Genetic diversity of Rhombomys opimus and Meriones meridianus with potential divergence of plague resistance in the Junggar Basin plague focus based on RT1-Db1*exon1.

In the Junggar Basin plague focus, Rhombomys opimus and Meriones meridianus live together, and their parasitic fleas have a similar community structure. However, R. opimus has significantly higher positive rates of Yersinia pestis and anti-F1 antibody compared with M. meridianus. In this study, Y. pestis- and antiF1 antibody-negative R. opimus and M. penicilliger were collected in Qitai county, Fukang city and Mulei county of the eastern part of the Junggar Basin. The genomic DNA was extracted from their spleen tissues, and RT1-Db1*exon1 was amplified through PCR procedure and then sequenced. Sequence analysis was performed and molecular diversity parameters were calculated and compared. The results showed that there were significant differences in nucleotide composition, amino acid composition, number and distribution of single nucleotide polymorphism (SNP) sites and number of haplotypes between R. opimus and M. penicilliger. The nucleotide diversity (π) for R. opimus was 0.00420 ± 0.00139, the haplotype diversity (h) was 0.833 ± 0.086, and the average number of nucleotide differences (K) was 2.02564. The π for M. penicilliger was 0.06569 ± 0.02524, and the h was 1.000 ± 0.045, and the K was 10.4444. The fixation index (FST) value between R. opimus and M. penicilliger was 0.9207. Furthermore, the FST value within R. opimus (0.0275) was significantly lower than that within M. penicilliger (0.2106), indicating a greater genetic variation of M. penicilliger compared with R. opimus. In conclusion, the genetic diversity analysis based on RT1-Db1*exon1 showed that M. penicilliger had higher gene polymorphism and greater genetic differentiation compared with R. opimus in the Junggar Basin plague focus, which might be associated with the low infection rate of Y. pestis.

Flea index predicts plague epizootics among great gerbils (Rhombomys opimus) in the Junggar Basin China plague focus.

BACKGROUND: The Junggar Basin plague focus was the most recently identified natural plague focus in China. Through extensive field investigations, great gerbils (Rhombomys opimus) have been confirmed as the main host in this focus, and the community structure of their parasitic fleas is associated with the intensity of plague epizootics. The aim of this study is to provide an indicator that can be surveyed to evaluate the risk of plague epizootics. METHODS: Between 2005 and 2016, rodents and fleas were collected in the Junggar Basin plague focus. The parasitic fleas on great gerbils were harvested, and anti-F1 antibody in the serum or heart infusion of great gerbils was detected through indirect hemagglutination assay. Yersinia pestis (Y. pestis) was isolated from the liver and spleen of great gerbils and their parasitic fleas using Luria-Bertani plates. Receiver-operating characteristic (ROC) curve was used to evaluate the predictive value of flea index. RESULTS: Between 2005 and 2016, 98 investigations were performed, and 6778 great gerbils and 68,498 fleas were collected. Twenty-seven rodents were positive for Y. pestis isolation with a positivity rate of 0.4%; 674 rodents were positive for anti-F1 antibody with a positivity rate of 9.9%. Among these 98 investigations, plague epizootics were confirmed in 13 instances by Y. pestis-positive rodents and in 59 instances by anti-F1 antibody-positive rodents. We observed a higher flea index among rodents with confirmed plague epizootic compared to the negative ones (P = 0.001, 0.002), with an AUC value of 0.659 (95% CI: 0.524-0.835, P = 0.038) for Y. pestis-positive rodents and an AUC value of 0.718 (95% CI: 0.687-0.784, P < 0.001) for anti-F1 antibody-positive rodents. CONCLUSIONS: Significantly higher flea index was associated with confirmed plague epizootic cases among great gerbils and could be used to predict plague epizootics in this focus.

Molecular identification of common hard ticks (Acari: Ixodidae) in Xinjiang, China.

We provide data on the cytochrome c oxidase subunit I (COI) and 16S rDNA genes for eight species of common hard ticks in Xinjiang: Dermacentor montanus, D. niveus, Haemaphysalis sulcate, Hyalomma asiaticum asiaticum, Hya. detritum, Hya. scupense, Rhipicephalus sanguineus and R. pumilio. Genetic distances, calculated based on the Kimura two-parameter (K2P) distance model, found the same trend of intraspecies level≤interspecies levelintragenus level. Phylogenetic trees, constructed with the neighbor-joining (NJ) and minimum-evolution (ME) methods, demonstrated that each species clustered into separate clades, thus confirming the usefulness of CO1 and 16S rDNA genes for tick species identification. The genera Dermacentor, Haemaphysalis and Rhipicephalus were all recovered in the phylogenetic analysis, as was the subfamily Rhipicephalinae, but a monophyletic Hyalomma was not.

A new strain of Crimean-Congo hemorrhagic fever virus isolated from Xinjiang, China.

Crimean-Congo hemorrhagic fever virus (CCHFV) is a highly pathogenic tick-borne virus with a fatality rate of up to 50% in humans. CCHFV is widely distributed in countries around the world. Outbreaks of CCHFV infection in humans have occurred in prior years in Xinjiang Province, China. Epidemiological surveys have detected CCHFV RNA in ticks and animals; however, few isolates were identified. In this study, we identified and isolated a new CCHFV strain from Hyalomma asiaticum asiaticum ticks collected from north of Tarim Basin in Xinjiang, China. A preliminary investigation of infection and antigens expression of CCHFV was performed in newborn mice. The target tissues for CCHFV replication in newborn mice were identified. The analysis of the phylogenetic relationships with other Chinese strains suggested that diverse genotypes of CCHFV have circulated in Xinjiang for years. These findings provide important insights into our understanding of CCHFV infection and evolution as well as disease prevention and control for local residents.

Transmission efficiency of the plague pathogen (Y. pestis) by the flea, Xenopsylla skrjabini, to mice and great gerbils.

BACKGROUND: Plague, a zoonotic disease caused by Yersinia pestis, is characterized by its ability to persist in the plague natural foci. Junggar Basin plague focus was recently identified in China, with Rhombomys opimus (great gerbils) and Xenopsylla skrjabini as the main reservoir and vector for plague. No transmission efficiency data of X. skrjabini for Y. pestis is available till now. METHODS: In this study, we estimated the median infectious dose (ID50) and the blockage rates of X. skrjabini with Y. pestis, by using artificial feeders. We then evaluated the flea transmission ability of Y. pestis to the mice and great gerbils via artificial bloodmeal feeding. Finally, we investigated the transmission of Y. pestis to mice with fleas fed by infected great gerbils. RESULTS: ID50 of Y. pestis to X. skrjabini was estimated as 2.04 × 10(5) CFU (95% CI, 1.45 × 10(5) - 3.18 × 10(5) CFU), around 40 times higher than that of X. cheopis. Although fleas fed by higher bacteremia bloodmeal had higher infection rates for Y. pestis, they lived significantly shorter than their counterparts. X. skrjabini could get fully blocked as early as day 3 post of infection (7.1%, 3/42 fleas), and the overall blockage rate of X. cheopis was estimated as 14.9% (82/550 fleas) during the 14 days of investigation. For the fleas infected by artificial feeders, they seemed to transmit plague more efficiently to great gerbils than mice. Our single flea transmission experiments also revealed that, the transmission capacity of naturally infected fleas (fed by infected great gerbils) was significantly higher than that of artificially infected ones (fed by artificial feeders). CONCLUSION: Our results indicated that ID50 of Y. pestis to X. skrjabini was higher than other fleas like X. cheopis, and its transmission efficiency to mice might be lower than other flea vectors in the artificial feeding modes. We also found different transmission potentials in the artificially infected fleas and the naturally infected ones. Further studies are needed to figure out the role of X. skrjabini in the plague epidemiological cycles in Junggar Basin plague focus.

[Study on the spatial distribution and related risks of Rhombomys opimus, based on the ecological niche modeling in Junggar Basin, Xinjiang].

OBJECTIVE: In order to understand the distribution of the host animals in Junggar Basin, this study intended to map the spatial distribution and identifying the risk of Rhombomys opimus in the framework of ecological niche theory based on the "3S" technology. METHODS: Data on Rhombomys opimus was obtained through a series of field surveys. Environmental variables were achieved through data from Remote Sensing. Maxent modeling was built to map the potential distribution of Rhombomys opimus, with its risks identified. RESULTS: The prediction model showed ideal accuracy, with the AUC value as 0.968. Probability of Maximum Youden Index was defined as the threshold being used. The sensitivity and specificity showed as 91.4% and 63.3%, respectively. The accuracy was 73.8%, and the Kappa coefficient was 0.495. The positive predictive value was 59.7%. The negative predictive value was 92.6%. The predicted high risk area was 37 304 km2, with 6.2% in the whole area, distributed in 18 counties, including Changji Hui Autonomous Prefecture, Urumqi, Karamay and so on. The number of people under high risk would come about 120 000, scattering in the areas of 261 square kilometers. CONCLUSION: It was feasible to predict the potential distribution of Rhombomys opimus based on the ecological niche theory as well as environmental variables derived from data through remote sensing. More specific high-risk areas could be identified under this technique so as to guide the monitoring programs.

[Study on the spatial and temporal distribution of animal plague in Junggar Basin plague focus].

OBJECTIVE: To explore the spatial and temporal distributions of animal plague in Junggar Basin natural plague focus. METHODS: Data regarding plague antibody (F1) in serum of Great Gerbil (Rhombomys opimus, R. opimus) which were collected from 2005 to 2012 in Junggar Basin and analyzed. The changing rates on the positivity of F1 that appeared spatially and temporally were also analyzed. RESULTS: A total of 4 825 R. opimus serum samples were collected in 13 administrative regions in Junggar Basin. RESULTS: showed that plague R. opimus existed in two areas-Gurbantonggut desert in the eastern-center and the clay desert of western Junggar Basin. However, in these two areas, the intensity of animal plague prevalence was different. In the former region where Yesinia pestis positive serum was detected from R. opimus, the detected rate of R. opimus was 8.39%. However, in the latter areas, the average positive rate was 1.56%. The changing trends of R. opimus plague prevalence were also varied annually. In the western Junggar Basin, the trend showed a slowly downward profile. The serum positive rate of R. opimus for Yesinia pestis decreased, from 7.59% in 2005 to 0.61% in 2008, and appeared as a resting state that none of the positive sample could be found since then. However, in the eastern-center Junggar Basin area-also named as Gurbantonggut desert which had been divided into 3 segments(western, central and eastern, according to related geographical characteristics), the changing trends of animal plague seemed quite complex. In the western segment, the animal plague had two epidemic peaks-in 2006 and 2010, with the interval of 4 years, with the higher peak of all the three geographic segments as 45.65% in 2010 and the positive serum of R. opimus for plague could be detected each year from 2006 to 2012. However, there were 3 epidemic peaks in the same period in the central and eastern segments. In the central segment, the peaks appeared in 2006, 2009 and 2011, with the intervals as 2.5 years and the average positive rate 8.92% was seen the lowest in Gurbantonggut desert. In the eastern segment, the first 2 peaks appeared the same season as in the central segment, but the third peak appeared in 2012, with the peak interval as 3 years. The positive rate of R. opimus for plague was also different in seasons, with the positive rate higher in autumn than in spring. These findings showed that the animal plague could be continuously prevalent from spring to autumn in the natural foci of plague in the Junggar Basin. CONCLUSION: Both geographical and temporal fluctuations of animal plague existed in the natural foci of Junggar Basin which was also named as geographical heterogeneity. Consequently, animal plague could be divided into two areas-the clay plains desert in the western and the Gurbantonggut desert in the eastern-center Junggar Basin.

[Community structure of Great Gerbils (Rhombomys opimus) parasitic fleas in Junggar Basin focus and related epizootiological characteristics on plague].

OBJECTIVE: To understand the community structure of Rhombomys opimus parasitic fleas in the natural plague focus in Junggar Basin, so as to explain the relationship between the community structure and the prevalence of animal plague in this area. METHODS: The body fleas of R.opimus which were collected in 2005-2010 from the Junggar Basin was analysed by community ecology method, an each clustered flea community was compared with information of pathogenic and serological indicators of animal plague epidemic by statistic method. RESULTS: The community structure of R. opimus parasitic fleas included 19 species and was very complicated, with only 3 were identified as 'common' species but the others belonged to 'rare' species. Both the average richness and diversity of flea community were higher, as 1.66 and 1.5556, with dominance not obvious (0.332) and the homogeneity as moderate (0.5283). The community structure of R. opimus parasitic fleas could be changed by the following factors as: the rates of flea parasitic/flea index and the proportions of main fleas etc. The flea community could be divided into 5 clusters according to the above said elements. All these data showed that the fleas of R. opimus parasitic fleas possess the nature of multi-parasitism. CONCLUSIONS: The community of R. opimus parasitic fleas existed heterogeneous of geographic region, and this phenomenon associated with the animal plague epidemic strength.

Dynamics of Yersinia pestis and its antibody response in great gerbils (Rhombomys opimus) by subcutaneous infection.

BACKGROUND: Rhombomys opimus (great gerbil) is a reservoir of Yersinia pestis in the natural plague foci of Central Asia. Great gerbils are highly resistant to Y. pestis infection. The coevolution of great gerbils and Y. pestis is believed to play an important role in the plague epidemics in Central Asia plague foci. However, the dynamics of Y. pestis infection and the corresponding antibody response in great gerbils have not been evaluated. In this report, animal experiments were employed to investigate the bacterial load in both the liver and spleen of infected great gerbils. The dynamics of the antibody response to the F1 capsule antigen of Y. pestis was also determined. METHODOLOGY: Captured great gerbils that tested negative for both anti-F1 antibodies and bacterial isolation were infected subcutaneously with different doses (10(5) to 10(11) CFU) of a Y. pestis strain isolated from a live great gerbil during routine plague surveillance in the Junggar Basin, Xinjiang, China. The clinical manifestations, changes in body weight, anal temperature, and gross anatomy of the infected animals were observed. The blood cell count, bacterial load, and anti-F1 antibody titers were determined at different time points after infection using a blood analyzer, plate counts, and an indirect hemagglutination assay, respectively. CONCLUSIONS/SIGNIFICANCE: The dynamics of bacterial load and the anti-F1 antibody concentration in great gerbils are highly variable among individuals. The Y. pestis infection in great gerbils could persist as long as 15 days. They act as an appropriate reservoir for plague in the Junggar Basin, which is part of the natural plague foci in Central Asia. The dynamics of the Y. pestis susceptibility of great gerbil will improve the understanding of its variable resistance, which would facilitate the development of more effective countermeasures for controlling plague epidemics in this focus.

[Study on the situation of plague in Junggar Basin of China].

OBJECTIVE: To understand the distribution, fauna, population structure of host animals and their parasitic fleas as well as popular dynamic of animal plague of natural plague foci in Junggar Basin. METHODS: Sample materials and data of animals and vector insects were collected using ecological methods and the population structures were analyzed statistically. F1 antibody of Yersinia pestis in rodents' serum and organ suspension was detected by means of IHA while the pathogen of Y. pestis in rodents and vector insects was detected by means of aetiological detections and the isolated Y. pestis was detected using biochemical methods. RESULTS: The small mammals which were found in Junggar Basin belonged to 17 species of 11 genera 7 families. Of them, 13 species of rodents were included whose parasitic fleas belonged to 19 species of 10 genera 8 families. The average coverage of Rhombomys opimus hole-community was 22.5% in Junggar Basin with the average density of R. opimus hole-community was 15.9/hm2 and the average rate of habitat of the hole-community was 70.2%. In the R. opimus community, the average density of rodents was 3.1/hole-community, and 34.4/hm2 in the nature plague foci. In the population structure of the hole-community of R. opimus, R. opimus accounted for 72.9% in the total captured rodents, Meriones meridianus was 24.5% while the others were 2.6%. In the nocturnal community of rodents, M. meridianus accounted for 64.0% in total captured rodents, Dipus sagitta was 15.1%, M. erythrourns was 7.5% and the others were 13.4%. In the rodents community of Junggar Basin, the rate of R. opimus with fleas was 84.9%, which was the highest, followed by M. tamariscinus, Euchoreutes naso and M. erythrourns, with the rates as 71.4%, 66.7% and 62.7% respectively. The rate of M. meridianus with fleas was 38.3%. There were 16 species of parasitic fleas in R. opimus, with the total flea index as 8.58 and the dominant species was Xenopsylla skrjabini. There were 17 and 16 kinds of fleas in M. erythrourns and M. meridianus respectively with the total flea index were 1.59 and 1.15, with dominant fleas were Nosopsyllus laeviceps and X. skrjabini. The serum and organ suspension of 3179 rodents which belonged to 12 species were detected by means of IHA, of them 174 samples were positive and the positive rate was 5.5%. There were 1356 samples of R. opimus in these materials, and 164 were positive, accounted for 12.1%. The samples of M. meridianus were 1255, with 9 positive, accounted for 0.7%. The samples of D. sagitta were 116 with 1 positive and the rate was 0.9%. The samples of other rodents were 452 but were all negative. There were in total 2975 organs collected from rodents, when detected by methods of isolated of Y. pestis. 15 strains of Y. pestis were isolated from 1243 R. opimus, and 2 strains isolated from 1230 M. meridianus. A total number of 11 647 fleas from rodents were detected by methods of isolated of Y. pestis in which 1 strain of Y. pestis was isolated from 4713 X. skrjabini, and 6 were isolated from 2101 Xenopsylla minax, 1 from 328 Xenopsylla conformis conformis and 1 from 250 Echidnophaga oschanini. Among the other 4255 fleas, none was isolated. The biochemical properties of these Y. pestis which isolated from Junggar Basin were positive of Maltose, Ejiao sugar and Glycerol, and negative of Rhamnose and Nitrogen, which were all strongly poisonous to mouse. CONCLUSION: The natural plague foci in Junggar Basin spread all over the whole Junggar Basin. There were animal plague cases found in 12 counties (cites) while Karamy, Bole, Jimusaer and Qitai were confirmed as plague foci counties (cities). Animals and vector insects of the foci were complicated but the ecological system was stable. R. opimus was recognized as the dominant host animal and its biochemical type belonged to the Middle Ages, suggesting that the foci was a new type of natural plague foci.