Plague Foci Research Articles

The origin and worldwide expansion of the plague agent Yersinia pestis: The isolation factor

Two consecutive stages of complete isolation were identified in the speciation of the plague-causing bacterium Yersinia pestis: (1) primary spatial ecological isolation was responsible for one-way migration of bacterial cells from the ancestor Yersinia pseudotuberculosis O:1b population into a transitional recurring pseudopopulation (group, clone), which gave rise to the new Yersinia pestis species in the host-parasite system of the Mongolian tarbagan marmot (Marmota sibirica) and the Oropsylla silantiewi flea; (2) pesticin synthesis and antagonistic pleiotropy effects resulted in genetic and biochemical isolation within the transient population. These two stages of complete isolation had a macroevolutionary effect: the formerly saprozoonotic microbe adopted a new lifestyle (adaptive zone) of an obligate blood parasite transmitted by fleas. Three further stages of intraspecies isolation included (1) isolation in the course of natural Yersinia pestis spread from Mongolian tarbagan marmot populations into other Asian populations of rodents and pikas, (2) isolation in the course of worldwide expansion of the plague agent during pandemics with subsequent formation of synanthropic (rat) foci, and (3) isolation in secondary natural plague foci derived from synanthropic rat foci in Africa and Americas. The last three stages of incomplete isolation had a microevolutionary effect of intraspeci? cradiation into different rodent (pika)-flea host-parasite systems.

Analysis of diversity and identification of the genovariants of plague agent strains from Mongolian foci

The genetic diversity of Yersinia pestis strains from the Mongolian natural plague foci has been investigated. A total of 32 strains isolated from western, eastern, and central aimaks, as well as from the territory of the Gobi region, have been studied. Twenty-four strains belong to the main Y. pestis subspecies, while eight belong to other subspecies. There is only one strain of biovar medievalis (genovariant 2.MED1) among the strains of the main subspecies, while the rest of the subspecies belong to the biovar antiqua. Biovar antiqua strains are split into three groups. Strains from the eastern part of the country were classified as genovariant 2.ANT3, and those from the western and central regions were classified as genovariant 3.ANT2, which was endemic for Mongolia. One strain from the Bayan-Ulegeiskii aimak had the rare genovariant 4.ANT. None of the strains of the biovar antiqua belonged to its ancient 0.ANT branch, which is inconsistent with the commonly accepted idea that ancient marmot's plague agent race originates from Mongolia. Six out of eight strains of the minor subspecies belonged to the ulegeica subspecies, which are endemic to Mongolia, one strain belonged to the microtus group, and the last belonged to a previously uncharacterized variant of the minor subspecies.

The trophic responses of two different rodent-vector-plague systems to climate change.

Plague, the causative agent of three devastating pandemics in history, is currently a re-emerging disease, probably due to climate change and other anthropogenic changes. Without understanding the response of plague systems to anthropogenic or climate changes in their trophic web, it is unfeasible to effectively predict years with high risks of plague outbreak, hampering our ability for effective prevention and control of the disease. Here, by using surveillance data, we apply structural equation modelling to reveal the drivers of plague prevalence in two very different rodent systems: those of the solitary Daurian ground squirrel and the social Mongolian gerbil. We show that plague prevalence in the Daurian ground squirrel is not detectably related to its trophic web, and that therefore surveillance efforts should focus on detecting plague directly in this ecosystem. On the other hand, plague in the Mongolian gerbil is strongly embedded in a complex, yet understandable trophic web of climate, vegetation, and rodent and flea densities, making the ecosystem suitable for more sophisticated low-cost surveillance practices, such as remote sensing. As for the trophic webs of the two rodent species, we find that increased vegetation is positively associated with higher temperatures and precipitation for both ecosystems. We furthermore find a positive association between vegetation and ground squirrel density, yet a negative association between vegetation and gerbil density. Our study thus shows how past surveillance records can be used to design and improve existing plague prevention and control measures, by tailoring them to individual plague foci. Such measures are indeed highly needed under present conditions with prevailing climate change.

The Effect of Soil Physical Properties and Soil Microclimate on Rodent Burrows’ Abundance and their Characteristics in Western Usambara Mountains, Tanzania

ABSTRACT The present study was carried out between September 2009 and June 2013 in Western Usambara Mountains plague focus with the aim of establishing the influence of selected soil physical properties and soil microclimate on rodent burrows’ abundance, portal orientation and use. Two landscapes with high and medium plague frequencies in Lokome and Lukozi villages were studied. In the two landscapes data were collected from 117 and 200 observation sites respectively, using 100 m x 200 m quadrats. At each quadrat crossing, a sample quadrat of 20 m x 20 m was demarcated for scanning rodent burrows whereby burrows encountered were counted and their portal orientation and burrow use described. Within each sample quadrat, selected soil physical properties including thickness of the soil genetic horizons and soil dry consistence were determined. Soil samples were collected from each horizon for laboratory texture analysis. Temperature (surface and subsurface to a depth 10 cm) and relative humidity at a depth of 10 and 30 cm were collected using infrared, thermo-couple thermometers and i-Buttons. Descriptive statistics, ANOVA and logistic regression were used to analyse the data by R-software. There were significant (P=.0001) differences between the two landscapes regarding topsoil depth, infrared temperature, relative humidity and rodent burrows’ abundance. In the high plague frequency landscape there was a significant influence (P=.05) of topsoil horizon thickness on rodent burrows’ abundance and use. Results also indicate that soil temperature to a depth of 10 cm was significantly (P=.05) correlated with rodent burrow use. Likewise, in the medium plague frequency landscape, soil physical properties and soil microclimate significantly (P=.0001) discouraged rodent burrowing. It was concluded that soil physical and soil microclimate encouraged and discouraged burrowing in the high and the medium plague frequency landscapes, respectively. The landscape with high rodent burrows’ abundance corresponded with high plague frequency records. Keywords: Rodent burrows; burrows’ abundance; soil microclimate; soil physical properties; plague focus.

Status and Variability of Soil Micronutrients with Landforms in the Plague Focus of Western Usambara Mountains, Tanzania

A study was carried out in Western Usambara, Tanzania to assess the status of soil micronutrients across three geomorphic units viz., plain, escarpment and plateau in order to provide essential information for on-going studies on plague epidemiology. Nineteen soil profiles were opened, described and 54 samples collected for laboratory analysis. Standard methods were employed to

Seasonal fluctuations of small mammal and flea communities in a Ugandan plague focus: evidence to implicate Arvicanthis niloticus and Crocidura spp. as key hosts in Yersinia pestis transmission.

BackgroundThe distribution of human plague risk is strongly associated with rainfall in the tropical plague foci of East Africa, but little is known about how the plague bacterium is maintained during periods between outbreaks or whether environmental drivers trigger these outbreaks. We collected small mammals and fleas over a two year period in the West Nile region of Uganda to examine how the ecological community varies seasonally in a region with areas of both high and low risk of human plague cases.MethodsSeasonal changes in the small mammal and flea communities were examined along an elevation gradient to determine whether small mammal and flea populations exhibit differences in their response to seasonal fluctuations in precipitation, temperature, and crop harvests in areas within (above 1300 m) and outside (below 1300 m) of a model-defined plague focus.ResultsThe abundance of two potential enzootic host species (Arvicanthis niloticus and Crocidura spp.) increased during the plague season within the plague focus, but did not show the same increase at lower elevations outside this focus. In contrast, the abundance of the domestic rat population (Rattus rattus) did not show significant seasonal fluctuations regardless of locality. Arvicanthis niloticus abundance was negatively associated with monthly precipitation at a six month lag and positively associated with current monthly temperatures, and Crocidura spp. abundance was positively associated with precipitation at a three month lag and negatively associated with current monthly temperatures. The abundance of A. niloticus and Crocidura spp. were both positively correlated with the harvest of millet and maize.ConclusionsThe association between the abundance of several small mammal species and rainfall is consistent with previous models of the timing of human plague cases in relation to precipitation in the West Nile region. The seasonal increase in the abundance of key potential host species within the plague focus, but not outside of this area, suggests that changes in small mammal abundance may create favorable conditions for epizootic transmission of Y. pestis which ultimately may increase risk of human cases in this region.

Study of the plasmid profiles and geographical distribution of Yersinia pestis in China

To analyze the plasmid features and geographical distribution characteristics of Yersinia pestis of different plague foci in China. A total of 2 213 Yersinia pestis strains were colected from 11 Chinese plague foci separated during 1943 to 2012, and plasmid DNA according to alkali cracking method, and measured the relative molecular mass (Mr) of plasmid DNA based on the standard plasmid contrast method, then analyzed the plasmid profiles by agar gel electrophoresis. A total of 2 213 strains had 16 kinds of plasmids with different Mr, including 4×10(6), 6×10(6), 7×10(6), 13×10(6), 16×10(6), 20×10(6), 22×10(6), 23×10(6), 27×10(6), 30×10(6), 36×10(6), 45×10(6), 52×10(6), 65×10(6), 72×10(6) and 90×10(6). Plasmid were classified into 26 kinds of plasmid profiles. A total of 2 213 Yersinia pestis strains contained 4 large plasmids, 52×10(6), 65×10(6), 72×10(6) and 90×10(6), whose ratio was 22.10% (589/2 213), 75.60% (1 672/2 213), 0.17% (4/2 213), 2.12% (47/2 213), respectively. Among which, strains with plasmid 52×10(6), 65×10(6), 90×10(6) distributed in Qinghai-Tibet plateau Himalayan Marmot natural plague foci, strains with 72×10(6) plasmid only distributed in Inner Mongolia Meriones unguiculatus natural plague foci and Junggar Basin R. opimus natural plague foci, and 65×10(6) plasmid distributed in all the other foci. Strains in Chinese 11 plague foci contained 4 kinds of large plasmid, the Mr respectively were 52×10(6), 65×10(6), 72×10(6), 90×10(6), which were classified into 26 kinds of plasmid profiles with other plasmid. These plasmid profiles distributed in relatively independent epidemic focus.

We are connected: flea–host association networks in the plague outbreak focus in the Rift Valley, northern Tanzania

Context Plague is a serious health problem in northern Tanzania, with outbreaks since 2008 in two districts located in Rift Valley. There is dearth of knowledge on diversity of small mammal and flea fauna occurring in this plague focus. Knowledge on interactions between fleas and rodent species that harbour the plague bacterium, Yersinia pestis, is important for developing strategies for control and prevention of plague. Aims This study aims to show how rodents and fleas are associated with each other in the plague focus. Methods Animals were trapped bimonthly from 2009 to 2012 in different habitats. The fur of animals was brushed to collect fleas, which were identified and quantified. Network analysis methods, randomisation and rarefaction curves were used to show how hosts and fleas are associated. Key results Thirteen species of rodents were associated with 26 species of fleas of which Dinopsyllus lypusus, Xenopsylla brasiliensis and X. cheopis are confirmed efficient vectors of Y. pestis. Randomisation and rarefaction curves established that Lophuromys flavopunctatus had significantly higher flea species richness (n = 9) than did all other hosts, whereas Xenopsylla cheopis and Dinopsyllus spp. showed greater host species richness than did other species of fleas. There was no significant correlation between host sex and flea abundance (χ2 = 0.8, d.f. = 6, P = 0.371), but significant differences between reproductive states (adults had more fleas than did subadults) were observed, which probably reflected typical positive correlation between size and flea abundance (χ2 = 4.1955, d.f. = 1, P = 0.040). Conclusions The plague outbreak focus in northern Tanzania has a diverse fauna of rodents and fleas with multiple patterns of association and connectivity. Implications Existence of diverse populations of rodents associated with a large number of flea species, some of which are efficient plague vectors, increases the potential for persistence and transmission of plague to humans in northern Tanzania.

A study on the taxonomy of soil amoebas from Caspian plague foci based on an analysis of ribosomal operon sequences

The results of a study on the taxonomy and quantitative abundance of free-living amoebas in soil samples from the Russian plague foci of the northwestern Caspian steppe, the Caspian sand, and the Volga-Ural steppe are presented. Amoebas of the Willaertia and Hartmanella genera, as well as representatives of myxomycetes, were isolated from samples. From these, amoebas of the Acanthamoeba genus predominated and could be as abundantas 300000 cells per 1 g of soil. Sequencing of the 18S rRNA gene region showed that Acanthamoeba from the Volga-Ural steppe focus belonged to the A. castellanii species. Phylogenetic analysis confirmed that amoebas from two other Caspian foci belonged to the species of Acanthamoeba spp.

Preliminary prospects of assessment using telemetry in the study of gerbils’ mobility in natural plague focus

The article shows that a relatively quick obtaining direct and most importantly absolutely accurate data on individual movements of marked individuals, based on field research in 2012-2014 makes telemetry a very promising direction in mobility study of the potential plague hosts in natural focus of this infection. It is concluded that methods of telemetry are likely applicable not only for rodents but also for any other small mammals, for which catch methods on alive animals are practiced.

Оценка эпизоотологической значимости блох (Insecta, Siphonaptera) в феномене сезонности проявления чумы в степных природных очагах чумы сусликового типа Северного, Северо-Западного Прикаспия и Предкавказья

Оценка эпизоотологической значимости блох (Insecta, Siphonaptera) в феномене сезонности проявления чумы в степных природных очагах чумы сусликового типа Северного, Северо-Западного Прикаспия и Предкавказья

Intraspecies classification of rhamnose-positive Yersinia pestis strains from natural plague foci of Mongolia

Comparative analysis of rhamnose-positive Y. pestis strains, which are traditionally recognized as the biovar altaica, was performed with the use of molecular typing. The strains were isolated from the natural plague foci of the Changay mountainous system and the Sailugem natural plague focus in Mongolia. The Russian part of the latter is known as the Altai Mountains focus (focus 36). All isolates were compared with the other rhamnose-positive vole strains from the natural plague foci located in the grassland of Xilingol (focus L, China), the plateau of Qinghai-Tibet (focus M, China), the Gissarian Ridge (focus 34, Tadjikistan and Uzbekistan), and the Talassian Ridge (focus 40, Kyrgyzstan). The strains studied formed a single cluster with two branches, of which the first branch included the talassica (0.PE4?), qinghaiensis (0.PE4ab), and xilingolensis (0.PE4cd) phylogenetic groups, while the second included the hissarica (0.PE9) and altaica (0.PE1) phylogenetic groups. The results of molecular typing suggest that several strains from the Qinghai group of the Mongolian foci belong to the qinghaiensis and xilingolensis biovars but not to the altaica biovar.

Anthropourgic Foci of Plague in Vietnam: Past and Present

The review contains the results of ecological-epizootiological and epidemiological investigations of plague in the territory of the Socialist Republic of Vietnam in 1989-2012. Studied has been the structure of epizootic triad - carrier-vector-pathogen. There is a low probability of plague foci occurrence in zones of tropical forests and savanna under the conditions of humid subequatorial climate. Main plague agent carrier on the Thai Nguyen Plateau is the synanthropic little rat, Rattus exulans . Specialized fleas species are absent on wild-living rats Rattus genus, as well as mice, and bandicoots, and the abundance of other species is small. It has been demonstrated that all the elements of the parasitic plague system are classified as introduced species. Thereupon it is inferred that plague foci in Vietnam are anthropourgic and are of anthropogenic origin solely. Plague cases in humans across the territory of the country were registered between 1898 and 2002. The most persistent ones functioned on the Thai Nguyen Plateau. Although epizootic activity of the foci in territory of the former endemic provinces has decreased, it is necessary to continue epizootiological monitoring further on in the modern period.

Infection of an Individual with Plague in the Gorno-Altaisk High-Mountain Natural Focus in 2014. Communication 1. Epidemiological and Epizootiological Peculiarities of Plague Manifestations in the Gorno-Altaisk High-Mountain (Sailyugemsky) Natural Plague Focus

For the first time ever since the discovery of the Gorno-Altaisk high-mountain natural focus in 1961, registered has been a case of human plague infection. It occurred in the consequence of the grey marmot cutting that was caught in the territory of one of the persistent epizootic regions of the natural plague focus. The outbreak was localized and eliminated following complex anti-epidemic measures, including medical treatment of the patient; identification, isolation and management of the contact persons, both to the patient and marmot; withdrawal and disposal of marmots’ carcasses, obtained during unauthorized commercial hunting; specific and non-specific prophylaxis of the disease. Also for the first time ever received have been the evidences of concurrent circulation of the strains, subspecies Y. pestis ssp pestis and Y. pestis ssp. altaica in the regions of cohabitation of Pallas’ pika (Ochotona pallasi), Siberian souslik (Citellus undulatus), and grey marmot. Specified is the necessity to reconsider the tactics of epizootiological plague monitoring in enzootic territories where circulation of various Y. pestis subspecies is registered.

Designing of the Software Program “Epidemic Potential of Natural Plague Foci in the Territory of the Russian Federation”

Designed has been a computer program “Epidemic potential of natural plague foci in the Russian Federation” applied for the automatized evaluation of the epidemic hazard level of natural plague foci in relation to the population residing on the territory of them. This software optimizes management decision making via provision of the Heads of the Rospotrebnadzor organizations with the comprehensive current data on the sanitary-epidemiological situation on plague across the whole territory of the natural foci in Russia, and by enhancing the quality of the visual data display, which are essential for the decision making in the sphere of biological safety provision. In consequence of integration into “Deductor” software program, counted value of epidemic potential for any location of the natural focus territory can be ranked correspondently using colorimetric scale (from red up violet color, for maximum and minimum rating, respectively). The program is designed on the base of Arc GIS Platform to be introduced into the automatized information analysis system for the provision of biological safety in the constituent entities of the Russian Federation.

Enzootic plague foci, Algeria.

In Algeria, PCR sequencing of pla, glpD and rpoB genes found Yersinia pestis in 18/237 (8%) rodents of five species, including Apodemus sylvaticus, previously undescribed as pestiferous; and disclosed three new plague foci. Multiple spacer typing confirmed a new Orientalis variant. Rodent survey should be reinforced in this country hosting reemerging plague.

Dynamics of CRISPR loci in microevolutionary process of Yersinia pestis strains.

The potential use of CRISPR loci genotyping to elucidate population dynamics and microevolution of 146 Yersinia pestis strains from different biovars and locations was investigated in this work. The majority of strains from the Orientalis biovar presented specific spacer arrays, allowing for the establishment of a CRISPR signature for their respective isolates. Twenty-one new spacers were found in the Y. pestis strains from plague foci in Brazil. Ninety-three (64%) strains were grouped in the G1 genotype, whereas the others were distributed in 35 genotypes. This study allowed observing a microevolutionary process in a group of Y. pestis isolated from Brazil. We also identified specific genotypes of Y. pestis that were important for the establishment of the bacteria in plague foci in Brazil. The data have provided supporting evidence for the diversity and dynamics of CRISPR loci present in the genome of Y. pestis strains from plague foci in Brazil.

Concerning the Allocation of Emerging Natural Foci of the Currently Important Infectious Diseases in the West of Kazakhstan

Within the period of 2000-2011, in the West of Kazakhstan, identified have been five, previously unknown in the territory, natural foci of dangerous infectious diseases such as hemorrhagic fever with renal syndrome, Astrakhan spotty fever, Crimean hemorrhagic fever, West Nile fever, and tick-borne viral encephalitis. The reason is that key ecological factors for the persistence of the infections in the local biocoenoses occurred. It is characteristic that circulation of the agents of new infectious diseases is registered in the territory of the long-established natural plague and tularemia foci. Since 2000 and on, hemorrhagic fever with renal syndrome morbidity is registered in the Western-Kazakhstan Region on a regular basis. There is some evidence to identification of West Nile fever patients in the territory of Russia in 2012, which came from Kazakhstan. Based on the spatial distribution of the natural foci of various infections, Western-Kazakhstan Region has been subdivided into four areas. In order to provide for the effective prophylaxis of emerging diseases, it is essential that healthcare facilities and services dealing with infectious diseases are consolidated and reinforced, and epidemiological surveillance is improved with the current conditions in mind.

List of World Fauna Vertebrate Animals - Carriers of Plague Agent

Consequently to the long-term investigations conducted in natural and anthropourgic foci of plague, situated in Africa, Eurasia, North and South America, identified were not less than 340 species of mammals and birds infected with plague agent. The paper contains the list of plague agent carriers described, both in domestic and foreign publications.

Application of Dot-Immunoassay for Detection of Plague Agent Antigens in the Field Samples

CFU/ml) and soluble antigens (FI) − ≥ 4.8 ng/ml and high specificity, confirmed by the absence of false-positive reactions with five heterologous microorganisms. The test-systems were used for Y. pestis antigen detection in field material from the territory of the Altai mountain natural plague focus by dot-immunoassay with comparison of the received results in passive hemagglutination reaction. Test-systems possessed a number of advantages as compared to routine serological reactions and could be applied with success by practical public health services both in stationary and field conditions.