Natural-focus infections: the key questions and new vantage points

A short history of the concept of natural focal infections is presented: the idea put forward by D. K. Zabolotny?, E. I. Pavlovski?'s teaching, 3 stages of its development. A number of fundamental questions and the modern content of the concept are considered. The natural foci of infections are a combination of surface, soil and/or water ecosystems, including the population of the causative agent of infection. In contrast to surface ecosystems, in soil and water ecosystems the hosts of the causative agents of sapronotic infections ae soil invertebrates and hydrobios, in which these agents may circulate in biocenotic trophic chains. The circulation of the causative agents in natural foci is a discrete process; the mechanisms and forms of the existence of pathogenic bacteria during seasonal and prolonged periods between epidemics is considered. Special attention is given to latent (nonculturable) forms of bacteria. The complex character of the status of the causative agents of natural focal infections is discussed.     

Regional epidemiologic characteristics of combined foci of tick-borne encephalitis, endemic rickettsioses and leptospirosis in Western Siberia

The authors carried out complex study of combined foci of infections with natural foci in Western Siberia and their reflection in human pathology. The results of serological examination of 5917 persons and of 1743 of farm animals in respect to tick-borne encephalitis, Asian tick-borne rickettsiosis, Q-rickettsiosis, and leptospiroses are analysed. Affection of the population with all the four infections in all the landscape zones under study was shown; the intensity of this affection with different infections differed. Combined natural foci of the mentioned infections were found to be widespread; epidemiological significance of such combination was unequal in different ladscapes, this depending on the ladscape characteristics of the natural foci of infections under study and of different ways of transmission of their causative agents.     

Epidemiologic situation in the quarantine of natural focal infections in the Southern Federal District

Materials on the situation in quarantine natural focal infections (anthrax, plague, tularemia, brucellosis, leptospirosis, etc.) in the Southern Federal District are presented. Experience in the provision of the epidemic safety in the above-mentioned diseases, based on the systematic surveillance on the activity of epizootological factors on the territory of the natural foci of infections, are described. The causes of the possible aggravation of the epidemiological situation in a number of nosological forms in connection with changes in natural and socio-economic factors are given. The results of the realization of regional programs, making it possible to improve the system interaction between the administrative territories, services and departments aimed at ensuring the epidemiological safety of the region, are shown.     

Combined focus of tick-borne encephalitis, tick-borne rickettsiosis and tularemia in the habitat of Haemaphysalis concinna in south central Siberia

For the first time in the Krasnoyarsk region the population Haemaphysalis concinna ticks were found to be infected with the causative agents of three natural focal tick-borne infections--tick-borne encephalitis, tick-borne rickettsiosis and tularemia. The existence of the combined natural focus of these three infections has been confirmed by epidemiological data. Ticks Dermacentor nuttalli also play a similar role in combined foci of tick-borne encephalitis and tick-borne rickettsiosis in these focal territories.     

Broader investigation into the external environment of the specific antigen of the infectious agent in epizootiological observation and study of the structure of natural foci of plague.

The possibilities of detection of the infectious agent in natural foci of plague can be expanded to some extent by using the method of search for the specific FI capsular antigen of the plague microbe in such objects of the external environment which have not yet been subjected to laboratory analysis and serological analysis in particular. Such objects include soil from the burrow and the substrate of the nest of the rodent as well as the fleas of rodents and regurgitations of birds of prey.The effectivity and suitability of examination of these objects using immuno-adsorption reactions with standard erythrocyte diagnostics (passive haemagglutination reaction, antibody neutralization reaction) were demonstrated experimentally and confirmed under field conditions in various geographical and ecological zones of the Caucasus. Thus in 1971, an earlier unknown natural focus of plague was found in the Mount Elbrus massif by means of serological analysis of the substrate of the nest and of the soil from the burrows of rodents. It can be expected that broadened serological search for the FI antigen of plague will prove useful in the study of the structure of natural foci of plague, in the reconnaissance or retrospective investigation of poorly explored territories and in the solution of some questions concerning the epizootiology of plague, such as the survival of the infectious agent in the inter-epizootic period, telluric plague, etc.     

Biocenosis of the natural foci of sapronotic infections (the results of 15-year observations)

The summarized results of original studies, carried out in 1988-2003 by scientists of the Gamaleya Research Institute of Epidemiology and Microbiology, are discussed. The part dealing with the regularity and mechanisms of the circulation of pathogenic bacteria in the biocenosis of soil and water reservoirs includes the following subjects: population and intracellular interactions with protozoa; the evaluation of different representatives of hydrobios as hosts and the transmission along trophic biocenotic chains; the effect of algae and their metabolic products on bacterial populations; the possibility of the colonization of higher plants from the soil and the subsequent infection of rodents; the variability and clonal structure of bacterial population in its interaction with protozoa and plants; the chain of Yersinia circulation in agrocenosis. The part dealing with the mechanisms of the prolonged reservation of causative agents includes such subjects as the reversible transition of bacteria into the latent (uncultivable) state in soils and water reservoirs, as well as the biological inductors of this process; the prolonged preservation of latent bacteria in the cysts of protozoa and blue-green algae; the indication of causative agents in the natural foci of plague and pseudotuberculosis. On the basis of the original investigations and the data of literature new theoretical review in the field of the natural foci and the epidemiology of sapronotic infections have been formulated.     

New findings concerning the spread of natural foci of infection in the transpolar region of eastern Siberia]

New materials are presented on the presence of the foci of anthropozoonozes in the Extreme North. For the first time there was established the existence in the subarctic tundra of the Taimyr peninsula of the arbovirus foci of the tick-borne encephalitis complex. A virus of the tick-borne encephalitis complex was isolated in 1973 from the gamasida ticks Haemogamasus ambulans Thorel. and Hirstionyssus isabellinus Oudms. and the nests of the Siberian lemming Lemmus lemmus L. This pointed to the existence in the Transpolar region of the foci or arboviruses in the nest-hole biocenoses of the lemmings outside the bird colonies. Cultures of tularemia bacilli (which proved the etiology of the epizootic among the lemmings observed in 1973 and also the presence of the lemming natural foci of tularemia and their combination with the arbovirus foci) were isolated from the lemmings at the same territory. The results of serological examination of the local population and of the animals pointed to the circulation in the Transpolar region of the causative agents of leptospirosis, toxoplasmosis, Q-fever and of the Asian tick-borne rickettsiosis.     

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.     

Infectious diseases in natural reservoirs: epidemic situation and morbidity in the Russian Federation and prophylactic measures

The analysis of morbidity in infections with natural foci in Russia for the period of 1999-2000 indicates that a rise in the number of cases of hemorrhagic fever with the renal syndrome, tick-borne encephalitis, Crimean hemorrhagic fever and West Nile fever with a high proportion of urban population among the patients is registered annually. An increase in the epizootic activity of the natural foci of plague is noted in the absence of morbidity among humans. The appearance of the outbreaks of tularemia is linked nor only with the increased activity of the natural foci, but also with the reduced coverage of the population with prophylactic immunization in endemic regions. This analysis infers that morbidity prognosis in infections with natural foci for 2001 remains unfavorable. The growth of morbidity in these infections is mainly due to the reduction of measures for controlling their vectors both is open nature and in settlements, as well as to low coverage with prophylactic immunization. Urgent complex measures which may ensure effective antiepidemic and prophylactic work for controlling infections with natural foci are presented.     

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.     

Empirical antibiotic therapy of wounds complicated by anaerobic non-clostridial infection

Antibacterial activity of 14 drugs against clinical strains of asporogenic anaerobes causing wound infections in the soft tissues i. e. Bacteroides fragilis and Bacteroides melaninogenicus as well as anaerobic gram-positive++ cocci was assayed with the method of serial dilutions in agar. It was shown that among the investigated species B. fragilis had the most marked resistance since out of the 14 drugs only 8 were sufficiently active against it i.e. carbenicillin, levomycetin, lincomycin, dioxidine, metronidazole, thinidazole, nitrazole and erythromycin. The choice of drugs for treating infections caused by B. melaninogenicus and anaerobic grampositive cocci unlike those caused by B. fragilis offered no difficulty since practically++ all the investigated drugs were highly active against the causative agents. There was observed relationship between the frequency of asporogenic anaerobes and the wound genesis. The characteristic features of the species composition connected with localization of the suppurative foci were indicated. The detected specific antimicrobial profiles of the asporogenic anaerobes causing wound infections and the peculiarity of their participation in development of purulent infections of the soft tissues provided a differential approach to empirical antibacterial therapy prior to the pathogen bacteriological investigation and availability of the antibioticograms.     

Erysipeloid on the islands of the Ohhotsk Sea. 2. Landscape types of the natural foci of erysipeloid

Cases of skin (skin-artericular) form of erysipeloid were recorded in the islands of the Sea of Okhotsk. The natural foci of the causative agent of this infection were polyhostal and polyvectoral in character. The causative agent of erysipeloid exists among the animals habitating on land and sea. Mass species of animals characteristic of the island landscape served as the sources of infection. Their four landscape types (mountaineous-taiga, of sea coast and rocks, anthropurgic settlement, and of water bodies--salt and freshwater) were preliminarily distinguished by the combination of biocenological, epidemiological, and epizootological peculiarities of natural erysipeloid foci.     

Inhibitor production, a stable feature of plague pathogen

Application of the methods developed by the author to the plague causative agent isolated in six natural plague foci provided detection of its ability to synthesize a factor inhibiting the growth of the producing strain and cultures isolated from the same focus. In the strains isolated from these foci the inhibitor presence was stable on the agar consisting of fermentative casein hydrolysate and 0.6 per cent of lithium chloride when the indicator strains were incubated under definite temperature conditions. The results of the present study and previous studies of the author, as well as the literature data suggested that the ability to synthesize the inhibitor is a stable feature of the plague causative agent.     

Some aspects of the resistance of natural foci of zoonosis infections with an example of the tick-borne encephalitis

Epidermiological material reflecting some spatio-temporal aspects of the natural foci of tick-born encephalitis resistance has been analysed. The investigation carried out can used as a base for elaboration and realisation of factor prognoses concerning natural foci of zoonosis infection.     

The 70th anniversary of E.N. Pavlovsky’s concept of natural nidality of human diseases

The concept of the natural nidality of human diseases has significantly changed during the last 70 years, but its essence is preserved. Many “new” infections with natural foci were discovered and their geographical distribution was investigated in detail, and the classification of natural foci was developed. It has been established that epidemic features of transmissible infections depend mainly on types of parasitism of insect, tick and mite vectors.     

Effects of habitat-conditioning by the damselfish Stegastes nigricans (Lacepède) on the community structure of benthic algae

We compared the community structure of benthic algae inside and outside pomacentrid damselfish (Stegastes nigricans) territories in a moat at Sesoko Island, Okinawa, Japan. S. nigricans maintained “algae farms” that were dominated by the filamentous rhodophyte, Womersleyella setacea. Species richness and biomass were higher inside damselfish territories than outside, while species diversity and evenness were higher outside. Detrended correspondence analysis (DCA) based on species composition showed that the dominance of W. setacea was maintained throughout the year in all samples collected from inside damselfish territories. The observed strong dominance of filamentous rhodophytes was consistent with the findings of most studies on damselfish territories worldwide. However, the dominance of a single species of alga and low species diversity inside the territories was in contrast to the findings of previous studies, in which the reduction of grazing pressure caused intermediate disturbance and enhanced algal species diversity. This discrepancy in algal species diversity inside the damselfish territories seems to have been caused by unique characteristics of the alga and the fish. W. setacea traps sediment, which reduces the availability of firm substrata for attachment and inhibits the recruitment of some algae. Moreover, S. nigricans “weeds” indigestible calcareous and thicker algae. The algal assemblage outside damselfish territories varied among samples, and included mat-forming cyanophytes (Calothrix aeruginosa and Calothrix codicola), a prostrate laminar phaeophyte (Padina sp.), thin and small-scaled algae (Cladophora sp. and Feldmannia indica), finely branched filamentous rhodophytes (Taenioma perpusillum and Herposiphonia obscura), and a coarsely branched rhodophyte (Gelidiopsis variabilis).

We placed artificial slate plates inside and outside damselfish territories, and showed that the W. setacea inside territories gradually increased in biomass, reaching the same levels of biomass and dominance as W. setacea on natural substrata. Outside the territories, the algal assemblage underwent succession from early colonizers, i.e., thin and small-scaled algae, to grazing-resistant algae such as mat-forming cyanophytes and prostrate laminar Padina sp. Under heavy grazing, the flora outside the territories was composed of early colonizers, grazing-resistant algae, and scattered erect algae that had probably escaped grazing by chance.

Our findings suggest that sediment trapped by the turf of W. setacea inhibited recruitment of some algae, and that moderate cropping and selective weeding by S. nigricans excluded grazing-resistant algae and prevented early colonizers and competitively superior algae from out-competing W. setacea. Consequently, low species diversity and a high-biomass “farm” suitable for harvesting was maintained.     

Quantitative motion analysis of subchromosomal foci in living cells using four-dimensional microscopy

The motion of subchromosomal foci and of whole chromosome territories in live human cell nuclei was investigated in four-dimensional space-time images. Visualization of subchromosomal foci was achieved by incorporating Cy3-dUTP into the nuclear DNA of two different cell types after microinjection. A subsequent segregation of the labeled cell nuclei led to the presence of only a few labeled chromosome territories on a background of nonlabeled chromatin (. Hum. Genet. 102:241-251). This procedure yielded many distinct signals in a given cell nucleus. Motion analysis in four-dimensional space-time images was performed using single-particle tracking and a statistical approach to the detection of a possible directional motion of foci relative to the center of mass of a chromosome territory. The accuracy of the analysis was tested using simulated data sets that closely mirrored the experimental setup and using microparticles of known size. Application of the analysis tools to experimental data showed that mutual diffusion-like movements between foci located on different chromosomes were more pronounced than inside the territories. In the time range observed, movements of individual foci could best be described by a random diffusion process. The statistical test for joint directed motion of several foci inside chromosome territories revealed that foci occasionally switched from random to directional motion inside the territories.     

Characterization of the natural foci of Congo-Crimean hemorrhagic fever on the territory of Ukraine

The natural foci of the Congo-Crimean hemorrhagic fever (CCHF) in Ukraine were characterized by their geographical factors. The circulation of CCHF virus was found to occur mainly in forest and forest-steppe zones irrespective of the location of administrative regions. The territories found to be most favorable for the prolonged existence of the focus of CCHF were those having high humidity. The possibility of using geoinformation technologies for the correction of the boundaries of natural foci, the evaluation of the influence of geographical factors on the circulation of the virus was shown.     

Sanitary control of the territory: data bases on the spread of some quarantine infections

The data bases (DB) on the spread of plague, yellow fever and contagious virus hemorrhagic fevers (CVHF) in foreign countries have been created. These DB contain information on the main international air and sea ports and their relationships with natural focal territories. The data base "Sanitary control. Yellow fever" contains information on different species serving as vectors for yellow fever virus. Information on the circulation of the causative agents of Ebola fever, Lassa fever and Marburg disease in African countries has been introduced into DB, the differentiation of countries by the degree of the potential danger of the CVHF spread has been made.     

Epidemiological surveillance on natural-borne infections in the Ulyanovsk region

The analysis of natural foci of haemorrhagic fever with renal syndrome (HFRS) and tick-borne borreliosis on the territory of the Ulyanovsk region is presented. Reduced rat control interventions result in a wide spread of these and other infections with natural focality. Monitoring of natural foci of HFRS, tick-borne borreliosis and arbovirus infections, their typing and determination of main reservoirs are the most promising among epidemiological surveillance methods.