Natural Plague Foci Research Articles

The Dominance Indices and the Probability to Involve Different Fleas Types in Epizootic Diseases on the Example of Central-Caucasian High-Mountain Natural Plague Focus

The paper attempts to use an indicator of the number of fleas of different species in the natural focus of the plague to assess the intensity of epizootics. The correlation between the number of fleas of seven species and the number of isolated strains of plague microbe is established. It is shown for small species to be more often involved in epizootics during their intensive course, which corresponded to the first period of the focus activity. In the second period characterized the tendency to decrease the share of small species in the epizootic process. The third period demonstrated a significant difference with the first two previous ones. The detection insamples of field material of infected secondary carriers of these species or random carriers was indirect evidence of intense epizootics.

Current Status of the Sari-Dzhas Natural Focus of Plague, Kyrgyzstan: Epizootic Activity and Marmot Population.

The Sari-Dzhas natural mountain focus of plague with an area of 5000 sq. km is located mainly in Kyrgyzstan. This enzootic area belongs to a group of Tien-Shan mountain plague foci and crosses the boundaries of Kazakhstan, Kyrgyzstan, and China. After collapse of Soviet Union, this area was not investigated fully, thence we have estimated current status of hosts and vectors comparing to 1977 in the Sari-Dzhas focus. For period 1977-2014, the number of the gray marmot (Marmota baibacina) as main host of plague has decreased twice due to regular chemical suppression of focal area, but now there is a tendency for population recovery. If negative impact of human activity (hunting, livestock, and tourism) will be minimized, the population density should rise in the near future, related to high reproduction score of animals. Significant increase of number of narrow-skulled vole (Microtus gregalis) observed on focus area in 1977-2017 can effort a risk of pathogen transmission in cross-populations of marmots provided by recovery of vector number between different hosts. For whole observation period in the Sari-Dzhas focus were described 33 species of marmot fleas with dominated Oropsylla silantiewi (67% from whole amount of fleas) and Radinopsilla li ventricosa (6.5%). Deep dustation of marmot burrows by 10% dichlorodiphenyltrichloroethane (DDT) conducted in 1980s caused significant decrease of ectoparasite abundance: the number of specific fleas is strongly diminished, while recovery of ticks and lice number is faster. At the same time, Yersinia pestis constantly circulates in the focal area, which is comfortable for interacting of human populations and pathogen hosts. Last plague epizootic was recorded in 1983 and recent outbreaks among gray marmot and its vectors with varying intensity are registered again starting from 2012. Thus, the Sari-Dzhas natural plague focus remains active with all links of plague epizootic cycle (marmot-vector-rodent) and needs strong monitoring every year.

Taxonomic Position of Entomoparasitic Nematodes Isolated from Fleas in Gorno-Altai High-Mountain Natural Plague Focus

Objective of the study was to investigate entomoparasitic nematodes from rodent fleas, collected in Gorno-Altai high-mountain natural plague focus in 2016–2017, with identification of their taxonomic status. Materials and methods. Given are the results of morphological and genetic analysis of entomoparasitic nematodes – parasites of fleas Amphipsylla primaris primaris living on flat-headed high-mountain voles Alticola strelzovi, fleas Rhadinopsylla li transbaicalica of Daurian pika Ochotona dauurica, fleas Rhadinopsylla dahurica, collected at the burrows of the rodents. Results and conclusions. Identified have been nucleotide sequences of ITS2 spacer region of ribosomal operon in entomoparasitic nematodes of three flea species: Amphipsylla primaris primaris, Rhadinopsylla li transbaicalica, and Rhadinopsylla dahurica. Based on comparative phylogenetic analysis and identified high percentage of homology of the stated nucleotide sequences (92–99 %), appurtenance to Rubzovinema spp. species and close relation to earlier proposed by us multi-host species Rubzovinema polyxenica from C. tesquorum, A. rossica, and C. secundus fleas from Volga-Ural steppe plague focus has been established. For the first time ever separate branch of evolution of entomoparasitic nematodes – flea parasites, represented by Rubzovinema ssp., has been identified. Determined has been wide spread of Rubzovinema ssp. nematodes in biocenoses of steppe zone of Russia across Precaspian territory and Altai Mountains.

Current Epizootic Condition of Natural Plague Foci in Kyrgyz Republic and Measures Aimed at Provision of Epidemiological Welfare as regards Plague

Objective of the study is to characterize the mountain plague foci in Tien Shan and Pamir-Alai, to assess the results of the performed field disinsection activities, to describe the current epizootic condition of natural foci in Kyrgyz Republic and measures aimed at provision of epidemiological welfare as regards plague. Materials and methods. Archival epizootic and epidemiological data from the Republican Center of Quarantine and Particularly Dangerous Infections, Ministry of Health of Kyrgyz Republic, as well as copyright author’s materials were used for the analysis. Results and Conclusions. It is noted that following sanitation activities in 1971–1989, using deep disinsection of marmot burrows, epizootic activity of Tien Shan and Alai natural foci significantly decreased, up to long inter-epizootic periods. In the light of revitalization of high-mountain plague foci in Kyrgyz Republic, epizootiological monitoring of enzootic territories has been considerably strengthened, control over the state of populations of main agent carriers and vectors has been improved. In order to lower the risk of infection, 1750 km2 of the focal territories were treated twice, using deep disinsection of marmot burrows applying ecologically safe insecticides, in particular “Absolute-dust”.

Mongolian Part of the Trans-Boundary Sailugem Natural Plague Focus in 2017. Communication 2. Modern Epidemiological Risks

Objective – to study the current epidemiological risks at plague enzootic frontier territory of the Bayan-Ulgy aimag of Mongolia. Materials and methods. Epidemiological analysis was performed according to the reporting documentation of the National Centre of Zoonotic Infections in Mongolia, results of anonymous questioning of 179 residents of the Bayan-Ulgy aimag of Mongolia, materials of the Department of Health of the Bayan-Ulgy aimag, the Aimag Centre of Zoonotic Infections and the Administration of the Aimag Governor. Results and discussion. Plague was first registered in the Bayan-Ulgy aimag in 1989. The total of 9 patients with plague and 4 lethal outcomes were revealed. In all cases marmots were an infection source, the infection occurred in the process of cutting the carcasses. The majority of the plague patients had bubonic form of plague. All patients were men aged 13 to 34 years. Public inquiry showed that 21,8 % of population considered meat of marmots as a delicacy, 54 % – hunted for the animals, 25,7 % – consumed uncooked organs of marmots as a folk remedy, 19,5 % – participated in cutting of marmot carcasses. Results of the inquiry indicated that a marmot was an object of active hunting for local population. Analysis of epizootic activity of the transboundary Sailugem natural plague focus, modern social and economic conditions in the Bayan-Ulgy aimag has showed that in this territory epidemic risks have shaped and act at present. They can be divided into two groups: epidemic risks capable to cause human sporadic plague cases and epidemic risks leading to anthropozoonotic plague dissemination among the population and exportation of Yersinia pestis beyond the limits of enzootic territories. Effective interaction of anti-epidemic Institutions of Mongolia and Russia and also the Agencies and Institutions of the executive power of all levels permits to counteract these risks.

Relationship of the Representatives of Eight Genera of Siphonaptera Order and Yersinia Pestis from Tuva Natural Plague Focus

Mutual relations of Yersinia pestis and fleas are a necessary condition to estimation the role of carriers in maintenance of the causative agent circulation. Objective – the comparative analysis of frequency of «conglomerate» and «block» formations by Y. pestis in fleas parasitizing on the main and minor carriers in the Tuva natural focus. Materials and methods. Results of experiments with representatives of eight genera of Siphonaptera order and Y. pestis subsp. pestis from the Tuva focus were analyzed. Mammals with various epizootological roles in the focus were used as flea fooders. Frequency of «block» and bacterial «conglomerate» formations and death of the infected insects was estimated. Results and discussion. The highest level of block formation was observed in Citellophilus tesquorum altaicus, Frontopsylla elatoides, Neopsylla mana, Oropsylla alaskensis, Rhadinopsylla li transbaicalica – parasites of the basic carrier (Spermophilus undulates). Formation of «conglomerates» was more often revealed in F. hetera, Paradoxopsyllus scalonae, P. scorodumovi, P. dashidorzhii, Amphipsylla primaris – ectoparasites of the minor carriers (Ochotona pallasi, Alticola strelzovi). Positive connection between frequency of Y. pestis conglomerate formations in fleas and their death rate was detected. Maximal death rate of the carrier was observed at high degree of Y. pestis aggregation. It was supposed that fleas of the basic carrier participated in a greater degree in Y. pestis distribution and ectoparasites of the secondary carriers – in its persistence.

Mongolian Part of the Transboundary Sailugem Natural Plague Focus in 2017. Communication 1. Epizootic condition

Objective – estimation of current epizootic condition of Mongolian part of transboundary Sailugem natural plague focus. Materials and methods . Epizootiological survey was performed for the area of 2335 km 2 , 277 mammals and 516 ectoparasites were investigated for plague. Results and conclusions . Eight Yersinia pestis subsp. pestis strains were isolated, including 7 strains – from grey marmots (6 – from the remains of meals of predatory birds, 1 from a corpse) and 1 – from long-tailed souslik (corpse). Y. pestis DNA was detected in 52 objects. Serological samples showed 40 positive results. Epizootic manifestations, confirmed by isolation of Y. pestis cultures, detection of plague microbe DNA, and positive serological results, were observed across the area of 1611 km 2 covering 69 % of the inspected territory. Epizootic results indicated high infection rate of mass mammal species and first of all grey marmots. The data demonstrated that the extended plague epizooty caused by Y. pestis of the main subspecies occurred in the inspected territory in the carrier settlements. For the first time the circulation of Y. pestis subsp. pestis was registered in the Mongolian part of the transboundary Sailugem focus.

Epizootic Activity of Natural Plague Foci of the Russian Federation in 2008–2017 and Forecast for 2018

Epizootic Activity of Natural Plague Foci of the Russian Federation in 2008–2017 and Forecast for 2018

EVALUATION OF HUMORAL AND CELLULAR IMMUNITY LEVEL AMONG PERSONS LIVING IN THE CASPIAN NATURAL SANDY FOCUS TERRITORY AFTER ANTI-PLAGUE REVACCINATION

In view of increasing epidemic danger potential of some natural plague foci and performing measures to provide specific prevention of this infection, it becomes necessary to carefully monitor the state of immunity in vaccinated (revaccinated) individuals. The aim of the study was to assess humoral and cellular immunity levels in the persons after repeated anti-plague revaccination performed for appropriate epidemiological indications. Evaluation of immune responses to anti-plague revaccination was carried out according to studies of blood samples from 20 people aged 24 to 53 years living in the Caspian sandy natural plague focus located at the territory in Kalmykia Republic. Specific antibody titers to the F1 antigen of plague microbe were assessed in blood serum by immunoassay testing using an “ELISA-AT-F1 YERSINIA PESTIS” test system (Russian Research Anti-Plague Institute “Microbe”, Russia), along with spontaneous and concanavalin A-induced production of different cytokines, i.e., IFNγ, TNFα, IL-4, IL-10 (Vector-Best, Russia), IL-17A (Bender Medsystems, Austria). The studies were performed before vaccination, and 1, 6, 12 month after the booster vaccination. The results of the study indicate that immunological reconstitution after revaccination with live plague vaccine occurs occurred mostly according to mixed Th1/Th2 type. Detection of antibodies to the F1 specific plague microbe antigen before and 1 month after revaccination (65 and 85%, respectively) was indicative of development of humoral response. The most informative cytokine markers (IFNγ and TNFα) for evaluation of an anti-plague cellular immune response have been identified. The threefold increase in IFNγ induced production before revaccination indicates to initial immunological competence of all the examined individuals. A high correlation between TNFα and other cytokine levels was determined. The fact of high correlation for the studied cytokines (TNFα, IFNγ, IL-10) indicated to a synchronism in the immunocompetent T helper cell reaction. By measuring the levels of spontaneous and induced cytokine production levels, one may indirectly judge on degree of anti-plague cell immunity in humans.

THE USE OF UNMANNED AERIAL VEHICLE TO IMPROVE THE EFFICIENCY OF NATURE PLAGUE FOCUS MONITORING

New technologies based on remote sensing, has been actively developing now for the increasing the effectiveness of nature plague foci monitoring. The unmanned aerial vehicle (UAV) «GeoScan–101» was used for monitoring and for orthophoto creating. The monitoring was carried out at Caspian nature plague focus on a stationary square 4 ha. The accounting of rodents’ holes had been implemented previously. Gerbils Meriones tamariscinus is the host of plague microbe in the Caspian natural plague focus. The monitoring using UAV allows identifying 78,26 % of Meriones tamariscinus holes as well as Microtus socialis and Ellobius talpinus. The comprehensive using remote sensing from space and data from drone (a high-resolution picture in real time) for elaboration data of remote sensing allows increasing the effectiveness of nature plague foci survey, where the hosts have the holes small diameter: the gerbils' genus Meriones and the voles’ genus Microtus.

Phenotypic and Molecular Genetic Characteristics of Yersinia pestis at an Emerging Natural Plague Focus, Junggar Basin, China.

The 15th natural plague focus in China, the Junggar Basin plague focus, is located near an important communication route connecting China and Central Asia and was discovered after 2005. To characterize the phenotypic and genetic diversity of the Yersinia pestis population in this newly established focus, we collected 25 Y. pestis strains from six counties across Junggar Basin in 2005-2006, and determined their biochemical features and genotypes based on multiple-locus variable number of tandem repeats analysis and clustered regularly interspaced short palindromic repeats analysis. We inferred the phylogenetic positions and possible sources of the Junggar strains by comparing their genotypes with the genetic diversity for known representative Y. pestis strains. Our results indicate that the major genotype of Junggar strains belongs to 2.MED1, a lineage of biovar Medievalis with identical biochemical characters and high virulence in mice. Although share a similar ecology, the 2.MED1 in Junggar Basin are not descended from known strains in the neighboring Central Asian Desert plague foci. Therefore, the emergence of the Junggar Basin plague focus is not attributable to the recent clonal spread of Y. pestis from Central Asia. We also identified two distinct minor genotypes in Junggar Basin, one of which clusters genetically with the 0.ANT1 strains of the Tianshan Mountain natural plague focus and another belongs to a 1.IN lineage not previously reported. Our study clarifies the phenotypic and genetic characters of Junggar Y. pestis strains. These findings extend our knowledge of the population diversity of Y. pestis and will facilitate future plague surveillance and prevention in Junggar Basin and adjacent regions.

СОСТОЯНИЕ ЧИСЛЕННОСТИ ВТОРОСТЕПЕННЫХ НОСИТЕЛЕЙ В ПРИРОДНЫХ ОЧАГАХ ЧУМЫ СЕВЕРНОГО КАВКАЗА ЗА ПЕРИОД 2012 – 2017 гг.

СОСТОЯНИЕ ЧИСЛЕННОСТИ ВТОРОСТЕПЕННЫХ НОСИТЕЛЕЙ В ПРИРОДНЫХ ОЧАГАХ ЧУМЫ СЕВЕРНОГО КАВКАЗА ЗА ПЕРИОД 2012 – 2017 гг.

Plague: Recognition, Treatment, and Prevention.

Plague is caused by Yersinia pestis and is not commonly encountered in clinics, although natural plague foci are widely distributed around the world. Y. pestis has been listed as a category A bioterrorism agent. A neglected diagnosis will cause severe consequences. Therefore, this minireview briefly introduces the current understanding on Y. pestis and then focuses on practical aspects of plague, including clinical manifestations, diagnosis, treatment, and prevention, to alert clinicians about this notorious disease.

Study of Interactions of Microscopic Fungi Isolated from Burrow Microbiotopes of Great Gerbil and Little Souslik with Plague Agent and its Vectors

At present there is strong evidence of the long-term persistence of Yersinia pestis in soil during interepizootic period in nonculturable and L-forms of bacteria. This information helps to reveal the mechanisms of emergence, establishment and extinction of plague foci. Deciphering causes of transformation of plague microbe in rodent burrows is possible only under condition of detailed study of biocenotic relations of plague causative agent with each of the multiple biocenosis components, including microorganisms -permanent inhabitants of the burrow microbiotopes in natural plague foci. Purpose of the study: Study of interactions of microscopic fungi-micromycetes iso-lated from burrow microbiotopes of great gerbil and little souslik in the Ural-Emba interfluve and in Nogai steppe with plague agent and its vectors. Materials and methods: The effect of 74 micromycete species, isolated in natural plague foci, on Yersinia pestis virulent strains was studied in vitro and in vivo (in organisms of X. skrjabini fleas). In the experiments in vitro fungi metabolites were applied on the lawns of Y. pestis test-cultures with subsequent recording of the size of lysed zones. Fleas were challenged in tubes with filtering-paper strips impregnated by fungal cultural liquid and then LT100 value was calculated. In the experiments in vivo fungus conidia were applied on the surface of insect cuticle; flea challenging with plague was carried out on agonizing white mice infected by plague microbe. Insect challenge with plague and fungal conidia was alternated in different succession. Results and discussion: Of 74 micromycete strains 78.4% produced antagonistic effect in relation to 1-5 Y. pestis strains. Ashergillus versicolor, A. clavatus, A. sulfereus, Mucor racematus, Penicillium baarnensens, P. sp. relative to P. charlesii, P. sp. relative to P. martensii, P. insectus, P. chrysogenum fungi induced growth suppression of all five test strains of Y. pestis. High antibiotic activity of fungi metabolites was accompanied by insecticidal activity against Xenopsylla skrjabini fleas. Microscopic fungi P. funiculosum, P. cyclopium, P. chrisogenum, P. charlesii. P. canescens, A. versicolor induced 100% flea death on 4-6 day. As a result of insect pretreatment by conidia of P. funiculosum with subsequent challenging with plague microbe block formation in fleas decreased 14 times, and the number of Y. pestis cells after 12 days was 25-33 times less independent of succession, in which insects were challenged with microorganisms. Conclusion. It is supposed that micromycetes could play an important role in natural plague foci, adjusting epizootic activity of plague vectors and causative agent.

Application of GIS Technologies for Determination of Boundaries and Area of Epizootic Regions within Natural Plague Foci

Spatial indicators of epizooties in natural plague foci are used for justified planning and carrying out measures on epidemiological welfare provision for the population residing in enzootic territories. Plague affected regions are identified by real geographical coordinates of epizootic sites. Objective of the study is to develop numerical methods for determination of boundaries and area of epizootic regions according to the results of epizootiological monitoring. Materials and methods. Utilized are the digital maps of the natural plague foci, the data on epizootic points, and computer software. Results and conclusions. Buffer zones in the form of circumference of 5 km radius were established around each epizootic point with the help of computer application “ArcGIS 10.x” as a counterpart of circular extrapolation method. Resultant epizootic region over a certain season was generated by several overlapping circumferences. Evaluated were the area and extension of the region, as well as the presence of epidemiologically significant objects within its bonds. Actual positioning of the region, visualized on the focus map, is used for specified task assignment as regards carrying out of various preventive measures in this or that part of the area.

Outbreak of Pneumonic Plague in 2017 on Madagascar

The causes of emergence and development of pneumonic plague outbreak in 2017 on Madagascar were analyzed. Summarized were the literature data, characterizing the spatial and biocoenotic structure of natural plague focus on Madagascar, assessed were the risk factors of plague infection among rural and urban population of the island, as well as the properties of Yersinia pestis strains isolated there in the XX century. It is substantiated that the distinctive type of plague outbreaks on Madagascar is a rural one. It is demonstrated that one of the main causes of wide spread of plague in 2017 is importation of the infection from central regions of the Republic of Madagascar into big cities with further formation of multiple epidemic foci. Confirmed was the circulation of Y. pestis strains that belong to the third branch of irradiation of oriental biovar (1.ORI3). Discussed are the issues of diagnostics and treatment of plague in epidemic foci in the territory of the Republic of Madagascar. The evidence is provided to the fact that the plague outbreak in 2017 on Madagascar is the consequence of a lower surveillance level, first and foremost undervaluation of specific and non-specific prophylaxis capacities regarding this infection.

Epidemics and risk factors of plague in Junggar Basin, Xinjiang Uygur Autonomous Region, 2007-2016

Objective: To explore the epidemic situation of animal plague in Junggar Basin natural plague foci. Methods: Data on epidemics of plague and on population involved, as well as results on antibodies and pathogens, were analyzed. Samples on animals and vectors were collected from 18 counties in Junggar Basin plague natural foci between 2007 and 2016. Results: The density of Rhombomys (R.) opimus was temporally fluctuant, from 2.1/hm(2) to 22.6/hm(2) respectively. However, the spatial distribution appeared asymmetrical, with the highest seen in Kelamayi and Wumuqi-midong counties, as 14.2/hm(2) and 13.0/hm(2) respectively. Rates of capture on nocturnal rodents were from 4.2% to 10.1%, with the highest rate as 10.1% in 2014. Meriones meridianus appeared the dominant species in the nocturnal community of rodents, which accounted for 81.9%. Regarding the spatial and temporal distributions, rates of R. opimus with fleas appeared fluctuant, with an average rate as 90.7% and the average total flea index was 10.44. In flea community of R. opimus, Xenopsylla (X.) skrjabini was found the dominant species, popular in distribution and accounted for 47.8%. The average rate of nocturnal rodents with flea was 20.2%, with total flea index as 1.20 and the dominant fleas were X. conformis conformis and Nosopsyllus laeviceps. A total of 13 species with 9 087 serum samples from rodents were detected as having Y. pestis antibody by IHA, with 617 positive samples. Of them, the positive rate of having R. opimus appeared the highest (9.4%), followed by D. sagitta (1.1%). Spatially, two clustered areas were found, with one in the eastern Junggar Basin from Changji to Mulei county, with the antibody positive rates of R. opimus as 14.3%. The other one was in the central area of Junggar Basin, including Kelamayi, Shawan and Wusu counties, with the antibody positive rate as 13.6%. The prevalence of plague on R. opimus was fluctuant, with the lowest seen in 2008, with the average antibody positive rate of R. opimus as 1.0% and the highest as 19.3% in 2013. A total of 18 strains were isolated from 2007 to 2016. However, most of the strains were isolated from R. opimus and parasitic fleas, accounted for 8/9, in Kelamayi, Wulumuqi-midong and Jimusaer, respectively. Conclusions: Complex ecosystem was seen in the Junggar Basin natural plague foci, with the multiple composition of species and different community structure of hosts and vectors, plus the flustering prevalence. Animal plague was seen in the whole region with succession of the plague nature foci. Passive transmission of plague between human beings and animals through close contacts was seen which was driven by economic benefits to some degree.

Three Genetically Different Lineages of Yersinia pestis subsp. Microtus bv. Caucasica (0.PE2) Strains Circulate among Common Voles in Natural Plague Foci in the Caucasus

Gram-negative bacteria Y. pestis subsp. pestis of 0.ANT-4.ANT, 1.ORI, and 2.MED SNP types are the cause of numerous epidemic outbreaks, epidemics, and three plague pandemics, claiming hundreds of millions of human lives. At the same time, strains of the microtus subspecies that belong to the 0.PE SNP type circulating in populations of different species of voles (Microtus spp.) are able to cause only extremely rare human infections that are not transmitted from person to person. It is suggested that the clinical form of the infection can develop only in individuals with impaired immune status. Strains of Y. pestis bv. caucasica (0.PE2), one of the most ancient phylogenetic groups of subsp. microtus, are isolated on the territory of the following natural foci: the Transcaucasian highland (including the Leninakan (4), Pre-Sevan (5), and Zanzegur- Karabakh (6)) mesofoci and the Dagestan-highland (39). In addition to the enumerated areas, similar strains of Y. pestis are isolated in the territories of the Pre-Araks focus (7) bordering the Transcaucasian highland one. Previously, we showed that passport data on the phenotypic differences of strains of the biovar caucasica, isolated from different foci, corresponded to their MLVA25, CRISPR, and DFR genotypes. In the present work, a comparative analysis of the clustering ability of MLVA25- and CRISPR-typing methods with the “gold standard” of phylogenetic studies—SNP typing—has been conducted on 21 strains of Y. pestis subsp. microtus bv. caucasica (0.PE2). The analysis of the obtained results confirms the existence of three clonal clusters of strains corresponding to the natural plague foci—39, 4, and the group of foci 5–7. Only the SNP-typing method made it possible to separate branch of focus 5 isolates from a group of strains isolated in foci 5–7. In addition, this method made it possible to reveal a greater genetic heterogeneity of strains from focus 39, in contrast to the strains of foci 4–7. When analyzing the genomes of Y. pestis strains isolated in the territory of focus 39, a deletion (~20 kb) was detected in the CRISPR region of the Ypb locus. The absence of this locus can serve as a marker for the determination of a given population of Y. pestis strains.

Temporal and spatial distribution characteristics in the natural plague foci of Chinese Mongolian gerbils based on spatial autocorrelation

BackgroundThe nest flea index of Meriones unguiculatus is a critical indicator for the prevention and control of plague, which can be used not only to detect the spatial and temporal distributions of Meriones unguiculatus, but also to reveal its cluster rule. This research detected the temporal and spatial distribution characteristics of the plague natural foci of Mongolian gerbils by body flea index from 2005 to 2014, in order to predict plague outbreaks.MethodsGlobal spatial autocorrelation was used to describe the entire spatial distribution pattern of the body flea index in the natural plague foci of typical Chinese Mongolian gerbils. Cluster and outlier analysis and hot spot analysis were also used to detect the intensity of clusters based on geographic information system methods. The quantity of M. unguiculatus nest fleas in the sentinel surveillance sites from 2005 to 2014 and host density data of the study area from 2005 to 2010 used in this study were provided by Chinese Center for Disease Control and Prevention.ResultsThe epidemic focus regions of the Mongolian gerbils remain the same as the hot spot regions relating to the body flea index. High clustering areas possess a similar pattern as the distribution pattern of the body flea index indicating that the transmission risk of plague is relatively high. In terms of time series, the area of the epidemic focus gradually increased from 2005 to 2007, declined rapidly in 2008 and 2009, and then decreased slowly and began trending towards stability from 2009 to 2014. For the spatial change, the epidemic focus regions began moving northward from the southwest epidemic focus of the Mongolian gerbils from 2005 to 2007, and then moved from north to south in 2007 and 2008.ConclusionsThe body flea index of Chinese gerbil foci reveals significant spatial and temporal aggregation characteristics through the employing of spatial autocorrelation. The diversity of temporary and spatial distribution is mainly affected by seasonal variation, the human activity and natural factors.

Dynamics of F1 antibody responses to Yersinia pestis infection in Rhombomys opimus

Objective: To observe the dynamics of antibody response in great gerbils infected with Yersinia pestis in experiment. Method: A total of 211 great gerbils were captured in the southern margin of plague natural focus of Junggar Basin of the Xinjiang Uygur Autonomous Region in 2011. Among them, there were 167 great gerbils without infection of Y. pestis and 44 great gerbils infected by Y.pestis. Y.pestis No. 2504 was employed for this experimental strain, which was strong toxic strain with negativity in the reduction experiment of nitrate. 35 great gerbils without the infection of Y. pestis were divided randomly and averagely into 7 groups including 6 experimental groups and 1 control group. Great gerbils in the 1st to 6th experimental groups were exposed first with 1 × 10(6)-1 × 10(11) CFU/ml of bacterial fluid with 10 times of gradient dilution; groin areas of great gerbils in the control group were injected subcutaneously with physiological saline; and the amount of infection was all 1 ml. 17 great gerbils infected with Y. pestis and the first detection of F1-antibody titer in 1∶256-1∶4 096 were grouped according to F1-antibody titer: group 1∶4 096 (n=4), group 1∶2 048 (n=4), group 1∶1 024 (n=3), group 1∶512 (n=3) and group 1∶256 (n=3); and blood in caudal regions was collected in asepsis for the detection of F1-antibody, with a total of 5 times. 9 great gerbils which were selected from the remaining great gerbils infected with Y. pestis and detected F1-antibody negative 2 times were exposed 1×10(6) CFU/ml of bacterial fluid for the second infection, with the amount of infection being 1 ml. Blood in caudal regions of great gerbils after the first and second infection were collected for the detection of plague F1-antibody on the 3rd, 5th, 7th, 15th, 30th, 60th, 90th and 120th day after infection. Declined regression models for great gerbils' antibodies were established with unary linear regression equation; declined change diagrams for the antibodies were drawn to observe the declined F1-antibody after great gerbils were exposed to Y. pestis. Results: In great gerbils with the first infection of Y. pestis, antibodies were detected in the 1 × 10(6)-1 × 10(8) CFU/ml of group on the 30th, 15th and 15th day, respectively; the positive rates of antibody were 1/4, 3/4 and 4/5, respectively; the group 1×10(7) and 1× 10(8) CFU/ml reached to the highest antibody titer with 1∶256 on the 120th day; antibodies were revealed in the group 1×10(9), 1×10(10) and 1×10(11) CFU/ml from the 5th to 7th day when the seroconversion of all antibodies was observed; group 1×10(11) CFU/ml reached to the highest antibody titer on the 120th day with 1∶4 096. In the great gerbils with the second exposure to Y.pestis, positive antibodies were detected on the 3rd day with the positive rate being 2/9; and the highest antibody titer with 1∶2 048 was noted on the 90th day. Unary linear regression equation of declined F1 antibody of great gerbils was y=0.045x- 0.321 (F=115.40, P< 0.001), and the shortest duration for F1-antibody titer declining from 1∶4 096 to 0 was 140 d and the longest duration 200 d. Conclusion: Great gerbils infected with the high concentration of Y. pestis fluid show shorter duration in producing F1-antibody, the antibody positive rate is also higher, and the highest antibody titer can reach 1∶4 096. The great gerbils could hold the plague F1 antibodies for a long time which was about 140 to 200 days from the highest titer.