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Streptomycin is considered to be one of the effective antibiotics for the treatment of plague. In order to investigate the streptomycin resistance of Y. pestis in China, we evaluated streptomycin susceptibility of 536 Y. pestis strains in China in vitro using the minimal inhibitory concentration (MIC) and screened streptomycin resistance-associated genes (strA and strB) by PCR method. A clinical Y. pestis isolate (S19960127) exhibited high-level resistance to streptomycin (the MIC was 4,096 mg/L). The strain (biovar antiqua) was isolated from a pneumonic plague outbreak in 1996 in Tibet Autonomous Region, China, belonging to the Marmota himalayana Qinghai–Tibet Plateau plague focus. In contrast to previously reported streptomycin resistance mediated by conjugative plasmids, the genome sequencing and allelic replacement experiments demonstrated that an rpsL gene (ribosomal protein S12) mutation with substitution of amino-acid 43 (K43R) was responsible for the high-level resistance to streptomycin in strain S19960127, which is consistent with the mutation reported in some streptomycin-resistant Mycobacterium tuberculosis strains. Streptomycin is used as the first-line treatment against plague in many countries. The emergence of streptomycin resistance in Y. pestis represents a critical public health problem. So streptomycin susceptibility monitoring of Y. pestis isolates should not only include plasmid-mediated resistance but also include the ribosomal protein S12 gene (rpsL) mutation, especially when treatment failure is suspected due to antibiotic resistance., Author summary The plague natural foci are widely distributed in the world, and correspondingly, the plague still poses a significant threat to human health in some countries with endemic plague foci. Streptomycin is used as the first-line treatment against plague in many countries for the antibiotic is considered to be one of the effective antibiotics, particularly for the treatment of pneumonic plague. The resistance to streptomycin had been reported in Y. pestis strains from Madagascar in previous studies. In this study, we reported the high-level resistance to streptomycin in a clinical isolate of Y. pestis from a pneumonic patient in Tibet Autonomous Region, China, and a novel mechanism of streptomycin resistance, i.e. mutation in the rpsL gene were identified. The knowledge acquired about streptomycin resistance in Y. pestis will remain of great practical value. For the emergence of resistance to streptomycin in Y. pestis would render the treatment failure, thus corresponding antibiotic monitoring should be routinely carried out in countries threatened by plague. In addition, based on our further understanding about streptomycin resistance of Y. pestis isolates, such monitoring should not only include plasmid-mediated resistance but also include the ribosomal protein S12 gene (rpsL) mutation in Y. pestis isolates.

Plague, which is caused by Yersinia pestis (Y. pestis), is a typical enzootic disease that is cycled among rodent reservoirs by flea vectors. Nineteen distinct plague foci have been characterized in China. Y. pestis strains from these foci exhibit considerable genetic variation because of gene acquisition, loss, and inactivation, which promote its microevolution and the expansion of various endemic plague foci. Available evidence suggests that Y. pestis microevolution likely results from complex interactions among the environment, hosts, vectors, and Y. pestis.

Yersinia pestis is the etiological agent of the notorious plague that has claimed millions of deaths in history. Of the four known Y. pestis biovars (Antiqua, Medievalis, Orientalis, and Microtus), Microtus strains are unique for being highly virulent in mice but avirulent in humans. Here, human peripheral lymphocytes were infected with the fully virulent 141 strain or the Microtus strain 201, and their transcriptomes were determined and compared. The most notable finding was that robust responses in the pathways for cytokine-cytokine receptor interaction, chemokine signaling pathway, Toll-like receptor signaling and Jak-STAT signaling were induced at 2 h post infection (hpi) in the 201- but not the 141-infected lymphocytes, suggesting that human lymphocytes might be able to constrain infections caused by strain 201 but not 141. Consistent with the transcriptome results, much higher IFN-γ and IL-1β were present in the supernatants from the 201-infected lymphocytes, while inflammatory inhibitory IL-10 levels were higher in the 141-infected lymphocytes. The expressions of CSTD and SLC11A1, both of which are functional components of the lysosome, increased in the 201-infected human macrophage-like U937 cells. Further assessment of the survival rate of the 201 bacilli in the U937 cells and murine macrophage RAW 264.7 cells revealed no viable bacteria in the U937 cells at 32 hpi.; however, about 5–10% of the bacteria were still alive in the RAW264.7 cells. Our results indicate that human macrophages can clear the intracellular Y. pestis 201 bacilli more efficiently than murine macrophages, probably by interfering with critical host immune responses, and this could partially account for the host-specific pathogenicity of Y. pestis Microtus strains.

The plague, which is caused by the Gram-negative coccobacillus bacterium Yersinia pestis, has been classified as a reemerging infectious disease by the World Health Organization. The Qinghai-Tibet Plateau natural plague focus is the largest plague focus in China, and Marmota himalayana is the primary host of the plague. Tibetan sheep (Ovis aries) were first identified as naturally infected hosts of Y. pestis based on etiological evidence in 1975, and activities such as slaughtering or skinning Tibetan sheep that have been infected by Y. pestis or died from Y. pestis infection had caused severe human plague in Qinghai. Tibetan sheep are important domestic livestock in the Qinghai-Tibet Plateau. Knowledge regarding the infection rate of Y. pestis in Tibetan sheep is important for understanding the range of infection and improving measures to control plague epidemics in this area. In this study, a serological survey involving 12,710 Tibetan sheep in all 44 counties in Qinghai Province was conducted. The total positive rate of indirect hemagglutination assay for Y. pestis in Tibetan sheep in Qinghai was 0.68% (86/12,710). Serological positivity to the Y. pestis F1 antibody was found in Tibetan sheep in all prefectures, except the Haidong and Haibei prefectures in Qinghai, with the seropositive rate in different counties ranging from 0.33% to 5.2% and the titers in the positive sera ranging from 1:20 to 1:5120. In addition, the seropositive rates in animal plague focus counties were higher than the rates in non-animal plague counties. Such results indicated a widespread infection of Tibetan sheep with Y. pestis in Qinghai, even though only sporadic epidemics of Tibetan sheep plague have been reported in Qinghai.

Background Plague, caused by the bacterium Yersinia pestis, is a highly infectious, zoonotic disease. Hundreds of human plague cases are reported across the world annually. Qinghai Plateau is one of the most severely affected plague regions in China, with more than 240 fatal cases of Y. pestis in the last 60 years. Conventional epidemiologic analysis has effectively guided the prevention and control of local plague transmission; however, molecular genetic analysis is more effective for investigating population diversity and transmission. In this report, we employed different genetic markers to analyze the population structure of Y. pestis in Qinghai Plateau. Methodology/Principal finding We employed a two-step hierarchical strategy to analyze the phylogeny of 102 Qinghai Plateau isolates of Y. pestis, collected between 1954 and 2011. First, we defined the genealogy of Y. pestis by constructed minimum spanning tree based on 25 key SNPs. Seven groups were identified, with group 1.IN2 being identified as the dominant population. Second, two methods, MLVA and CRISPR, were applied to examine the phylogenetic detail of group 1.IN2, which was further divided into three subgroups. Subgroups of 1.IN2 revealed a clear geographic cluster, possibly associated with interaction between bacteriophage and Y. pestis. More recently, Y. pestis populations appear to have shifted from the east toward the center and west of Qinghai Plateau. This shift could be related to destruction of the local niche of the original plague focus through human activities. Additionally, we found that the abundance and relative proportion of 1.IN2 subgroups varied by decade and might be responsible for the fluctuations of plague epidemics in Qinghai Plateau. Conclusion/Significance Molecular genotyping methods provided us with detailed information on population diversity and the spatial-temporal distribution of dominant populations of Y. pestis, which will facilitate future surveillance, prevention, and control of plague in Qinghai Plateau., Author summary Plague is a highly infectious disease caused by the Yersinia pestis bacterium. Since the first strain of Y. pestis was isolated in Qinghai in 1954, confirmed plague cases have occurred nearly every year, and more than 240 people have died from plague over the past 60 years. In this study, we analyzed 102 Y. pestis strains collected from Qinghai Plateau between 1954 and 2011. We determined their genetic diversity and inferred their spatial-temporal distribution, based on genetic markers including SNPs, VNTRs and CRISPRs. Our results indicate that 1.IN2 is the dominant group of Y. pestis in Qinghai Plateau, and its three subpopulations revealed clear geographic clustering that might be driven by interaction with bacteriophages. We observed that the Y. pestis population has moved from the east of Qinghai Plateau to central and western regions over the past 60 years. We also found that the abundance and relative proportion of 1.IN2 subgroups varied over time, leading to fluctuations in plague epidemics. These results extend our knowledge of the genetic diversity of Y. pestis, and its population dynamics in natural plague foci over a number of years. With ongoing risk of outbreaks, we recommend enhanced surveillance in this region.

To develop a safe and effective live plague vaccine, the ΔyscB mutant was constructed based on Yersinia pestis biovar Microtus strain 201 that is avirulent to humans, but virulent to mice. The virulence, immunogenicity and protective efficacy of the ΔyscB mutant were evaluated in this study. The results showed that the ΔyscB mutant was severely attenuated, elicited a higher F1-specific antibody titer and provided protective efficacy against bubonic and pneumonic plague in mouse model. The ΔyscB mutant could induce the secretion of both Th1-associated cytokines (IFN-γ, IL-2 and TNF-α) and Th2-associated cytokines (IL-4 and IL-10). Taken together, the ΔyscB mutant represented a potential vaccine candidate based on its ability to generate strong humoral and cell-mediated immune responses and to provide good protection against both subcutaneous and intranasal Y. pestis challenge.

To identify the epidemiology and etiology characteristics of Tibetan sheep plague in Qinghai plateau.The background materials of Qinghai Tibetan sheep plague found during 1975 to 2009 were summarized, the regional, time and interpersonal distribution, infection routes, ecological factors for the spread were used to analyze; followed by choosing 14 Yersinia pestis strains isolated from such sheep for biochemical test, toxicity test, virulence factors identification, plasmid analysis, and DFR genotype.From 1975 to 2009, 14 Yersinia pestis strains were isolated from Tibetan sheep in Qinghai province. Tibetan sheep, as the infection source, had caused 10 cases of human plague, 25 plague patients, and 13 cases of death. All of the initial cases were infected due to eating Tibetan sheep died of plague; followed by cases due to contact of plague patients, while all the initial cases were bubonic plague. Cases of bubonic plague developed into secondary pneumonic plague and septicemia plague were most popular and with high mortality. Most of the Tibetan sheep plague and human plague occurred in Gannan ecological zone in southern Gansu province, which was closely related to its unique ecological and geographical landscape. Tibetan sheep plague coincided with human plague caused by Tibetan sheep, especially noteworthy was that November (a time for marmots to start their dormancy) witnesses the number of Yersinia pestis strains isolated from Tibetan sheep and human plague cases caused by Tibetan sheep. This constituted the underlying cause that the epidemic time of Tibetan sheep plague lags obviously behind that of the Marmot plague. It was confirmed in the study that all the 14 strains were of Qinghai-Tibet Plateau ecotype, with virulence factors evaluation and toxicity test demonstrating strains as velogenic. As found in the (Different Region) DFR genotyping, the strains isolated from Yushu county and Zhiduo county were genomovar 5, the two strain isolated from Nangqian county were genomovar 5 and genomovar 7, while those isolated Delingha region were genomovar 8.Tibetan sheep were vulnerable to plague infection, hence causing human plague as the infectious source. The Yersinia pestis strains isolated from Tibetan sheep plague carried pathogen characteristics of Qinghai-Tibet plateau plague, developing many new characteristics of such plague.

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.

Our previous study has demonstrated that Yersinia pestis Microtus 201 is a low virulent strain to the Chinese-origin rhesus macaques, Macaca mulatta, and can protect it against high dose of virulent Y. pestis challenge by subcutaneous route. To investigate whether the Y. pestis Microtus 201 can be used as a live attenuated vaccine candidate, in this study its intravenous virulence was determined and compared with the live attenuated vaccine strain EV in the Chinese-origin rhesus macaque model. The results showed that the Chinese-origin rhesus macaques can survive intravenous infection with approximately 10(9) CFU of the Y. pestis Microtus 201, but all the animals succumbed to 10(10) CFU of intravenous infection. By contrast, all the animals survive intravenous infection with 10(10) CFU of the vaccine EV. Post-mortem examination showed multiple areas of severe abscess in the lungs of the dead animals infected with 10(10) CFU of the Y. pestis Microtus 201, whereas histopathology observation, microbiological examination and immunohistochemistry staining showed that the Y. pestis Microtus 201 also invaded hearts, livers, spleens, kidneys and lymph nodes and caused different degrees of pathological changes in these organs. These results indicated that the Y. pestis Microtus 201 is indeed low virulent to monkeys, but it is more virulent than the vaccine EV when administered by intravenous route. The Y. pestis Microtus 201 mainly attack the lungs when administered by intravenous infection, which may be the leading cause of animal death.

To type Yersinia (Y.) pestis isolates under different regions (DFR) and to observe their geographical distributions in China.23 DFRs primers and PMT1 (plasmid) primer were used to verify the DFR genomovars of Y. pestiss strains from 11 plague foci in China. A total of 3 044 Y. pestis isolates were involved for analysis on DFR profiles with the characteristics of geographical distribution.52 genomovars were verified in 3 044 Y. pestis strains in China in which 19 genomovars as major and 33 genomovars as minor genomovar. 21 new genomovars, namely genomovar 32 to genomovar 52 were described on the basis of 31 genomovars previously confirmed. Three new genomovars belonged to new major genomovars, namely Himalayan marmot natural plague foci of the Qinghai-Tibet plateau newly added genomovar 32 and genomovar 44 as major genomovars. Mongolian gerbil natural plague foci of Inner Mongolia plateau were newly added genomovar 50 as one of the major genomovars.Among 21 new genomovars, 3 were major genomovars, with Chinese Y. pestis DFR as the major genomovars which had obvious distribution characteristics.

Shiga toxin-producing Escherichia coli (STEC) causes diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome in humans. Most human infections are attributed to consumption of STEC-contaminated foodstuffs of animal origin. In this study, we evaluated the prevalence of STEC from retail raw meats collected from two geographical regions in China. The results revealed that 166 out of 853 samples were stx-positive; 63 STEC isolates were recovered from 58 stx-positive samples including pork (4.4%, 14/318), beef (11.0%, 21/191), mutton (20.6%, 26/126), chicken (0.5%, 1/205), and duck (7.7%, 1/13). Twenty-six O serogroups and 33 O:H serotypes were identified. All three stx1 subtypes and five stx2 subtypes (2a to 2e) were found in the 63 STEC isolates, among which stx2e-positive STEC isolates were the most predominant (39.7%), followed by stx1c only (20.6%), stx1c+stx2b (14.3%), and stx1a only (9.5%). STEC isolates carried virulence genes eae (6.3%), ehxA (36.5%), katP (4.8%), astA (11.1%), and subA (36.5%). Of the four adherence-associated genes tested, toxB was absent, whereas saa, paa, and efa1 were present in 28, three, and one STEC isolates respectively. The STEC isolates were divided into 50 PFGE patterns and 33 sequence types. STEC from different sources and geographical regions were separated by PFGE and MLST. Our results revealed that there is a high genetic diversity of STEC in retail raw meats, some of which have potential to cause human diseases.

Dear Editor, As the causative agent of plague, Yersinia pestis has killed millions of people in the three major historical pandemics and remains endemic in many natural foci around the world today. This Gram-negative bacterium is transmitted to humans and susceptible animals from the natural rodent reservoirs through the bites of infected fleas, contact with infected animals or persons, or aerosols. Because of its respiratory transmission and high pathogenicity, the potential use of Y. pestis as a bioterrorism agent is a major concern. The specific and rapid detection of Y. pestis is the key step in implementing effective countermeasures during plague epidemics. The standard culture and biochemical identification methods for Y. pestis are relatively time-consuming, so PCR assays are frequently used because they are rapid. However, the amplification targets are usually based on three plasmids, which may be lost in atypical strains, causing false-negative results. Therefore, Radnedge et al. identified a signature sequence, designated “3a”, in a chromosomal region of Y. pestis, based on the results of suppression subtractive hybridization, which was later confirmed with a microarray-based analysis. A positive 3a result has been shown to be an effective marker for the identification of Y. pestis isolates. However, the recent isolation of 3a-negative Y. pestis in China suggests that this indicator is unreliable.

To study the biological and genetic characteristics of 119 strains of Yersinia (Y.) pestis isolated from plague patients in Qinghai province, from 1958-2012.Both regular methods and different region(DFR)molecular typing techniques were used to study the epidemiological characteristics on 119 strains of Y. pesticin Qinghai during 1958-2012. Sources of Y. pestis from two outbreaks, in Nangqian county in 2004 and in Xinghai county in 2009,Qinghai province were also analyzed.105 strains of Y. pestis were identified as Qinghai-Tibet Plateau Ecotype while the other 6 strains as Qilian Mountains Ecotype. 84.03% (100/119) of the tested strains carried 4 virulence factors F1(+), Pst I(+), VW(+) and Pgm(+)). 97.30% (72/74) of the tested strains showed high virulence. Strains that carrying 52×10(6), 65×10(6), 92×10(6) plasmids were distributed in Hainan, Haibei, Haixi,Yushu,Guoluo, Huangnan and Huangyuan counties. Genomovar 5 and 8 were the main gene types that circling around Qinghai Lake. Genomovar 10 was found in strains of Y. pesticin Nangqian county while Genomovar 8 was found in the strains isolated from human plague patient during the epidemics in Xinghai county in Qinghai.Data from biological and genetic analyses on the epidemics of human plague in Nangqian county in 2004 and in Xinghai county in 2009 demonstrated that methods as DFR genotyping and virulence factors profiles, as well as plasmids profiles were powerful tools in confirming the human plague epidemics and sources of infection.

Yersinia pestis biovar Microtus is considered to be a virulent to larger mammals, including guinea pigs, rabbits and humans. It may be used as live attenuated plague vaccine candidates in terms of its low virulence. However, the Microtus strain’s protection against plague has yet to be demonstrated in larger mammals. In this study, we evaluated the protective efficacy of the Microtus strain 201 as a live attenuated plague vaccine candidate. Our results show that this strain is highly attenuated by subcutaneous route, elicits an F1-specific antibody titer similar to the EV and provides a protective efficacy similar to the EV against bubonic plague in Chinese-origin rhesus macaques. The Microtus strain 201 could induce elevated secretion of both Th1-associated cytokines (IFN-γ, IL-2 and TNF-α) and Th2-associated cytokines (IL-4, IL-5, and IL-6), as well as chemokines MCP-1 and IL-8. However, the protected animals developed skin ulcer at challenge site with different severity in most of the immunized and some of the EV-immunized monkeys. Generally, the Microtus strain 201 represented a good plague vaccine candidate based on its ability to generate strong humoral and cell-mediated immune responses as well as its good protection against high dose of subcutaneous virulent Y. pestis challenge.

Shiga toxin (Stx)-producing Escherichia coli (STEC) are recognized as important human pathogens of public health concern. Many animals are the sources of STEC. In this study we determined the occurrence and characteristics of the STEC in yaks (Bos grunniens) from the Qinghai-Tibetan plateau, China. A total of 728 yak fecal samples was collected from June to August, 2012 and was screened for the presence of the stx 1 and stx 2 genes by TaqMan real-time PCR after the sample was enriched in modified Tryptone Soya Broth. Of the 138 (18.96%) stx 1 and/or stx 2-positive samples, 85 (61.59%) were confirmed to have at least 1 STEC isolate present by culture isolation, from which 128 STEC isolates were recovered. All STEC isolates were serotyped, genotyped by pulsed-field gel electrophoresis (PFGE) and characterized for the presence of 16 known virulence factors. Fifteen different O serogroups and 36 different O:H serotypes were identified in the 128 STEC isolates with 21 and 4 untypable for the O and H antigens respectively. One stx 1 subtype (stx 1a) and 5 stx 2 subtypes (stx 2a, stx 2b, stx 2c, stx 2d and stx 2g) were present in these STEC isolates. Apart from lpfA O157/OI-141, lpfA O157/OI-154, lpfA O113, katP and toxB which were all absent, other virulence factors screened (eaeA, iha, efa1, saa, paa, cnf1, cnf2, astA, subA, exhA and espP) were variably present in the 128 STEC isolates. PFGE were successful for all except 5 isolates and separated them into 67 different PFGE patterns. For the 18 serotypes with 2 or more isolates, isolates of the same serotypes had the same or closely related PFGE patterns, demonstrating clonality of these serotypes. This study was the first report on occurrence and characteristics of STEC isolated from yaks (Bos grunniens) from the Qinghai-Tibetan plateau, China, and extended the genetic diversity and reservoir host range of STEC.

Artificially passive immunization has been demonstrated to be effective againstYersinia pestisinfection in animals. However, maternal antibodies' protective efficacy against plague has not yet been demonstrated. Here, we evaluated the kinetics, protective efficacy, and transmission modes of maternal antibodies, using mice immunized with plague subunit vaccine SV1 (20 μg of F1 and 10 μg of rV270). The results showed that the rV270- and F1-specific antibodies could be detected in the sera of newborn mice (NM) until 10 and 14 weeks of age, respectively. There was no antibody titer difference between the parturient mice immunized with SV1 (PM-S) and the caesarean-section newborns (CSN) from the PM-S or between the lactating mice immunized by SV1 (LM-S) and the cross-fostered mice (CFM) during 3 weeks of lactation. The NM had a 72% protection against 4,800 CFUY. pestisstrain 141 challenge at 6 weeks of age, whereas at 14 weeks of age, NM all succumbed to 5,700 CFU ofY. pestischallenge. After 7 weeks of age, CFM had an 84% protection against 5,000 CFU ofY. pestischallenge. These results indicated that maternal antibodies induced by the plague subunit vaccine in mother mice can be transferred to NM by both placenta and lactation. Passive antibodies from the immunized mothers could persist for 3 months and provide early protection for NM. The degree of early protection is dependent on levels of the passively acquired antibody. The results indicate that passive immunization should be an effective countermeasure against plague during its epidemics.

In our previous study, complete protection was observed in Chinese-origin rhesus macaques immunized with SV1 (20 µg F1 and 10 µg rV270) and SV2 (200 µg F1 and 100 µg rV270) subunit vaccines and with EV76 live attenuated vaccine against subcutaneous challenge with 6×10(6) CFU of Y. pestis. In the present study, we investigated whether the vaccines can effectively protect immunized animals from any pathologic changes using histological and immunohistochemical techniques. In addition, the glomerular basement membranes (GBMs) of the immunized animals and control animals were checked by electron microscopy. The results show no signs of histopathological lesions in the lungs, livers, kidneys, lymph nodes, spleens and hearts of the immunized animals at Day 14 after the challenge, whereas pathological alterations were seen in the corresponding tissues of the control animals. Giemsa staining, ultrastructural examination, and immunohistochemical staining revealed bacteria in some of the organs of the control animals, whereas no bacterium was observed among the immunized animals. Ultrastructural observation revealed that no glomerular immune deposits on the GBM. These observations suggest that the vaccines can effectively protect animals from any pathologic changes and eliminate Y. pestis from the immunized animals. The control animals died from multi-organ lesions specifically caused by the Y. pestis infection. We also found that subcutaneous infection of animals with Y. pestis results in bubonic plague, followed by pneumonic and septicemic plagues. The histopathologic features of plague in rhesus macaques closely resemble those of rodent and human plagues. Thus, Chinese-origin rhesus macaques serve as useful models in studying Y. pestis pathogenesis, host response and the efficacy of new medical countermeasures against plague.