characterized by an understanding that, in general, the presence of a warm-blooded host in the focus is also unnecessary for pathogen survival, and natural foci can be represented by soil and aquatic ecosystems. The only necessary and specific component of any natural focus is the pathogen population. In this context, modern views on natural focality of diseases are reviewed, and the essence of the terms "natural focus" and "epizootic process" is defined. It is proposed to distinguish the phases of pathogen reservation and epizootic spread (circulation) in ecosystems of any type. The current state of this concept provides evidence that, in general biological terms, studies on natural focality of diseases belong to one of the fields of symbiotology.     

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.     

Epizootological role of fleas in the Gorno-Altai natural plague focus (a review)

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.     

Long-term dynamics of the epizootic process in natural foci of ixodid tick borreliosis in mountain taiga forests of the Middle Ural

During eleven spring-summer seasons (1992-2002), the dynamics of the epizootic process in natural foci of ixodid tick-borne borrelioses (ITBB) were studied in taiga forests of the Middle Ural (Perm Province, Russia). In these foci, Borrelia garinii and B. afzelii circulate, and their main vector is the Ixodes persulcatus tick. Main parameters of the epizootic process were calculated for each season. In four seasons (1993, 1996, 1999 and 2002), the parameters characterizing the abundance of unfed nymphs and adult ticks, as well as the prevalence of Borrelia in them, density of infected ticks, and approximate total number of Borrelia in them proved to increase essentially and simultaneously. These seasons were preceded by the years of population peaks in forest small mammals (1992, 1995, 1998 and 2001), especially in the Clethrionomys glareolus vole, the dominant species in the local fauna of these mammals and the main reservoir host of Borrelia. Apparently, the possibility of horizontal transmission of the ITBB agents sharply increased in such years, and this resulted in the intensification of their dissemination.     

Experience with a bacteriologic and serologic study of a tularemia epizootic in rodents in a natural focus of the meadow and field type

The autumn-winter (1977-1978) tularemia epizootic in small murine rodents was revealed and studied at the natural focus of the meadow and field type in the south of the Moscow Region. The efficacy of the serologic method (the antibody neutralization test) of studying the organs of the caught rodents and the bodies of dead rodents was found to be greater than that of the traditional bacteriologic methods (26.6% and 9.6%, respectively). The serologic study of 908 specimens of avian excrements collected during the period from autumn to spring (1977-1978) revealed that tularemia antigen could be constantly detected, starting from October. The serologic method was effective when used both for the early and retrospective detection of the infective agent and allowed to characterize the epizootic process in greater detail.     

Epizootic situation and prospectives of rabies control among wild animals in the South of Western Siberia

The analysis of the epizootic situation in rabies in the south of Western Siberia during the period of 1990-1999 was carried out on the basis of the analysis of statistical data, field observations and virological investigations. Foxes were found to be the principle virus host and in the steppe areas they probably shared this role with corsac foxes. No data on other orders of mammals taking part in the virus circulation were obtained. The foxes population structure of the territory of the above-mentioned region were studied. The epizootic process was shown to have a cyclic character which corresponds to the models, proposed by foreign researchers for Western Europe. The effectiveness of different methods used for the control of rabies among wild animals was considered. As shown by this study, due to the population ecology of foxes and corsac foxes on the above-mentioned territory the best effect should be expected from measures aimed at frequency limitation of these animals, and not from vaccinal prophylaxis. As an alternative, the possibility of non-interference in the circulation of the virus within the limits of the natural focus in combination with timely measures for the protection of domestic and agricultural animals, as well as humans, from infection was considered.     

Enemies mediate distance- and density-dependent mortality of tree seeds and seedlings: a meta-analysis of fungicide,insecticide and exclosure studies

Conspecific negative distance- and density-dependence is often assumed to be one of the most important mechanisms controlling forest community assembly and species diversity globally. Plant pathogens, and insect and mammalian herbivores, are the most common natural enemy types that have been implicated in this phenomenon, but their general effects at different plant life stages are still unclear. Here, we conduct a meta-analysis of studies that involved robust manipulative experiments, using fungicides, insecticides and exclosures, to assess the contributions of different natural enemy types to distance- and density-dependent effects at seed and seedling stages. We found that distance- and density-dependent mortality caused by natural enemies was most likely at the seedling stage and was greater at higher mean annual temperatures. Conspecific negative distance- and density-dependence at the seedling stage is significantly weakened when fungicides were applied. By contrast, negative conspecific distance- and density-dependence is not a general pattern at the seed stage. High seed mass reduced distance- and density-dependent mortality at the seed stage. Seed studies excluding only large mammals found significant negative conspecific distance-dependent mortality, but exclusion of all mammals resulted in a non-significant effect of conspecifics. Our study suggests that plant pathogens are a major cause of distance- and density-dependent mortality at the seedling stage, while the impacts of herbivores on seedlings have been understudied. At the seed stage, large and small mammals, respectively, weaken and enhance negative conspecific distance-dependent mortality. Future research should identify specific agents of mortality, investigate the interactions among different enemy types and assess how global change may affect natural enemies and thus influence the strength of conspecific distance- and density-dependence.     

云南省剑川县鼠疫自然疫源地宿主媒介情况分析

了解鼠疫自然疫源地的宿主、媒介群落结构及其种群动态,为提出针对性的鼠疫防控策略与机制提供依据.云南省剑川县属于齐氏姬鼠和大绒鼠鼠疫自然疫源地的核心区,该区域小型兽类种类丰富,存在2种类型鼠疫菌,为进一步研究疫源地的演变提供了重要的现场模型.本文对剑川县1976-2019年鼠疫监测资料进行整理和分析,发现该疫源地室内共捕...     

Faunistic analysis of the fleas on small mammals in the trans-Aral Sea area

Materials on occurrence and abundance of 36 species of fleas on 17 species of small mammals are systematized. A great similarity between the faunas of ectoparasites of rodents and predators has been shown by means of special indices. The conception of parasitic field is formulated which implies the phenomenon of community of the fauna of plague vectors parasitic on its potential carriers. Some aspects of the formation of parasitic field and its possible effect the epizootic process are considered. It is established that the similarity between the faunas of fleas from different animals is ensured in this region first of all by a wide distribution of specific parasites of gerbils.     

Natural focus of leptospirosis in the rice paddies of Krasmodar Territory and the means for its eradication

OFFthe rice fields of the Krasnodar Territory the intensive epizootic of leptospirosis icterohemorrhagica can be observed in the population of Norway rats (995 animals have been examined and 102 cultures obtained) the whole year round. The highest intensity of the epizootic process is known to fall on the end of summer and the beginning of autumn (45-50% of Leptospira carriers). The natural focus of leptospirosis on the rice-growing complex is epidemiologically dangerous. The epizootic process can be suppressed by reducing the population of rats by means of poisoned baits. The alternate use of different poisons ( rotindan , brodifacum ) given in the form of paraffined briquettes has proved to be most expedient.     

Patterns in the change in the number of carriers and epizootic activity in a floodplain local natural focus of tularemia in Voronezh Province]

Prolonged study of the population of Arvicola terrestris L. in connection with tularemia epizootic among these animals showed this animal to serve as the principal carrier of tularemia infection in the Povorinsk natural focus. Epizootics proved to originate with a definite threshold count of Arvicola terrestris L.; this threshold constituted about 30% of the trapped animals. Dynamics of the epizootic activity was characterized by alterations of cycles of various duration, coursing by waves, with 2--3-year periods. Reduction of the epizootic intensity coursed during a decade in 2 waves with 3-year periods, and during a 7-year period--in one 3-year wave. During the epizootics with the character of a 2-year wave the population of the principal carrier diminished, and with a 3-year wave the count of Arvicola terrestris L. decreased during the first year, and began to increase during the second year, despite the persistence of the epizootic. Detection of regularities attending the changes in the population of the principal carrier of the infection and its connection with the epizootics permitted to make long-period prognoses of the epizootic activity and to plan antiepidemic measures in the focus.     

A computer model of plague epizootic process in the great gerbil (<Emphasis Type="Italic">Rhombomys opimus</Emphasis>) settlements: Description and test for adequacy

The spread of plague epizootics in areas with natural plague foci, including Rhombomys opimus settlements, is usually studied in the course of annual epizootiological observations. Direct studies on the structure of epizootics and parameters of their spread are labor-intensive and, therefore, rare. Nevertheless, a number of authors have performed such studies using different methods, which made it possible to accumulate a certain factual material. This material has provided a basis for a computer model of the epizootic process in R. opimus settlements with interactively adjustable parameters. Mathematically, the model is based on a probabilistic cellular automation. The model conceptually deals with the same types of settlements as in nature: settlements with acute development of the disease, settlements with a certain proportion of immune individuals among rodents, and those not affected by an epizootic and representing a reserve for its further development. The groups of colonies (microfoci) separated from each other and unevenly distributed in the working space of the model are clearly distinguished. The epizootic process in the working space of the model shows more or less ordered cyclic fluctuations, which resemble the curve of epizootic activity in nature, and advances at a rate of 150 m to 1.5 km per 1.7–2.7 months, which well agrees with parameters recorded in field experiments with isotope-tagged animals and in the course of direct observations on the epizootic process in nature Thus, the main characteristics of the model epizootic process are quantitatively and qualitatively close to its natural analogue, which is evidence that the proposed model is conceptually correct and adequate.     

Epizootic characteristic of rabies today

During the 23 year period rabies was registered in the Moscow region in 163 cases among foxes, 22 cases among racoon-like dogs, 92 cases among dogs, 54 cases among cats. In 1991-2000 ten cases of rabies were registered among other wild animal other than foxes and raccoon-like dogs (hares, hedge-hogs, polecats, badgers, hamsters, martens, rats). Under today conditions the generalized epizootological pattern of rabies is characterized by the vector "natural foci-->anthropurgic foci" with wild and domestic animals playing an alternative role in the epizootic process and the circulation of the infective agent. Wild carnivorous animals maintain natural focal infection in time and space, while all domestic animals are a direct or indirect ecological impasse and took no part in the maintenance of the infection. Foxes are the main source of infection for the animals of the anthropurgic cycle: they play a special role in the development of the epizootic situation in the region as the main reservoir and source of the causative agent of rabies as a natural focal infection. Among other wild animals, raccoon-like dogs are involved into epizootic and epidemic chains. Dogs are the main objects to be infected in the anthropurgic cycles, while cats--a progressing group of risk. During the period of 25 years a decrease in the probability of natural rabies was noted.     

Results of using the serological method of epidemiological investigation of plague foci in the Muyunkum and Eastern Kyzylkum deserts in 1978-1982

Results of serological examination of 81,853 mammals from the Muyunkum and 26,303 from the Eastern Kyzylkum deserts were compared with results of a corresponding bacteriological examination for plague. In both foci and in all phases throughout the epizootic of plague, the serological method made it possible to detect infected animals 6-10 times more frequently in comparison with the bacteriological method. The big meriones mice, i.e., the basic carriers of plague in natural foci, were found to be infected considerably more (in percentage) frequently than the meridian meriones. Differences in the reactivity of meriones to the invasion of plague microbe were observed in both foci (the indices of titres in the antigen neutralization reaction were considerably higher in the Eastern Kyzylkums). The serological method of investigation is highly informative in evaluating both the present state of epizootic activity of a plague focus and its activity in the past.     

No evidence of persistent Yersina pestis infection at prairie dog colonies in north-central Montana

Sylvatic plague is a flea-borne zoonotic disease caused by the bacterium Yersinia pestis, which can cause extensive mortality among prairie dogs (Cynomys) in western North America. It is unclear whether the plague organism persists locally among resistant host species or elsewhere following epizootics. From June to August 2002 and 2003 we collected blood and flea samples from small mammals at prairie dog colonies with a history of plague, at prairie dog colonies with no history of plague, and from off-colony sites where plague history was unknown. Blood was screened for antibody to Y. pestis by means of enzyme-linked immunosorbent assay or passive hemagglutination assay and fleas were screened for Y. pestis DNA by polymerase chain reaction. All material was negative for Y. pestis including 156 blood samples and 553 fleas from colonies with a known history of plague. This and other studies provide evidence that Y. pestis may not persist at prairie dog colonies following an epizootic.